Discussion Questions:

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Courtesy of Mark Tuschman.

Skolnik, Richard. Global Health 101, Jones & Bartlett Learning, LLC, 2019. ProQuest Ebook Central, http://ebookcentral.proquest.com/lib/indianatech-ebooks/detail.action?docID=5894023. Created from indianatech-ebooks on 2022-09-15 00:20:57.

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CHAPTER 3 The Global Burden of Disease

LEARNING OBJECTIVES

By the end of this chapter, the reader will be able to do the following:

■ Discuss the concepts of health-adjusted life expectancy (HALE), disability-adjusted life years (DALYs), and the burden of disease

■ Describe the leading causes of disability, deaths, and DALYs by region, country income group, age, and sex

■ Describe the leading risk factors for disability, deaths, and DALYs by region, country income group, age, and sex

■ Discuss the demographic and epidemiologic transitions

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P ▶ Vignettes

rincess is a 3-year-old girl who lives near the town of Kenema in Sierra Leone. Although Sierra Leone has made

some progress in reducing young child death, the country remains very poor, still suffers from the ravages of its earlier civil war, and continues to have a very weak health system. Access to safe water and sanitation and good knowledge of hygiene are also limited. The burden of malaria has gone down, but the disease is still very prevalent. What are the leading causes of death for young children like Princess? What are the most important risk factors for those causes? Is there good evidence about what can be done in cost-effective and fair ways to reduce the burden of deaths among young children in Sierra Leone and similar countries?

Aisha is a 50-year-old woman who lives in the northern part of Nigeria. She is from a lower middle-class family, in an area that is still quite poor. Aisha has been feeling unwell and recently visited the outpatient clinic at the regional hospital. The check-up and tests the doctors carried out indicated that she has high blood pressure, high cholesterol, and diabetes. The doctors prescribed medicines for her to reduce her blood pressure and cholesterol and another drug to lower her blood sugar. As Aisha returned home, she thought about how people’s health had changed in the last decade in her town. Earlier, she rarely heard about the conditions with which she had been diagnosed. Now, however, it seemed like many of her friends had been diagnosed with the same problems.

Jose is a 30-year-old man in Bolivia. He is from an indigenous, relatively poor community in the highlands. Two decades ago, Jose’s community still faced many child deaths, especially from

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pneumonia and diarrhea. The community also had a substantial burden of undernutrition and tuberculosis (TB). To what extent have such causes of death declined in Jose’s community? If so, what are the leading causes of death now? Is there a “convergence” between the leading causes of death in Jose’s community and the lowland communities populated mostly by people of European descent?

Shireen is a 22-year-old woman in Bangladesh. She is just starting a family. Her mother and grandmother have given her advice about when to have her first child and where to get and how to use family planning methods. They have also suggested that she should have only two children and that she should space them 3 or more years apart. A community health worker has been in touch with Shireen regularly and has made the same suggestions as her mother and grandmother. In Bangladesh in 1960, women had on average more than six children and the median age of the population was around 19 years of age. In 2016, women had on average just over two children and the median age of the population was around 26 years of age. What causes these shifts? Do they occur consistently as countries develop socially and economically? What will the age distribution of the population look like in Bangladesh in 25 years and why?

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▶ Measuring the Burden of Disease The World Health Organization (WHO) defines health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity.” Those who work on global health have attempted for a number of years to construct a single indicator that could be used to compare how far different countries are from the state of good health. Ideally, such an index would take account of morbidity, mortality, and disability; allow one to calculate the index by age, by gender, and by region; and allow one to make comparisons of health status across regions within a country and across countries. This kind of index would measure what is generally referred to as the burden of disease.

One such indicator is health-adjusted life expectancy, or HALE. This is a health expectancy measure. HALE is the number of years a person of a given age can expect to live in good health, taking account of mortality and disability. This can also be seen as “the equivalent number of years in full health that a newborn can expect to live, based on current rates of ill health and mortality.” To calculate HALE, “the years of ill health are weighted according to severity and subtracted from the overall life expectancy.”

TABLE 3-1 shows life expectancy at birth in 2016 for a number of low-, middle-, and high-income countries and how it compares with HALEs for those countries in the same year, for males and females. In principle, each country should strive to help its people live as long and as healthy as possible. In that case, health- adjusted life expectancy and life expectancy at birth would converge at a relatively high number.

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TABLE 3-1 Life Expectancy at Birth and Health-Adjusted Life Expectancy by Sex, Selected Countries, 2016

The composite indicator of health status that is most commonly used in global health work is called the disability-adjusted life year, or DALY. This indicator was first used in conjunction with the 1993 World Development Report of the World Bank and is a health gap measure. It is now used consistently in burden of disease studies. In the simplest terms, a DALY is “the sum of years lost due to premature death (YLLs) and years lived with disability (YLDs). DALYs are also defined as years of healthy life lost.”

The calculation of years lost to premature death is based on the difference between the age at which one dies and one’s life expectancy at that age. To make this calculation, those involved in the key studies on the global burden of disease have constructed

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a reference standard life table that takes account of the highest life expectancy at birth globally. For the 2016 study, this was set at 86.6 years. This life table is used to calculate premature death for

all countries in the study.

One might ask why the study is not based on life tables for each individual country. In very simple terms, one could respond by noting that, in principle, any death before the life expectancy of the people who live the longest globally is “premature.” One might also add that in order to make the world a healthier place, a goal must be to have people live “as long as possible,” rather than live only as long as they live now.

FIGURE 3-1 illustrates the calculation of years of life lost due to premature death for three different scenarios.

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FIGURE 3-1 Calculating Years of Life Lost (YLLs) Due to Premature Death

Adapted with permission from Session 6, Module 2 of Essentials of Global Health,

Coursera/Yale University, 2016. Data from Institute of Health Metrics and Evaluation

(IHME). (n.d.). Global Burden of Disease Study 2016 (GBD 2016) data resources:

GBD 2016 reference life table. Retrieved from http://ghdx.healthdata.org/gbd-2016

As noted in Figure 3-1, if a newborn were to die in Liberia, for example, that newborn would have suffered 87 years of life lost due to premature death. Life expectancy at 40 according to the reference life tables is 87, or 47 more years. Thus, if a 40-year-old woman in Malawi were to die in a car accident, she would have

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http://ghdx.healthdata.org/gbd-2016

suffered 47 years of life lost due to premature death. Life expectancy at 60 years of age according to the standard reference life table is 88, or 28 more years. Thus, if a French male were to die of a heart attack at age 60, he would have suffered 28 years of life lost.

The value for years lived with disability is calculated by weighting these years by a disability index. For the Global Burden of Disease Study 2010, 14,000 people were surveyed directly and 16,000 people were involved via the internet in establishing disability weights. The disability weights used in the 2016 study were based on the 2010 weights, supplemented by data gathered from additional surveys done for the 2013 GBD study. The study authors also made some additional refinements to these weights, especially as they related to the severity of different health conditions.

FIGURE 3-2 illustrates the disability weights for five different conditions. It also shows model calculations of years of life lived with disability (YLDs) for three scenarios of people living with disability.

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FIGURE 3-2 Calculating Years Lived with Disability (YLDs)

Adapted with permission from Session 6, Module 2 of Essentials of Global Health,

Coursera/Yale University, 2016. Data from Salomon, J. A, Haagsma, J. A., Davis, A.,

de Noordhout, C. M., Polinder, S., Havelaar, A. H., . . . Vos, T. (2015). Disability

weights for the Global Burden of Disease 2013 study. Lancet Global Health, 3(11),

e712–e723.

As noted in Figure 3-2, let’s say that a person in Tanzania lives 30 years with a disability that has been given a weight of 0.10. In this case the person suffers 3 years of life lived with disability, equal to the number of years lived with disability, multiplied by the weight of

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that disability. If a person in France lived 20 years with a disability that has a weight of 0.25, then that person would have suffered the equivalent of 5 years lived with disability. If a person in Sri Lanka lived 10 years with a disability that has a weight of 0.5, then that person would have suffered 5 years of life lived with disability.

As noted earlier, a DALY is the sum of years of life lost due to premature death (YLL) and years of life lost due to disability (YLD). FIGURE 3-3 illustrates the calculation of a DALY for two different scenarios.

FIGURE 3-3 Calculating Disability-Adjusted Life Years (DALYs)

Adapted with permission from Session 6, Module 2 of Essentials of Global Health,

Coursera/Yale University, 2016.

As you can see in Figure 3-3, Person A dies at 50 years of age of drug-resistant tuberculosis, after living 3 years with this condition. In this case, the person’s life expectancy at 50 was 87. Thus the

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person suffered a loss of 37 years of life due to premature death. The disability weight for multidrug-resistant TB is 0.333. Thus, the person would have suffered 1 year of life lived with disability. The total DALYs for this person would be 37 plus 1, or 38.

Person B dies at 65 after living 10 years with moderate disability brought on by a stroke. This person died 23 years prematurely. This person also suffered about 3 years of life lived with disability. The total DALYs associated with this person would be 23 YLLs, plus 3 YLDs, or about 26 years.

A society that has more premature death, illness, and disability has more DALYs per person in the population than a society that is healthier and has less premature death, illness, and disability. One of the goals of health policy is to avert these DALYs in the most cost-efficient and fair manner possible. If, for example, a society has many hundreds of thousands of DALYs due to malaria that are not diagnosed and treated in a timely and proper manner, what steps can be taken to avert those DALYs at the lowest cost and in the fairest ways?

An important point to remember when considering DALYs, compared to measuring deaths, is that DALYs take account of periods in which people are living with disability. By doing this, DALYs and other composite indicators try to give a better estimate of the true health of a population instead of measuring deaths alone. This is easy to understand. Contrary to most popular belief, mental health problems, for example, are associated with an important number of deaths. However, they may also cause an enormous amount of disability. Several parasitic infections, such as schistosomiasis, cause very few deaths but large amounts of illness and disability. If we measured the health of a population with an important burden of schistosomiasis and mental illness only by measuring deaths, we would miss a major component of morbidity and disability and would seriously overestimate the

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health of that population. The next section elaborates on the concept of DALYs and how DALYs compare to deaths for a number of health conditions.

A number of critiques of DALYs have been written. Nonetheless, this text repeatedly refers to DALYs because this measure is so extensively used in global health work. In addition, a considerable amount of important analysis has been carried out that is based on the use of DALYs for measuring overall health status and assessing the most cost-effective approaches to dealing with various health problems.

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▶ Burden of Disease Data As you start a review of global health, it is important to get a clear picture of the leading causes of illness, disability, and death in the world. It is also very important to understand how they vary by age, sex, ethnicity, and socioeconomic status, both within and across countries. Additionally, it is essential to understand how these causes have varied over time and how they might change in the future. These topics are examined next.

Much of the data that follows on the burden of disease and risk factors is based on the findings of the Global Burden of Disease Study 2016, published in The Lancet in September 2017. The Institute of Health Metrics and Evaluation (IHME) coordinated that study. Those interested in the study methods may wish to consult the study directly. This chapter also heavily uses data from interactive data visualizations that the IHME has posted on its website. The reader should note that, while some data refer to “deaths” and some data refer to “DALYs,” references to the “burden of disease” refer to DALYs.

Wherever possible, data are shown by World Bank region or World Bank country income group. However, readers should be aware that the IHME data can be categorized into a range of regional groupings and by groups that are listed according to their ranking on a composite “social and economic development index” developed by the IHME.

Earlier burden of disease studies placed causes of deaths and DALYs into three categories:

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Group I—Communicable, maternal, and perinatal conditions (meaning in the first week after birth) and nutritional disorders

Group II—Noncommunicable diseases

Group III—Injuries, including, among other things, road traffic accidents, falls, self-inflicted injuries, and violence

The Global Burden of Disease Study 2016 does not use the groupings as they had been used earlier. Nonetheless, such groupings can be valuable to those who are new to the study of the burden of disease. Thus, they are used occasionally here.

Overview of Patterns and Trends in the Burden of Disease Understanding the patterns and trends in the burden of disease is central to understanding and dealing with key issues in global health. Some of the main findings of the burden of disease studies are summarized here :

■ People in much of the world are living longer than before. ■ Globally, women live longer than men by about 5 years on

average. ■ In the last 4 decades, there have been significant declines in

communicable, maternal, neonatal, and nutritional causes of death.

■ Globally, mortality rates have decreased for all age groups, with very substantial decreases for children under 5 years of age.

■ Nonetheless, there are substantial differences in the rate of mortality decrease across countries.

■ The years of life lost due to premature death are increasing for diabetes, some cancers, and, in some places, for drug use

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disorders, conflict, and terrorism. ■ The burden of disease is predominantly noncommunicable in

all World Bank regions and for all World Bank country income groups, except sub-Saharan Africa and low-income countries.

■ Over the last few decades, the burden of disease has shifted increasingly toward noncommunicable diseases in all World Bank regions and for all country income groups.

■ This shift has been fueled by, among other things, a reduction in communicable diseases and the aging of populations.

■ The 10 leading causes of total YLLs in 2016 were ischemic heart disease, cerebrovascular disease, lower respiratory infections, diarrheal diseases, road injuries, malaria, neonatal preterm birth complications, HIV/AIDS, chronic obstructive pulmonary disease, and neonatal encephalopathy due to birth asphyxia and trauma.

■ As life expectancies increase, death rates decline, and populations age, there is an increase in the number of years people live with disability, and this has increased as a share of the total burden of disease.

■ Globally, low back pain, migraine, age-related and other hearing loss, iron-deficiency anemia, and major depressive disorder were the five leading causes of years lived with disability in 2016.

■ Globally, the top 10 risk factors for the burden of disease are high blood pressure, smoking, low birthweight and short gestation, high fasting plasma glucose, high body mass index, ambient particulate matter, alcohol use, high total cholesterol, child growth failure, and household air pollution.

■ There are a number of countries in which life expectancy is greater than one might predict on the basis of social and economic development. These countries could provide some useful lessons for other countries that have not made such progress in health.

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The Leading Causes of Deaths and DALYs TABLE 3-2 shows the 10 leading causes of death and the 10 leading causes of DALYs by country income group for 2016. Both deaths and DALYs are ranked in order of importance.

TABLE 3-2 Leading Causes of Deaths and DALYs, by World

Bank Country Income Group, 2016

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TABLE 3-3 shows the 10 leading causes of deaths and DALYs by region.

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TABLE 3-3 Leading Causes of Deaths and DALYs, by World

Bank Region, 2016

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These tables and figures raise a number of key points concerning deaths and DALYs for all age groups and males and females globally:

■ The low-income countries have a unique pattern of deaths and DALYs, compared to other country income groups, that is still dominated by Group I causes. While about 61 percent of the total DALYs were associated with Group I causes in low- income countries, about 86 percent of total DALYs were associated with noncommunicable diseases (NCDs) in high- income countries.

■ The pattern of deaths and DALYs in lower middle-income countries has some resemblance to that in the low-income countries but also has similarities with the upper middle-income and high-income countries. In lower middle-income countries about 36 percent of total DALYs were associated with Group I

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causes, compared to 61 percent in low-income countries and 11 percent in upper middle-income countries.

■ There is a great deal of convergence in the causes of deaths and DALYs in the upper middle-income and high-income countries, both dominated by noncommunicable causes. About 77 percent of total DALYs were associated with noncommunicable diseases in upper middle-income countries, compared with 86 percent in high-income countries.

■ Injuries are important causes of deaths and DALYs. They make up between 8 percent and 11 percent of total DALYs, depending on the region.

■ The only Group I cause in the top 10 causes of death in upper middle-income and high-income countries is lower respiratory infections. While these are associated mostly with young child deaths in lower-income countries, they are associated mostly with deaths in older people in higher-income countries.

■ It is important to note the significance in most of the country income groups of DALYs attributable to low back and neck pain, sense organ diseases, skin diseases, and depressive disorders.

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PHOTO 3-1 A healthcare worker is pictured here, taking the blood pressure of a man in a health center in Mexico. Why is this so important? What risks does high blood pressure pose? What are some of the most important risk factors for having

hypertension?

Courtesy of Mark Tuschman.

In general, the higher the level of income of the countries in a region, the more likely it is that the leading causes of deaths and DALYs will be noncommunicable. The lower the level of income, the more likely it is that communicable diseases will be important. What is most essential to note is the extent to which the burden of disease in the sub-Saharan Africa region remains dominated by Group I causes and the continuing importance of these causes in the South Asia region, as well. Of course, these are in the face of a growing burden, even in these regions, of noncommunicable diseases.

Trends in the Causes of Deaths and DALYs, 1990–2016

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TABLE 3-4 indicates changes that have occurred between 1990 and 2016 in the leading causes of deaths and DALYs globally.

TABLE 3-4 Changes in the Leading Causes of Deaths and DALYs Globally, 1990 and 2016

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The table indicates the important extent to which the burden of deaths globally, when considering all age groups and both sexes, has shifted toward noncommunicable diseases. The trend has been similar for DALYs, with some significant shifts from communicable diseases and other Group I causes to noncommunicable diseases and injuries. In light of longer lives and aging populations, low back and neck pain and sensory organ disorders also appear in the list of 10 leading causes of DALYs in 2016, which was not the case in 1990. HIV/AIDS appears in 2016 and not in 1990 because the burden of HIV/AIDS was still relatively small in 1990.

Causes of Death by Age TABLE 3-5 shows the leading causes of death for children aged 0 to 5 years by country income group.

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TABLE 3-5 Leading Causes of Death in Children Under 5 by World Bank Country Income Group, 2016

The leading causes of deaths of under-5 children in low-income countries are dominated by communicable diseases—malaria, diarrhea, and lower respiratory infections. Conditions of the newborn and protein-energy malnutrition are also among the 10 leading causes of death of this age group in low-income countries.

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The leading causes of death among children under 5 years of age in lower middle-income countries does not differ significantly from the causes in low-income countries. As we move to upper middle- income countries, we see causes outside of Group I, including road injuries and drowning. The leading causes of death in high- income countries include congenital defects and neonatal conditions, as in the other country income groups. They also include lower respiratory conditions, which is an important cause of death for young children in all country income groups. However, in the high-income countries, 4 of the 10 leading causes of death in this age group are different from the leading causes in the other country income groups: sudden infant death syndrome, road injuries, endocrine and blood disorders, and mechanical forces.

TABLE 3-6 shows the leading causes of death for children ages 5 to 14 by country income group.

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TABLE 3-6 Leading Causes of Death in Children Ages 5–14 by World Bank Country Income Group, 2016

It is striking how the leading causes of death of children ages 5 to 14 in low- and lower middle-income countries are dominated by preventable or treatable communicable diseases, such as malaria, HIV/AIDS, lower respiratory diseases, and tuberculosis. Nutritional issues are also prominent in the lowest-income countries, and road traffic injuries and drowning are important causes of death in

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the low- and lower middle-income countries. In this age group, the significant shift in the causes of death occurs as one moves to upper middle-income countries and continues across the high- income countries. In these two country income groups, we see the importance of road injuries, drowning, violence, and cancers among the leading causes of death. In the high-income countries alone, self-harm is also among the 10 leading causes of death in this age group.

PHOTO 3-2 This picture depicts a group of older Ethiopian children. What health conditions are likely to be the most important causes of death for children 8 to 10 years old in

Ethiopia? How would that vary between better-off places and lower-resource places within Ethiopia?

Courtesy of Mark Tuschman.

TABLE 3-7 examines the leading causes of deaths and DALYs for the age group 15 to 49, by World Bank country income group.

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TABLE 3-7 Leading Causes of Deaths and DALYs, Ages 15–49, by World Bank Country Income Group, 2016

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A number of key points emerge from Table 3-7. The leading causes of death in low-income countries are strikingly different from those in the higher country income groups and still include a number of communicable diseases beyond lower respiratory infections, such as HIV/AIDS, tuberculosis, diarrheal disease, malaria, and meningitis. The leading causes of DALYs in this country income group, however, also include a number of conditions that are mostly linked with disability, including low back and neck pain, skin disease, depressive disorders, and migraines.

The leading cause of death in lower middle-income countries is ischemic heart disease. However, the leading causes also include a number of communicable diseases beyond the lower respiratory infections one would expect, such as HIV/AIDS, tuberculosis, and diarrheal diseases. The importance of road injuries, self-harm, and interpersonal violence is also striking for this group. The leading causes of DALYs in this country income group look quite similar to those for low-income countries but also include dietary iron deficiency.

The leading causes of deaths in upper middle-income countries suggest some important shifts compared to low- and lower middle- income countries. Like in the lower middle-income countries, the leading causes of death in this country income group include HIV/AIDS, interpersonal violence, and self-harm. However, in this country income group we also see the importance of cancers, as well as falls. The leading causes of DALYs in this country income group are similar to those for the lower middle-income country group.

The leading causes of death in the high-income countries suggest substantial shifts from the lower-income groups. Self-harm, road injuries, ischemic heart disease, and stroke are important in this

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group, as in lower middle-income and upper middle-income countries. However, we also see here the emergence of breast, lung, and colorectal cancers, as well as drug use and alcohol use disorders. The leading causes of DALYs in the high-income countries do include ischemic heart disease and road injuries, as one might expect. However, the prominence of several mental disorders, including depressive disorders and anxiety disorders, as well as drug use disorders and self-harm, is striking.

Causes of Deaths and DALYs by Sex It is also important to examine deaths and DALYs by sex, as shown in TABLE 3-8.

TABLE 3-8 Leading Causes of Deaths and DALYs by Sex, by World Bank Country Income Group, 2016

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When considering the leading causes of deaths and DALYs for females, it is important to remember that much of the global health literature on females focuses on reproductive health. While this is an important matter, it is essential to view female health more broadly. Every maternal death is unacceptable, but the leading cause of female death globally is ischemic heart disease, with stroke also being an important cause of death. We can also see that HIV/AIDS and TB remain important causes of female death in lower-income countries. As country income levels rise, diabetes, chronic obstructive pulmonary disease (COPD), a range of cancers, chronic kidney disease, and Alzheimer’s disease become increasingly important causes of death.

Because these data are for all age groups, we see a range of neonatal conditions as important causes of DALYs in the low- income country group, as well as nutritional issues. However, as country incomes rise, the leading causes of DALYs cluster increasingly around a number of noncommunicable causes, plus depressive disorders.

The leading causes of death among men of all ages do not differ greatly from the leading causes of death for women of all ages. However, COPD, road injuries, self-harm, and liver cancers are more important causes of death for men than for women, as, of course, is prostate cancer. The causes of DALYs for males of all ages follow a pattern similar to that for females.

In this case, too, diabetes, COPD, sense organ diseases, and skin diseases become increasingly important as country income levels rise. For males, however, road injuries and interpersonal violence are much more important causes of deaths and DALYs than for females.

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PHOTO 3-3 An indigenous woman in Guatemala is shown here being examined by healthcare workers in a local clinic.

What are the most important burdens of disease for women like the one shown? What are the most important risk factors for those burdens? Why is it so important to consider the health of women broadly and not just focus on their reproductive health?

Courtesy of Mark Tuschman.

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▶ The Burden of Deaths and Disease Within Countries

As you consider causes of death and the burden of disease globally and by country income group, region, age, and sex, it is also important to consider how deaths and DALYs vary within countries by gender, ethnicity, and socioeconomic status, among other things. Generally speaking, the following statements are true:

■ Rural populations will be less healthy than urban populations. ■ Disadvantaged ethnic minorities will be less healthy than

majority populations. ■ Females will suffer a number of conditions that relate to their

relatively disadvantaged social positions. ■ Lower-income people will be less healthy than better-off

people. ■ Uneducated people will be less healthy than better-educated

people.

In addition, people of lower socioeconomic status will have higher rates of communicable diseases, illness, and death related to maternal causes and malnutrition than will people of higher status. People of lower socioeconomic status will also suffer from a larger burden of disease related to smoking, alcohol, and poor diet than would be the case for better-off people. These points are fundamental to understanding global health.

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▶ Risk Factors As we discuss the determinants of health and how health status is measured, there will be many references to risk factors for various health conditions. A risk factor is “an aspect or personal behavior or life-style, an environmental exposure, or an inborn or inherited characteristic, that, on the basis of epidemiologic evidence, is known to be associated with health-related condition(s) considered important to prevent.” Risks that relate to health can also be thought of as “a probability of an adverse outcome, or a factor that raises this probability.” We are all familiar with the notion of risk factors from our own lives and from encounters with health services. When we answer questions about our health history, for example, we are essentially helping to identify the most important risk factors that we face ourselves. Do our parents suffer from any health conditions that might affect our own health? Are we eating in a way that is conducive to good health? Do we get enough exercise and enough sleep? Do we smoke or drink alcohol excessively? Are there any special stresses in our life? Do we wear seat belts when we drive?

If we extend the idea of risk factors to people with fewer resources, especially in low- and lower middle- income countries, then we might add some other questions that relate more to the ways that they live. Does the family have safe water to drink? Do their house and community have appropriate sanitation? Does the family cook indoors in a way that makes the house smoky? Do the parents work in places that are safe environmentally? We might also have to ask if there is war or conflict in the country, because they are also important risk factors for illness, death, and disability.

If we are to understand how the health status of people can be enhanced, then it is very important that we understand the risk

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factors to which their health problems relate. TABLE 3-9 shows the relative importance of different risk factors to deaths and DALYs for different country income groups. The burden of disease studies generally refer to these risks in three categories, behavioral, environmental and occupational, and metabolic, and it is valuable to keep this in mind as one considers risk factors.

TABLE 3-9 Leading Risk Factors for Deaths and DALYs by World

Bank Country Income Group, 2016

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There are two points that stand out as one looks at risk factors by country income group. First, consistent with the pattern of deaths and DALYs, the low- income countries continue to face a number of risks related to Group I causes, such as the lack of safe water and sanitation, household air pollution, low birthweight, and child growth failure. Beyond this, however, there is a noteworthy convergence of key risks for deaths and DALYs across the country income groups. These risks overwhelmingly relate to high blood pressure, smoking, ambient particulate matter, and dietary risks associated with overweight and obesity.

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PHOTO 3-4 The lack of access to safe water remains a major risk factor for ill health in many low- and lower middle-income countries. This picture shows a woman in India retrieving water for household use from an open source. What risks does this pose to the woman, her family, and her community? What is

likely to be the most cost-effective way of addressing those risks in the kind of community in which this woman lives?

Courtesy of Mark Tuschman.

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▶ Demography and Health

There are a number of points related to population that are extremely important to people’s health. These are among the most important:

■ Population growth ■ Population aging ■ Urbanization ■ The demographic divide ■ The demographic transition

These factors are briefly discussed next, along with their implications for health. Other important matters related to population, such as the relationship between fertility and the health of women and children, are discussed in other chapters.

Population Growth The population of the world was estimated in August 2018 to be about 7.6 billion and is still growing. As shown in FIGURE 3-4, it is estimated that by 2050 the population of the world will be about 9.9 billion.

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FIGURE 3-4 World Population 1950 to 2100

Modified from United Nations, Department of Economic and Social Affairs, Population

Division. (2017). World population prospects: The 2017 revision, key findings and

advance tables (Working Paper No. ESA/P/WP/248). New York, NY: United Nations.

Retrieved from

https://esa.un.org/unpd/wpp/Publications/Files/WPP2017_KeyFindings.pdf

As also shown in Figure 3-4, the overwhelming majority of population growth in the future will occur in low- and middle- income countries, especially in sub-Saharan Africa. This reflects the fact that fertility is falling slowly in many countries that have had high fertility rates historically, whereas many of the high- income countries already have very low fertility. In fact, some high- income countries are below replacement fertility. At a minimum, we should expect that increasing population growth in low-income countries will put substantial pressure on the environment, with its

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attendant risks for health. It will also mean that infrastructure, such as water supply and sanitation, will have to be provided to an increasing number of people in the countries that have the largest service gaps and can least afford to expand such services. This could cause these countries to face substantial impacts on health as a result. Increasing population will also make it more difficult for low-income countries to provide education and health services, with additional consequences for the health of their people in the future.

Population Aging As shown in TABLE 3-10, the population of the world is aging.

TABLE 3-10 Percentage of the Population Over 65 Years of Age, by WHO Regions and Globally, 2015, 2030, and 2050

This is especially true in high-income countries that have low fertility, but this is occurring in other countries as well. One impact

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of population aging is that it changes the ratio between the number of people that are 15 to 64 years of age, compared with the number that are 65 years of age or older. This is called the elderly support ratio. In Niger, with high fertility and a growing population, only 5 percent of the population in 2017 was over 65 years of age. By contrast, in Japan, with very low fertility and a shrinking population, 28 percent of the population was over 65 in 2017, as shown in Table 3-11.

Population aging and the shift in the elderly support ratio have profound implications for the burden of disease and for health expenditures and how they will be financed. In the simplest terms, people will live longer and experience more years with morbidities and disabilities, largely related to noncommunicable diseases. This will raise the costs of health care. In addition, the large numbers of older adults for every working person will make it difficult for countries to finance that health care.

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PHOTO 3-5 An older woman in India is shown in this photo. Which countries are aging the fastest? What impact is aging

likely to have on the burden of disease and why?

Courtesy of Mark Tuschman.

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Urbanization In the last 15 years, the majority of the world’s population has lived in urban areas for the first time in world history. People are continuing to move from rural to urban areas, especially in low- and middle-income countries in which important shares of the population have continued to live in rural areas until recently. Continuing urbanization will also put enormous pressure on urban infrastructure, such as water and sanitation, schools, and health services, which are already in short supply in many countries. Gaps in such infrastructure, as well as the development of crowded and low-standard housing, for example, could have substantial negative consequences for health.

The Demographic Divide Despite some convergence, there is an exceptional difference in the demographic indicators and future demographic paths of the best-off and the least-well-off countries, as suggested in the two previous sections. The highest-income countries generally have very low fertility, declining populations, and aging populations. By contrast, fertility in the lowest-income countries is generally still high, although it is declining slowly. In addition, the population is still growing in these countries and will continue to grow for some time. There is also an enormous difference in the health circumstances of the high- and low-income countries. TABLE 3-11 portrays the demographic divide.

TABLE 3-11 The Demographic Divide: The Example of Nigeria and Japan

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The Demographic Transition One important demographic trend of importance is called the demographic transition. Simply put, this is the shift from a pattern of high fertility and high mortality to low fertility and low mortality, with population growth occurring in between.

When we look back historically at the countries that are now high- income, we can see that they had long periods when fertility was high, mortality was high, and population growth was, therefore, relatively slow, or might even have declined in the face of epidemics. Beginning around the turn of the 19th century, however, mortality in those countries began to decline as hygiene and nutrition improved and the burden of infectious diseases lessened. In most cases, this decline in mortality started before much decline in fertility. As mortality declined, the population increased and the share of the population of younger ages also increased. Later, fertility began to decline and, as births and deaths became more equal, population growth slowed. As births and deaths stayed more equal, the share of the population that was of older ages increased. There are now some countries, as mentioned earlier, in which death rates exceed birth rates and the population is declining.

There are a number of ways to depict the demographic transition, one of which is shown in Figure 3-5.

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FIGURE 3-5 The Demographic Transition

Data from PopulationPyramid.net. (n.d.). Population pyramids of the world from 1950

to 2100. Retrieved from https://www.populationpyramid.net/world/2017/

The first “population pyramid” reflects a country with high fertility and high mortality, such as the low-income, high-fertility countries in sub-Saharan Africa. The second population pyramid is indicative of a country in which mortality has begun to decline but fertility remains high. This would be similar to the demographics one would find, for example, in a number of countries in sub- Saharan Africa that are undergoing demographic transition, or

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https://www.populationpyramid.net/world/2017/

Haiti, as noted. The third pyramid reflects a population in which fertility has been reduced for a substantial period of time, in which fertility is continuing to decline, and in which there is a much larger share of older people in the population than in the first and second pyramids. This would be similar to the demographics in a number of low-fertility, aging populations in the upper middle- and high- income countries. The fourth pyramid illustrates a country, such as Japan, Russia, or Australia, in which mortality rates are low and fertility rates are very low and the population shrinks in the absence of immigration.

The Epidemiologic Transition The epidemiologic transition is closely related to the demographic transition, as suggested throughout the previous discussion. Historically there has been a shift in the patterns of disease that follows these trends:

■ First, high and fluctuating mortality, related to very poor health conditions, epidemics, and famine

■ Then, progressive declines in mortality as epidemics become less frequent

■ Finally, further declines in mortality, increases in life expectancy, and the predominance of noncommunicable diseases

FIGURE 3-6 shows the distribution of deaths by groups of causes, by World Bank country income group. FIGURE 3-7 shows the distribution of DALYs.

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FIGURE 3-6 Distribution of Deaths by Cause Group, for World Bank Country Income Groups

Data from Institute of Health Metrics and Evaluation (IHME). (n.d.). GBD Compare:

Viz Hub. Retrieved from https://vizhub.healthdata.org/gbd-compare/

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FIGURE 3-7 Distribution of DALYs by Cause Group, for World Bank Country Income Groups

Data from Institute of Health Metrics and Evaluation (IHME). (n.d.). GBD Compare:

Viz Hub. Retrieved from https://vizhub.healthdata.org/gbd-compare/

You can see in Figures 3-6 and 3-7 how the pattern of deaths and DALYs differs between the low-, middle-, and high-income countries. You can also see the changes that will occur over time, as the burden of disease in lower-income countries moves from

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one with a substantial share of communicable diseases to one in which noncommunicable diseases are predominant.

The pace of the epidemiologic transition in different societies depends on a number of factors related to the determinants of health that were discussed earlier. In its early stages, the transition appears to depend primarily on improvements in hygiene, nutrition, education, and socioeconomic status. Some improvements also stem from advances in public health and in medicine, such as the development of new vaccines and antibiotics.

Most of the countries that are now high-income went through epidemiologic transitions that were relatively slow, with the exception of Japan. Most low- and middle-income countries have already begun their transition; however, it is still far from complete in many of them.

In fact, most low-income countries are in an ongoing epidemiologic transition, and many of them, therefore, face significant burdens of communicable and noncommunicable diseases and injuries at the same time. This strains the capacity of the health system of many of these countries. It is also expensive for countries that are resource-poor to address a substantial burden of all three of these types of conditions simultaneously.

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▶ Progress in Health Status There has been substantial progress in improving health and raising life expectancy in all parts of the world. However, those gains have not been uniform across regions or countries. Rather, life expectancy in sub-Saharan Africa and South Asia continues to substantially lag behind that in other regions. In addition, for countries that had a life expectancy in 1960 of less than 50 years, the pace of improvements in life expectancy in sub-Saharan Africa has been much slower than in any other region.

TABLE 3-12 shows life expectancy in 1960, 1990, and 2016 by World Bank region. The table also shows the percentage gain in life expectancy over three different periods, 1960 to 2016, 1960 to 1990, and 1990 to 2016.

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TABLE 3-12 Life Expectancy and Percentage Gain in Life Expectancy, by World Bank Region, 1960-2016

Life expectancy grew over each period in each region; however, the increases in Europe and Central Asia were small in the period from 1990 to 2016, largely reflecting the social and economic consequences of the breakup of the former Soviet Union and the impact of changes on the health system as well. The slowdown in progress in improving life expectancy in sub-Saharan Africa between 1990 and 2016, although still very substantial, mostly reflects the negative impact on life expectancy of the HIV/AIDS epidemic, as well as slow economic progress in some countries and political conflict. The slow increase in life expectancy in the last period in North America reflects not only the high base from which it started but also the impact on life expectancy of an epidemic of substance abuse in the United States. By contrast, the

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dramatic increases in life expectancy from 1960 to 2016 in much of the low- and middle-income world reflects the rapid pace of economic development in many low- and middle-income countries, usually accompanied by improvements in infrastructure, nutrition, education, and health.

The factors that lead to improvements in health are complex. Additional comments are made at the end of this chapter about these factors, including the role, for example, of nutrition, education, political stability, and scientific improvements. Many other chapters also include comments on the progress in improving the health of women and children and in addressing particular causes of illness, disability, and death.

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▶ The Burden of Disease: Looking Forward The burden of disease in the future will be influenced by a number of factors that will continue to change. Some of these will relate to the determinants of health. Some will relate to the demographic forces just discussed, including population growth, population aging, and migration. The burden of disease in the future will also be driven by, among other things, the following factors:

■ Economic development ■ Scientific and technological change ■ Climate change ■ Political stability ■ Emerging and re-emerging infectious diseases

These are discussed very briefly in the following sections.

Economic Development The economies of low-income countries will need to grow if those countries are to generate the income they need to invest in improving people’s health and well-being. The impact of economic development on health will depend partly on the extent to which economic growth is equitable across population groups. It will also depend on the extent to which countries are able—or choose—to use their increased income to invest in other areas that improve health, such as water, sanitation, hygiene, food security, and education. The extent and appropriateness of their investments in health, such as in low-cost, high-yielding efforts, will also be critical.

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Scientific and Technological Change Scientific and technological change has had an enormous impact on health and will continue to have an impact in the future. This is easy to understand, as one considers the development of vaccines or new drugs, such as antibiotics or antiretroviral therapy. The development of improved diagnostics for TB, for example, would have an substantial impact on the health of the world, as would the development of a vaccine against HIV or malaria. The impact of scientific and technological change on the low-income countries of today will depend to a large extent on the pace at which they are able to effectively adopt any improvements when they are developed.

Climate Change The full extent of the impact of climate change on health is not clear; however, it is anticipated that climate change and its attendant impact on weather and rising sea levels could directly and indirectly have an important impact on health. On the indirect side, climate change could alter the nature of the food crops that can be grown in different places and food security and lead to migration from some places to others that are deemed more habitable. On the more direct side, climate change could lead to weather changes and adverse weather that harm people’s health. It could also lead to the disappearance of disease vectors in some places as the weather is no longer hospitable to them, while allowing the emergence or re-emergence of disease vectors in other places.

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Political Stability In low-income countries, political stability appears to be necessary for achieving long-term gains in health. There is substantial evidence, for example, that the lack of political stability was a major impediment to progress in achieving the Millennium Development Goals in a number of countries. It is not hard to imagine, for example, how conflicts that occurred in Liberia, Sierra Leone, and the Democratic Republic of the Congo could set back health status for many years. These conflicts led directly to substantial illness, disability, and death. In addition, by causing a breakdown in infrastructure, such as water, sanitation, and electricity, as well as the erosion of health services, they also had enormous indirect impacts on health.

Emerging and Re-emerging Infectious Diseases It is not possible to predict if and when new diseases will emerge or diseases already known will re-emerge. It is also not possible to know how well individual countries and the world will do in recognizing such problems as they arise and addressing them quickly and effectively. What is clear is that pandemic flu, for example, could have a major impact on future disease patterns. It is also clear, for example, that if the growth of drug resistance for, say, malaria, outpaced our ability to produce safe and effective drugs to fight malaria, this, too, could have a substantial impact on the burden of disease.

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▶ The Development Challenge of Improving Health

One of the key development challenges facing policymakers in low-income countries is how they can speed the demographic and epidemiologic transitions at the lowest possible cost. How can Niger, for example, improve its health status as rapidly as possible, at the least possible cost, and in the fairest ways? Will it be possible for the people of Niger to enjoy the health status of a middle-income country, even if Niger remains a low-income country?

FIGURE 3-8 shows national income of a sample of countries, plotted against life expectancy at birth for females in those countries. From this figure, one can see that, generally, the health of a country does increase as national income rises. However, one can also see that there are some countries, such as Bangladesh, Jordan, Peru, China, and Malaysia, that have achieved higher average life expectancies at birth for females than one would have predicted for countries at their level of income. At the same time, one has to ask why a country like Pakistan, with a similar per capita national income to Bangladesh and Cambodia, has lower female life expectancy than those countries have.

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FIGURE 3-8 Gross Domestic Product per Capita and Female Life Expectancy at Birth, Selected Countries

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Data from The World Bank. (n.d.). Life expectancy at birth, female (years) and GDP

per capita (current US$). Retrieved from https://data.worldbank.org/

To a large extent, countries that have done better than one might expect in increasing life expectancy at birth for females (and males) achieved their health gains as a result of the following:

■ Investing effectively and efficiently in areas that address key risk factors and determinants of health, including water, sanitation and hygiene, nutrition, and education

■ Investing effectively and efficiently in relatively low-cost but high-impact health services, such as vaccination and the control of communicable diseases

■ Taking a community-based approach to primary health care

Indeed, in the long run, economic progress will help to bring down fertility, reduce mortality from communicable diseases, and help to produce a healthier population. However, at the present rates of progress in improving health in most low-income countries, these changes will take a very long time to occur. One considerable public policy challenge for these countries and their governments, therefore, is how they can short-circuit this process and reach reduced levels of fertility, lower mortality, and better health for their people, even as they remain relatively low-income.

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https://data.worldbank.org/

▶ Case Study One case study follows. It deals with an effort, called the Million Death Study, to gather valid data on deaths in India at a sustainable cost and in ways that are replicable.

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The Aims of the Million Death Study The Centre for Global Health Research, at the University of Toronto, Canada, is carrying out the Million Deaths Study in India in conjunction with the Registrar General of India. This study is one of the largest research efforts ever undertaken on the causes of premature mortality. Led by Professor Prabhat Jha, the study aims to help India improve the documentation of the underlying causes and risk factors of mortality as a basis for enhancing investments in health, reducing premature death, and improving the health of India’s people.

Vital statistics, such as fertility and mortality data, are crucial for identifying major health issues, identifying new health problems as they arise, making cost-effective public health investments, and evaluating the progress of public health interventions. Yet reliable mortality statistics are rare. As much as 75 percent of global deaths occur in low- and middle-income countries, and the majority of these lack medical supervision and official certification of cause of death. In India, for example, 70 percent of deaths go unreported or misclassified. Previous mortality estimates for India were largely based on data from the limited spectrum of deaths that occur in hospitals and were consequently biased toward causes of death that affect urban populations more than rural populations. They were also biased toward conditions that are more urgent and lead to hospitalization, rather than taking sufficient account of chronic health problems. Moreover, in India and in many other middle- and low-income countries, there is a general dearth of knowledge around the causes of death, especially for middle-aged adults, and the corresponding risk factors leading to premature death.

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The Study Approach The Million Death Study seeks to assess the causes of death of 1 million people in India through monitoring 2.4 million households over two time periods: 1998 to 2003 and 2004 to 2014. The study is based on an approach called “verbal autopsy.” The study uses India’s Sample Registration System as its sampling framework. Twice a year, trained surveyors conduct surveys in order to identify households in which a death occurred. They then interview household members about the deaths in their families and record information on the events leading to death and the symptoms of the deceased. The verbal autopsies are sent to two independent physicians to be analyzed and ascertain the underlying cause of those deaths. By early 2015, 600,000 deaths had been surveyed and 400,000 deaths had been fully coded.

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Key Findings to Date The study thus far has exposed some mortality estimates and trends that deviate from those previously recognized. First, the study has suggested that the top four causes of death in India are cardiovascular disease, chronic respiratory disease, TB, and cancer. Second, one of the most striking findings is related to the effects of tobacco. The average Indian smoker starts smoking later in life than in many other countries and often smokes hand-rolled locally manufactured cigarettes called bidis, which have a lower concentration of cancer-causing agents than commercially manufactured cigarettes. Nonetheless, this study showed that in India, smoking is as much a risk factor for premature death as in Europe and the United States. Moreover, study findings suggest that smoking is a risk factor for TB in India and that 40 percent of all TB deaths in middle-aged men in India can be attributed to smoking. Third, the study suggests that some estimates of the burden of disease might be quite different from what was previously thought and that the burden of disease pattern varies greatly across the country. This study, for example, estimates that total malaria deaths are 10 times greater than the World Health Organization estimates, with over half of malaria deaths occurring in people ages 15 to 69 and the state of Odisha accounting for a quarter of India’s annual malaria deaths. On the other hand, the

study suggests that mortality associated with HIV-related infections is lower than UNAIDS estimates, although the rural areas around Mumbai have a particularly high concentration of HIV-related deaths, with an annual death rate of 56 per 100,000. The study has also led to revised estimates of the

number of girls who are “missing” due to sex-selective abortion and suggested that most suicides are among young adults, rather than among adult farmers, as had previously been thought.

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Lessons of Experience The Million Death Study may offer a model for improving mortality information that is reliable, high impact, low cost, and replicable in other countries. The ideal system to measure mortality would depend on a well-functioning system of vital registration. However, in the absence of such comprehensive registration programs, this study suggests that verbal autopsies can reduce inaccurate data by correctly classifying the underlying causes of 90 percent of the deaths occurring before age 70, an order of magnitude better than the limited cause of death data previously available. This can help derive the probable cause of death when one has not been reported and help us to understand the leading causes of death. Importantly, this approach has also been shown to be cost- effective. India added recording the causes of death and risk factors to a low-cost, preexisting sample registration system, at a cost of less than $2 per household.

The long-term goal will always be universal civil registration of deaths with medical certification in order to minimize misclassification and misrepresentation. However, approaches such as those applied in the Million Death Study offer an interim solution for better statistics on mortality for many low- and middle- income countries.

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▶ Main Messages To understand and address the most important global health issues, we must understand the burden of disease, the risk factors for that burden, and how those vary among different population groups. Over the last several decades, the global burden of disease studies have provided the most comprehensive information on these matters.

These studies have also developed an important metric for assessing the burden of disease, the DALY. The DALY goes beyond measuring only deaths to provide an understanding of the amount of healthy life years lost due to both premature death and to years lived with disability. It is easy to understand the importance of the DALY when we consider causes of ill health that do not necessarily lead to death but that can lead to many years of disability, such as depressive disorders, musculoskeletal disorders, and the neglected tropical diseases.

The leading cause of death worldwide for both sexes and all age groups is ischemic heart disease, followed by stroke. All of the other 10 leading causes of death globally, except lower respiratory infections, HIV/AIDS, and TB, are noncommunicable diseases. The leading cause of DALYs for both sexes and all age groups globally is also ischemic heart disease when looking at both sexes combined and all age groups combined. However, the 10 leading causes of DALYs also include several diseases that especially affect large numbers of children in lower-income countries, such as diarrhea and malaria. The leading causes of DALYs also include road traffic injuries and low back pain.

The burden of disease is predominantly noncommunicable in all regions of the world except sub-Saharan Africa, and South Asia also continues to have a substantial burden of communicable

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disease. Over the last several decades, the burden of disease within regions and globally has continued to shift more and more toward a pattern dominated by noncommunicable diseases. Barring major outbreaks of communicable disease, this trend will continue, especially in the face of populations that are aging. This movement from a pattern of disease that is largely communicable to one that is largely noncommunicable is called the epidemiologic transition.

It is also important to understand the most important risk factors that are associated with deaths and DALYs. In the low-income countries, some of the most important risk factors include a range of nutritional issues, the lack of safe water or safe sanitation, indoor and ambient particulate matter pollution, and tobacco smoking. Poor diets that relate to obesity, high blood pressure, high cholesterol, and cardiovascular disease are becoming increasingly important problems as well, even in low-income countries. In the higher-income countries, the key risk factors for deaths and DALYs are overwhelmingly behavioral and have to do with what people eat, their levels of physical activity, and if they smoke tobacco, engage in excessive alcohol use, and drive safely. Ambient particulate matter pollution is also an important risk factor in the higher-income countries.

An understanding of basic demographic trends is also very helpful to understanding and addressing key global health issues. The three demographic trends that will have the most important impacts on health are the continuing increase in the global population, almost all from increases in low- and lower middle- income countries; the universal aging of populations; and the increasing urbanization of the world. Another fundamental concept that it is important to understand is the demographic transition. This refers to the movement over time from a pattern of high mortality and high fertility to one of low mortality and low fertility.

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Study Questions 1. If you could pick only one indicator to describe the health

status of a low-income country, which indicator would you use and why?

2. Why is it valuable to have composite indicators like the DALY to measure the burden of disease?

3. As countries develop economically, what are the most important changes that occur in their burden of disease?

4. Why do these changes occur? 5. How might the burden of disease differ from one region to

another in a large and diverse country such as India or Nigeria?

6. How do we expect the burden of disease to evolve globally over the next 20 to 30 years?

7. What is the epidemiologic transition? 8. What is the demographic transition? 9. What are the leading causes of death of young children in

low-income countries? 10. What are the leading causes of death in high-income

countries, and how are they similar to and different from the causes in low-income countries?

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