Discussion paper due in 24 hours from now !!!!

The objectives of the study are as follows:

1. To assess and compare selenium intake and blood levels in males and females with DM aged 40 years;

2. To determine whether there is a relationship between serum selenium concentrations and levels of fasting blood glucose and hemoglobin A1c, and whether the relationship is similar in males versus females with DM aged 40 years;

The following hypotheses will be tested:

1. There are gender differences in the concentration of serum selenium in persons with DM aged 40 years, with females having significantly lower serum selenium levels;

2. Selenium intake of both US men and women, either from food and/or supplements, will exceed the RDA by more than double. There will be significant differences between females and males regarding selenium intake with female consuming significantly less selenium than males;

3. Higher selenium levels will be associated with higher fasting plasma glucose. The relationship will be stronger in males compared to females;

4. There will be a positive relationship between HbA1c and serum selenium levels in males and females with DM aged 40 years old. The relationship will be stronger in males versus females.

5. Age will be related to serum selenium levels in people with DM. Oldest age clusters ( 80 years old) will have the highest serum selenium levels.

Literature review

Type 2 diabetes is the most common form of diabetes and is caused by a progressive increase in insulin resistance. Its relation to oxidative stress seems to reflect the excess of reactive oxygen species levels in hyperglycemia. As such, oxidative stress has a huge impact on the etiology, pathogenesis and complications of type 2 DM. Thus, this component may play a protective role against type 2 DM. However, the relationship of selenium to type 2 DM is rather complex. On one hand, an overexpression of selenium-dependent glutathione peroxidases in the islets can protect pancreatic β cells from oxidative stress, stimulate pancreatic β cell gene expression and improve islet function. On the other hand, high concentrations of selenium in the body can interfere with insulin signaling, a critical point in the regulation of glucose levels and in the prevention of diabetes.

High serum selenium concentrations, achieved from dietary intake, are associated with a higher occurrence of diabetes, higher fasting plasma glucose and increased glycosylated hemoglobin levels (Rocourt & Cheng, 2013). Wei et al. (2015) found a positive and significant association between dietary intake of selenium and diabetes, for the highest quartile of dietary selenium intake in comparison with the lowest quartile (OR=1.52, 95% CI: 1.01 to 2.28) (Wei et al., 2015). These results are supported by another study performed in rural China involving 1,856 subjects with 65 or more years old, which showed that, a long-term, higher level of exposure to selenium may be associated with a higher risk of diabetes. In other words, the authors found a significant increased risk of DM from the second selenium quartile to the fourth quartile (OR= 2.65, 95% CI: 1.48 to 4.73; OR= 2.47, 95% CI: 1.37 to 4.45); OR= 3.30, 95% CI: 1.85 to 5.88) by performing a logistic regression model used to estimate odds ratios for diabetes between the four Se quartile groups for all participants (SU et al., 2016).

However, some studies showed different results. A study conducted in Italy involving a cohort followed for 16 years with 226 women of type 2 DM and 395 age-matched control women, found that toenail and dietary selenium were uncorrelated and found no association between toenail selenium and subsequent development of diabetes (Vinceti et al., 2015). Furthermore, a randomized control trial with placebo versus selenium supplementation in patients diagnosed with DM, fasting plasma glucose, glycosylated hemoglobin Alc, and high-density lipoprotein cholesterol were shown to be statistically significantly higher in the selenium recipient arm (Faghihi et al., 2014). Also, in a randomized trial aiming to access the diabetogenic power of selenium involving 473 participants over a period of 6 months taking 100, 200 or 300 µg selenium/d as high-selenium or placebo yeast, selenium supplementation, independently of the dose, had no effect on plasma adiponectin concentration (Rayman et al., 2012).

Additionally, another study reporting the incidence of type 2 DM in U.S. men and women, found that individuals with higher toenail selenium levels are at lower risk for type 2 DM (Park et al., 2012). However, this study did not account for the potential confounder effect of food supplementation. This aspect may be important because high levels of Se consumption from supplements may have different effects than those of modest dietary doses. Also, a 20 years Swedish study involving 1925 Swedish men who were 50 years old, the incident cases of DM were not associated with higher selenium concentration, nor was a significant odds ratio for DM development found (H. Gao et al., 2014). Moreover, in a study aiming to assess the effects of selenium supplementation for 12 weeks on biomarkers of inflammation and oxidative stress in patients with diabetic nephropathy, was shown that taking selenium supplements had no significant effects on fasting plasma glucose (FPG), quantitative insulin sensitivity check index (QUICKI) and lipid profiles compared with the placebo (Bahmani, Kia, Soleimani, Asemi, & Esmaillzadeh, 2016).

There are also inconclusive studies, unable to adjudicate for or against selenium supplementation because of a lack of evidence or statistically significant results. A meta-analysis of randomized controlled trials showed that no association existed between selenium and DM. Therefore selenium supplementation was not recommended for these groups of patients (Mao, Zhang, & Huang, 2014).

The association between selenium and DM has been controversial, with some studies that concluding that selenium may be a protective factor, and other studies that show the contrary. However, many of the studies conducted were not primarily aimed at evaluating selenium and its effects on the development of DM, but they were part of more general studies, or even studies of cancer protection with selenium supplementation, which could induce abnormally high levels of selenium intake. It is important to note here the hypothesis that selenium concentrations have a U-shaped effect, in which the optimum dose should be maintained in order to enhance the beneficial and protective effects of selenium (M. P. Rayman & Stranges, 2013). These findings are supported by a recent review including a total of five studies and 13,460 participants. In this review, a non-linear association was found between selenium and T2DM, indicating that a U-shaped curve is a possible explanation for the relationship between selenium and DM (Wang et al., 2015).

In a view of its important function in protection against oxidative stress, selenium was suggested to play a protective role against Type 2 DM. Although some studies have tried to clarify this association, their findings are still inconclusive and contradictory. Some studies found that selenium could reduce the prevalence of DM (Rajpathak et al., 2005), others suggested that high levels of selenium are related to increased prevalence of this chronic disease (Bleys et al., 2007). A placebo-controlled trial of selenium supplementation in patients with DM has shown that selenium supplementation in patients with DM may be associated with adverse effects on blood glucose homeostasis (Faghihi et al., 2014).

Selenium is also capable of influencing carbohydrate and lipid metabolism and thus may impact the DM risk (Steinbrenner, 2013). Selenium concentration in humans are frequently achieved from serum, plasma, or toenails. In a cohort study with a mean follow-up of 16 years, without intervention, no associations between toenail selenium and subsequent development of DM were found (Vinceti et al., 2015). The finding of another study, a Swedish cohort study, suggested that even when analyzing participants who were 50 years or older, researchers failed to demonstrate any association between dietary selenium in the development of disturbances in glucose metabolism or DM (H. Gao et al., 2014). A meta-analysis of randomized controlled trials of selenium supplementation involving 20,294 participants also failed to find any support for the routine application of selenium supplementation for Type 2 DM prevention (Mao et al., 2014).

In contrast with the previous studies where no association was found, research describing the incidence of Type 2 DM in U.S., found that toenail selenium are lower among diabetic men with or without CVD than among healthy controls (Rajpathak et al., 2005). On the other hand, (Ogawa-Wong et al. 2016) reported that there is an increased risk of DM in individuals with high baseline selenium levels. Also, a meta-analysis of observational studies with a total of 13,460 participants described a U-shaped association between selenium serum levels and Type 2 DM, where both relatively low levels and high levels of serum selenium were positively associated with Type 2 DM (Wang et al., 2015). Lu et al. (2016) assessed the connection between high concentrations of selenium and increased risk of DM. In this health center –based controlled study, with a sample of 847 adults who were over 40 years old in Northern parts of Taiwan, it was demonstrated that selenium levels were positively connected with DM predominance. Also, it was found that the association existing between the selenium and DM did not depend on insulin resistance. Similarly, a cross-sectional study of 5,423 subjects of Chinese origin showed the association between selenium and DM (Gong, Q., Yang, Lei & Yang, 2015). In the study, the primary characteristics, the biochemical test outcomes and the dietary ingestion were analyzed from individual participants. Results showed a positive relationship between DM and selenium dietary ingestion.

2.3.2. Gender in Diabetes-Selenium Relationship

Due to the sexual dimorphism in the regulation of selenium, it is not a surprise that some studies have been trying to establish a relationship between selenium, DM and gender.

Selenium is co-translationally inserted into the growing peptide chain of selenoproteins in the form of 21st proteinogenic amino acid, selenocysteine. This difference in relation to other minerals is fundamental for all aspects associated with the metabolism of selenium and the differences found between the tissues of males and females in expression patterns (Schomburg & Schweizer, 2009a). However, none of the genes coding for selenoproteins or for factors that incorporate selenocysteine are present on sex chromosomes (A. Seale, N. Ogawa-Wong, & J. Berry, 2018). Thus, the differences found in the expression of selenoproteins and factors that incorporate selenocysteine are under the regulation of other factors such as sex hormones, directly influencing the production of testosterone. Additionally, the regulation of sex hormones implies that the metabolism of selenomethionine and the consequent formation of selenocysteine and availability for the synthesis of selenoproteins is different between sexes.

Regarding nutritional intakes, retention of selenium can be determined by the differences in the amount of selenium ingested along with the sum of what is lost through urine and feces. Thus, the greater the selenium intake, the greater the urine excretion. However, women do not retain selenomethionine as well as men (Stipanuk & Caudill, 2013). There is a higher dose-dependent urinary selenium excretion compared to men. However, the differences in selenium intake between males and females is not significant when the intake is calculated per kilogram of body weight (Wendel, 2012).

Studies using data from the third National Health and Nutrition Examination Survey (NHANES) found correlations among these parameters. For instance, NHANES III, found a correlation between T2DM risk and high selenium in males, but not females, a finding which was supported by NHANES 2003–2004 (Laclaustra, Navas-Acien, Stranges, Ordovas, & Guallar, 2009). Furthermore, a study conducted in 2017 found a high correlation of total selenium and selenoprotein P concentrations in young and elderly men, and in elderly women, but not in young women, indicating a specific sexual dimorphism in these biomarkers of selenium status in young subjects (Hybsier et al., 2017). As such, understanding gender differences in biological function of selenoproteins may help understand the contribution of individual selenoproteins in metabolic diseases. Human clinical trials hint at the possibility that the relationship between selenium and DM is sex-specific. In the Nutritional Prevention of Cancer (NPC) trial, the increased risk of DM in response to Selenium supplementation was limited to males (Stranges et al., 2007). On the other hand, but still supporting the hypothesis the selenium and DM interrelationship is sex-specific, another study reported a correlation between lower baseline Selenium (GPx1 polymorphisms) and T2DM incidence among elderly French men, but not women (Akbaraly et al., 2010).

Although sex differences in the association between selenoprotein S (SelS)and metabolic diseases have not yet been described, there are sex differences in the amount of selenium necessary to reach maximal hepatic SelS expression (Stoedter, Renko, Hog, & Schomburg, 2010). The different SelS expression may contribute to low effectiveness of Selenium supplementation. One cannot exclude the possibility that sex differences in the regulation of SelS, may result in sex-specific outcomes in metabolic diseases such as DM (Y. Gao et al., 2004). Wei et al. (2015), found a small positive association between selenium intake and DM in males, but this did not reach statistical significance. In females a significant positive association between selenium intake and DM was not found. It has been suggested that selenium metabolic pathogenesis influences carbohydrate and lipid metabolism, strengthening the idea that selenium does in fact play a role in Type 2 DM. However, the sexually dimorphic association between selenium and metabolic diseases reveals the complexity of the processes. To reduce potentially undesirable effects of selenium supplementation, and to further improve dietary guidelines, there is an urgent need to understand selenium metabolism and selenoproteins in both male and female subjects (Ogawa-Wong, 2016).

The relationship between selenium, Type 2 DM, and gender, has not been much studied yet. Studies that investigate this relationship are scarce. Selenium is an essential trace element for its antioxidant, anti-inflammatory, chemo preventive and antiviral activities. Selenium plays an important role in the metabolism of thyroid and glucose, immunity cellular and reproductive function (Margaret P Rayman et al., 2012). It is possible to believe that gender differences are going to be found, because both immunity and reproduction processes differ according to sex (Schomburg & Schweizer, 2009b).

It has been reported that selenoprotein biosynthesis discriminates among the individual selenoproteins, and impaired selenoprotein biosynthesis becomes phenotypically evident (Schomburg & Schweizer, 2009b). Akbaraly et al.(2010) conducted a study in an elderly French sample, and found that males’ plasma selenium concentrations were significantly associated with a lower risk of developing dysglycemia. On the contrary, no association was found in women, where only high systolic blood pressure, high BMI, alcohol intake, use of lipid-lowering drugs and low HDL cholesterol were related to the incidence of dysglycemia (Akbaraly et al., 2010). As noted above, differences in the pattern of selenoprotein absorption between men and women were observed, suggesting a sexual dysmofirm in the selenium regulation in the body.

Gender specific differences are not yet fully clarified regarding the DM-selenium relationship. In a Cochrane Review including only randomized control trials with healthy adults (1,100,000 from 55 studies), no gender-specific relationship between DM and selenium was found (Vinceti et al., 2015). However, here again the results are not linear. In a study, conducted in three European countries and involving couples to study the differences between genders, it was found that women with metabolic syndrome had increased plasma selenium. This association remains significantly even after adjustments for age, country group, social status, physical activity, energy intake, alcohol consumption, smoking, menopausal status, uses of oral contraceptive pills or hormonal replacement therapy. (Arnaud et al., 2012).

This gender dimorphism has recently been described to happen only in young adults, with differences tending to disappear with advanced age. This study found a high correlation of total selenium and selenium protein P concentrations in young and elderly men, and in elderly women, but not in young women. This result suggests that selenium concentrations and correlations with diseases such as cancer or DM should be done with caution, especially in young women (Hybsier et al., 2017).

The literature is scarce in studies that report the effect of gender as a cofactor in the relationship between DM and selenium. In addition to there being little research in this area, those that exist do not have as main objective this evaluation. The effect of the gender is applied to study models as a possible confounder. As such it may be important to assess the associations of age, selenium and indicators of DM management, being age as a factor that influence these associations.

The literature is not clear, and very scarce in studies that report the effect of age as a factor in the relationship between DM and selenium. Most studies were done in animals and few were applied to human testing. Zelenka and Fajmonova, (2005), conducted a study in chickens, and showed that that selenium concentration in the body increased with age. Richie et al. (2012) conducted similar research in rats to study age related changes in selenium and prostate problems, and their results showed that there is a positive relationship between age and selenium levels, suggesting that this compound may be playing a mechanistic role.

However, and supporting what the animal testing studies indicate, selenium concentrations seem to increase in older human individuals. Recent studies, like the one conducted by Jain and Choi (2015) that included data from Data from National Health and Nutrition Examination Survey for the period 2011–2012, were particularly important to identify the effect of age status on the levels of selenium. Results showed that levels of selenium were lower in adolescents aged 12–19 years than adults aged 20–64 years. Letsiou et al. (2014) study showed no age-related changes in selenium levels in their 400 individuals’ sample.

Older people usually have reduced appetite and energy expenditure, associated with a decline in their biological and physiological functions, such as the loss of lean mass, dysregulation of hormonal levels and cytokines, among others. Selenium is present in several proteins, called selenium-containing proteins. Thus, with a reduction in the intake of certain nutrients, the protein in the elderly is compromised and consequently the ingestion of selenium associated with it. However, these differences within studies may be partially explained because, recently a systematic review found that the ingestion of Se was significantly lower in elderly sarcopenic when compared to nonsarcopenic elderly. These associations may be explained by the potential action of Se on muscle tissue. It is believed that Se may have an effect on muscle synthesis and function through selenoproteins. Due to its cytoprotective properties, it has the ability to upregulate antioxidant selenium enzymes. Therefore, it is believed that with its supplementation can prevent certain metabolic diseases such as DM in elderly.

Chapter 4. RESULTS

Table 1 shows the distribution of the socio-demographic characteristics of the subjects. The majority of the subjects (74.8%) were aged between 40 and 69 years. The percentage of males was almost equivalent to females. In terms of race/ethnicity, the highest percentage was for non-Hispanic Whites, followed by non-Hispanic Blacks, Mexican Americans, Other Hispanics, and then those of other races (multi-racial).

Table 1. Socio-demographic Characteristics

Table 2 illustrates the educational levels, and the annual household incomes of the subjects. Regarding education levels, the largest percentage (48.5%) had educational levels between High school graduate/GED to Some college or AA degree. The annual household income level varied considerably, with the highest percentage of subjects (20.2%) earning annual incomes of $19,999 or less, followed by 17.0% earning $100,000 or more, with the lowest percentage (3.4%) earning $20,000 or more.

Table 2. Socio-economic Characteristics

Tables 3 and 4 indicate that there are no significant differences in selenium intakes by diabetes classification based on A1C or FPG in either gender.

Table 3. Selenium Intake (mcg) by A1C Levels and Gender

1A1C≥6.5% 2A1C≥5.7% &<6.5%) 3A1C<5.7%

aNo significant differences found (p>0.05)

Table 4. Selenium Intake (mcg) by Fasting Plasma Glucose (FPG) Levels and Gender

1FPG≥126.0 mg/dL 2FPG≥100.0 & <126.0 mg/dL 3FPG<100.0 mg/dL

aNo significant differences found (p>0.05)

Table 5 shows serum selenium levels by A1C levels and gender. No significant differences in serum selenium were found among diabetic, prediabetic and nondiabetic females. However, diabetic males had significantly higher serum selenium levels than those who were prediabetic or nondiabetic.

Table 5. Serum Selenium (mcg/L) by A1C Levels and Gender

1A1C≥6.5% 2A1C≥5.7% &<6.5%) 3A1C<5.7%

a,bMeans with different letters as superscript are significantly different (p0.05)

Table 6 shows serum selenium levels by fasting plasma glucose (FPG) levels and gender. No significant differences in serum selenium were found among diabetic, prediabetic and nondiabetic females. However, diabetic males had significantly higher serum selenium levels than those who were prediabetic or nondiabetic.

Table 6. Serum Selenium (mcg/L) by Fasting Plasma Glucose (FPG) Levels

1FPG≥126.0 mg/dL 2FPG≥100.0 & <126.0 mg/dL 3FPG<100.0 mg/dL

a,b,cMeans with different letters as superscript are significantly different (p<0.05)

Table 7 shows selenium intake levels by A1C levels for people with diabetes. No significant differences in selenium intake were found among the group age 40-49 years old. However, the age group from 50-59, 60-69, 70-79, and 80 years old and over had significantly higher selenium levels.

Table 7. Selenium Intake (mcg) by Age in Diabetics Classified on the Basis of A1C Levels1

1A1C≥6.5%

a,bMeans with different letters as superscript are significantly different (p<0.05)

Table 8 shows selenium intake levels by fasting plasma glucose (FPG) levels for people with diabetes. No significant differences in selenium intake were found among the group age 40-49, 60-69, 70-79, and 80 years old and over. However, the age group from 50-59 years old had significantly higher selenium levels.

Table 8. Selenium Intake (mcg) by Age in Diabetics Classified on the Basis of FPG Levels1

1FPG≥126.0 mg/dL

a,bMeans with different letters as superscript are significantly different (p<0.05)

Table 9 shows serum selenium levels by A1C levels for people with diabetes. No significant differences in serum selenium were found among the group age 40-49, 50-59, 60-69, and 80 years and over. However, the age group from 70-79 years old had significantly higher serum selenium levels.

Table 9. Serum Selenium (mcg/L) by Age in Diabetics Classified on the Basis of A1C Levels1

1A1C≥6.5%

a,bMeans with different letters as superscript are significantly different (p<0.05)

Table 10 shows serum selenium levels by fasting plasma glucose (FPG) levels for people with diabetes. No significant differences in serum selenium were found among the group age 40-49, 50-59, and 60-69 years old. However, the age group from 70-79, and 80 years and over had significantly higher serum selenium levels.

Table 10. Serum Selenium (mcg/L) by Age in Diabetics Classified on the Basis of Fasting Plasma Glucose (FPG) Levels1

1FPG≥126.0 mg/dL

a,bMeans with different letters as superscript are significantly different (p<0.05)

guidelines you should read this and based on it you should provide the following;

-general discussion ( compare the results with the literature review ) 4 pg

-conclusion, recommendation of the study and limitation ofthe study 3 pg