Critique

Original Research

Association between Physical Activity and Health-Related Quality of Life in Adults with Type 2 Diabetes

Danielle M. Thiel BSc a, Fatima Al Sayah PhD a, Jeff K. Vallance PhD b, Steven T. Johnson PhD b, Jeffrey A. Johnson PhD a,* a Alliance for Canadian Health Outcomes Research in Diabetes, School of Public Health, University of Alberta, Edmonton, Alberta, Canada b Centre for Nursing and Health Studies, Faculty of Health Disciplines, Athabasca University, Athabasca, Alberta, Canada

a r t i c l e i n f o

Article history: Received 14 April 2016 Received in revised form 18 July 2016 Accepted 18 July 2016

Keywords: health-related quality of life mental health physical activity physical health type 2 diabetes

a b s t r a c t

Objectives: To examine the association between meeting physical-activity recommendations and health- related quality of life (HRQL) in adults with type 2 diabetes. Methods: Data from the Alberta’s Caring for Diabetes cohort were used. Self-report questionnaires were mailed to patients with type 2 diabetes who were living in Alberta, Canada. Weekly moderate-vigorous physical activity (MVPA) was reported using the Godin Leisure Time Physical Activity Questionnaire, and HRQL was reported using the Medical Outcomes Study (MOS) 12-Item Short-Form Health Survey v. 2 (SF-12 v. 2) and the 5-level EuroQol 5-Dimensions (EQ-5D). Based on current guidelines for patients with type 2 diabetes in Canada, participants were grouped according to whether they accrued 150 minutes of MVPA per week. Multivariable linear regression models were used to explore associations between physical activ- ity and HRQL. Results: The mean age of participants (N=1948) was 64.5±10.8, and 45% were female. Participants reported a mean of 84.1±172.4 minutes of MVPA per week, and 21% (n=416) met recommendations for physical activity. Those who met physical activity recommendations reported higher scores on physical function- ing (b=9.58; p<0.001); role-physical (b=8.87; p=0.001); bodily pain (b=5.12; p=0.001); general health (b=6.66; p<0.001); vitality (b=9.05; p<0.001); social functioning (b=3.32; p=0.040); and role-emotional (b=3.08; p=0.010); physical component summary (b=3.31; p<0.001); mental component summary (b=1.43; p=0.001) and EQ-5D-5L index score (b=0.022; p=0.005) compared to those not meeting recommendations. Conclusions: The majority of the sample did not meet the guidelines for physical activity. Among those who did, a significant positive association was observed with HRQL, particularly physical health.

© 2016 Canadian Diabetes Association.

Mots clés : qualité de vie liée à la santé sante mentale activité physique sante physique diabète de type 2

r é s u m é

Objectifs : Examiner l’association entre le respect des recommandations en matière d’activité physique et la qualité de vie liée à la santé (QVLS) chez les adultes souffrant du diabète de type 2. Méthodes : Les données de la cohorte Alberta’s Caring for Diabetes (ABCD) étaient utilisées. Les ques- tionnaires d’auto-évaluation étaient postés aux patients souffrant du diabète de type 2 qui vivaient en Alberta, au Canada. L’activité physique modérée à vigoureuse (APMV) hebdomadaire était rapportée au moyen du questionnaire Godin Leisure-Time Exercise Questionnaire (GLTEQ), et la QVLS était rapportée au moyen de l’enquête Medical Outcomes Study (MOS) 12-Item Short-Form Health Survey v. 2 (SF-12 v. 2) et du questionnaire 5-Level EuroQol 5-Dimensions (EQ-5D-5L). En s’appuyant sur les lignes directrices actuelles concernant les patients souffrant du diabète de type 2 du Canada, les participants étaient regroupés selon qu’ils accumulaient 150 minutes d’APMV par semaine. Les modèles de régression linéaire multivariée étaient utilisés pour étudier les associations entre l’activité physique et la QVLS. Résultats : L’âge moyen des participants (n=1948), dont 45 % étaient des femmes, était de 64,5±10,8 ans. Parmi les participants qui rapportaient une moyenne de 84,1±172,4 minutes d’APMV par semaine, 21 % (n=416) respectaient les recommandations en matière d’activité physique. Ceux qui respectaient les recommandations en matière d’activité physique rapportaient des scores plus élevés de fonctionnement

* Address for correspondence: Jeffrey A. Johnson, PhD, 2-040 Li Ka Shing Centre for Health Research Innovation, School of Public Health, University of Alberta, Edmonton, Alberta T6G 2E1, Canada.

E-mail address: [email protected]

Can J Diabetes 41 (2017) 58–63

Contents lists available at ScienceDirect

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1499-2671 © 2016 Canadian Diabetes Association. http://dx.doi.org/10.1016/j.jcjd.2016.07.004

physique (b=9,58; p<0,001); de limitation physique (b=8,87; p=0,001); de douleur corporelle (b=5,12; p=0,001); de santé générale (b=6,66; p<0,001); de vitalité (b=9,05; p<0,001); de fonctionnement social (b=3,32; p=0,040); de limitation émotionnelle (b=3,08; p=0,010); au sommaire de la composante phy- sique (b=3,31; p<0,001); au sommaire de la composante mentale (b=1,43; p=0,001) et du score indiciel EQ-5D-5L (b=0,022; p=0,005) comparativement à ceux qui ne respectaient pas les recommandations. Conclusions : La majorité de l’échantillon ne respectait pas les lignes directrices en matière d’activité phy- sique. Parmi ceux qui les respectaient, une association positive significative avec la QVLS était observée, particulièrement avec la santé physique.

© 2016 Canadian Diabetes Association.

Introduction

More than 2 million Canadians are currently living with diabe- tes, the vast majority with type 2 diabetes. Diabetes is the seventh leading cause of death in Canada and is a major driver of total healthcare costs (1). If current incidence and mortality trends con- tinue, approximately 3.8 million Canadians will be living with type 2 diabetes by 2018 (1). Because there is currently no cure for the disease, the focus of diabetes care is improving functioning and quality of life while working to minimize the healthcare costs asso- ciated with the disease.

Health-related quality of life (HRQL) is an important outcome in type 2 diabetes research. HRQL is a multidimensional construct that incorporates physical, mental, emotional and social well- being. Research indicates that those with type 2 diabetes typically report diminished HRQL, in part due to the complications and comorbidities that often accompany the disease (2). Additionally, individuals with type 2 diabetes tend to be older and overweight or obese, both of which are associated with lower HRQL (3).

The Canadian Diabetes Association (CDA) recommends at least 150 minutes per week of moderate-vigorous aerobic exercise, such as brisk walking, jogging or biking plus at least 2 sessions per week of resistance exercise (4). Despite these recommendations, many Canadians with type 2 diabetes are sedentary or insufficiently active (5). Previous research has demonstrated a positive relationship between physical activity and HRQL in the general adult popula- tion (6). Some studies suggest that this relationship holds true in populations with type 2 diabetes; however, some randomized con- trolled trials have indicated that participation in aerobic physical- activity programs did not result in improved physical or mental health scores (3,7–9). Therefore, more research is required for better understanding of the relationship between physical activity and HRQL in this population.

The aim of this study was to examine the differences in HRQL between patients with type 2 diabetes who meet the CDA recom- mendations for physical activity compared with those who do not. We hypothesized that people who meet recommendations for physi- cal activity will have better HRQLs than those who do not. Addi- tionally, we sought to investigate whether exceeding the baseline recommendations (≥300 moderate-vigorous physical activity [MVPA] minutes per week) was associated with better HRQL in patients with type 2 diabetes compared to meeting baseline recommendations.

Methods

Data source

This study used baseline data from the Alberta Caring for Dia- betes (ABCD) cohort study, which has been described elsewhere (10). Briefly, English-speaking individuals with type 2 diabetes who were living in Alberta and were older than 18 years of age were eligible to participate. Participants were recruited over a 2-year period (December 2011 to December 2013) through primary care net- works and diabetes clinics as well as public advertisements. Those

who agreed to participate were mailed self-administered surveys, which contained various items and measures that have been devel- oped, validated and used in previous studies of populations with diabetes. Surveys included information about disease manage- ment, health and lifestyle, HRQL, emotional and psychosocial well- being and sociodemographics. The sample was considered to be generally representative of the adult population with type 2 dia- betes in Alberta (10).

Physical activity

Physical activity was assessed using the Godin Leisure Time Physi- cal Activity Questionnaire (GLTEQ) (11). Participants were asked to report the frequency and duration of light-intensity (easy walking, yoga, golf); moderate-intensity (brisk walking, easy bicycling, tennis); and vigorous-intensity (aerobics, jogging, swimming laps) leisure- time physical activity performed in a typical week. The number of weekly minutes was calculated by multiplying the frequency of physical activity by the duration in minutes. The sum of the unweighted weekly minutes of moderate and vigorous physical activ- ity gave the total MVPA minutes per week.

Health-related quality of life

HRQL was assessed using both the Medical Outcomes Study (MOS) 12-Item Short-Form Health Survey version 2 (SF-12) and the 5-level EuroQol 5-Dimensions (EQ-5D-5L) questionnaire. The SF-12 is a condensed 12-item version of the SF-36, a commonly used generic health-status tool. An 8-dimension profile (physical func- tioning, role limitations due to physical problems, bodily pain, general health, vitality, limitations due to emotional problems and mental health) is created, from which physical and mental component summary scores (PCS, MCS) are derived. This study used scoring coefficients from oblique factor analysis (12). SF-12 summary scores follow a T distribution with a mean of 50 and a standard devia- tion of 10, which is normalized for the general United States popu- lation. Thus, observed scores can be interpreted as deviations from the norm, with lower scores on the PCS and MCS indicating greater disability (13). For domain and summary scores, a clinically impor- tant difference is in the range of 3 to 5 points (14).

The EQ-5D-5L is a preference-based health status measure con- sisting of 5 dimensions (mobility, self-care, usual activities, pain or discomfort and anxiety or depression), each with 5 levels (no prob- lems, mild problems, moderate problems, severe problems, extreme problems), which yield a single index score (15). The index score was calculated using a scoring function derived from Canadian pref- erences (16). Each described health state has a unique score, anchored at 0.0 for “dead” and 1.0 for “full health,” with higher scores indicating better HRQL. A clinically important difference on this scale is 0.03 points (17).

Other measures

Data on age; sex; ethnicity (white, Aboriginal, other); annual household income in Canadian dollars (<$80 000 or ≥$80 000); level of education (less than high school, high school, more than high

D.M. Thiel et al. / Can J Diabetes 41 (2017) 58–63 59

school); employment status (employed; not employed); family history of diabetes (yes, no); smoking status; diabetes duration; number of comorbidities (of 16 common diabetes comorbidities); and depressive symptoms (using the Patient Health Questionnaire-8 items (PHQ-8) were also collected (18).

Statistical analyses

CDA guidelines were used to categorize participants based on their physical activity into 2 levels:

• Those who did not meet recommendations: <150 MVPA min/week

• Those who did meet recommendations: ≥150 MVPA min/week

A secondary analysis included 3 levels:

• Those who did not meet recommendations: <150 MVPA min/week

• Those who met the baseline recommendations: 150 to 299.9 MVPA min/week

• Those who exceeded the baseline recommendations: ≥300 MVPA min/week.

Descriptive statistics were computed for all variables in the overall sample and by physical activity level. Differences were tested using the t test or the chi-square test, as appropriate. Univariable analy- ses were performed to determine associations between physical activity and HRQL indicators. The association of possible covariates was tested using simple linear regression, and variables were included in the final model if they were significant in univariable analysis or if they have been shown to be clinically relevant in other studies. In this study, these included the categorical variables of income, number of comorbidities (0, 1 or ≥2), depressive symp- toms, and smoking status as well as age and duration of diabetes as continuous variables. Multivariable linear regression was used to examine differences among groups in each HRQL indicator. Unstandardized beta coefficients were interpreted by both statis- tical significance and clinical importance. All final model assump- tions were checked. Statistical inferences were based on a significance level of p<0.05 (2-sided). The data were analyzed using Stata 13.1 for Mac (Stata Corp, College Station, Texas, USA).

Results

General characteristics of participants

Of the full cohort, 92 individuals received slightly different ver- sions of the HRQL measures and thus were excluded from this study. The average age of participants (N=1948) was 64.5±10.8; 45% were female, and 91% were white. The majority of participants had at least high school educations and household incomes of less than $80 000. On average, participants had lived with diabetes for 12.6±10 years and had an average of 4.2±2.3 comorbidities in addition to diabe- tes. Participants reported a mean EQ-5D index score of 0.79±0.17, a mean PCS of 44.2±10.8 and a mean MCS of 48.9±9.8 (Table 1), sug- gesting that their health statuses were slightly lower than average when compared with population norms (i.e. a mean PCS/MCS of 50.0).

The majority (n=1532; 78.6%) of participants did not meet physi- cal activity recommendations, with a mean duration of 84.1±172.4 minutes of MVPA per week. Participants who did not meet recom- mendations were more likely to have less education, be smokers, have more comorbidities and report more depressive symptoms (Table 1). Participants who exceeded the base recommendations for

physical activity (≥300 MVPA min per week) (n=167) were more likely to be male, earn more than $80 000, have more than a high school education, have fewer comorbidities and be less likely to be depressed (Table 1).

Physical activity and HRQL indicators

After adjustment for age, sex, income, smoking status, number of comorbidities, diabetes duration and depressive symptoms, mul- tivariable regression analyses revealed differences in HRQL between those who met the CDA recommendations and those who did not (Table 2). Those who met recommendations reported higher HRQL scores in the physical functioning (b=9.58; p<0.001); role-physical (b=8.87; p=0.001); bodily pain (b=5.12; p=0.001); general health (b=6.66; p<0.001); vitality (b=9.05; p<0.001); social functioning (b=3.32; p=0.040); and role-emotional (b=3.08; p=0.010) domains when compared with those who did not meet recommendations. The PCS scores (b=3.31; p<0.001); MCS scores (b=1.43; p=0.001); and EQ-5D-5L index scores (b=0.022; p=0.005) were also strongly associated with physical activity when the

Table 1 Characteristics of participants

Met PA recommendations

Characteristic Overall (N=1948) mean ± SD or N(%)

Yes (n=416) mean ± SD or n (%)

No (n=1532) mean ± SD or n (%)

p value

Female sex 875 (45.2) 158 (38.0) 717 (46.8) 0.001 Age (years) 64.5±10.8 63.4±10.3 64.9±10.9 0.013 Annual household income* 0.012 <$80 000 1122 (57.6) 228 (54.8) 894 (58.4) ≥$80 000 454 (23.3) 119 (28.6) 335 (21.9)

Education <0.001 Less than high school 275 (14.1) 37 (8.9) 238 (15.5) Completed high school 780 (40.0) 139 (33.4) 641 (41.8) More than high school 881 (45.2) 250 (57.7) 641 (41.8)

Employment status: unemployed/retired

1127 (58.8) 238 (57.9) 889 (59.0) 0.682

Ethnicity 0.448 White 1765 (90.6) 379 (91.1) 1386 (90.5) Aboriginal 46 (2.4) 8 (1.9) 38 (2.5) Other 106 (5.4) 27 (6.5) 79 (5.2)

Current smoker 199 (10.2) 28 (6.7) 171 (11.2) 0.008 Diabetes duration (years) 12.6±10.0 12.0±9.5 12.8±10.2 0.262 Number of comorbidities 4.2±2.3 3.5±2.1 4.4±2.3 <0.001 Depressive symptoms 5.2±5.4 3.7±4.7 5.6±5.5 <0.001 No (PHQ-8<10) 1532 (78.6) 366 (88.0) 1166 (76.1) Yes (PHQ-8≥10) 416 (21.4) 50 (12.0) 366 (23.9)

HRQL indicators EQ-5D-5L Mobility 1030 (52.9) 151 (36.4) 879 (58.0) <0.001 Self-care 223 (11.5) 26 (6.3) 197 (12.9) <0.001 Usual activities 928 (47.6) 123 (29.6) 805 (52.6) <0.001 Pain/discomfort 1431 (73.5) 269 (64.7) 1162 (75.9) <0.001 Anxiety/depression 905 (46.5) 169 (40.6) 736 (48.0) 0.004 Index score 0.79±0.17 0.84±0.13 0.78±0.18 <0.001

SF-12 indicators Physical functioning 66.3±34.8 80.7±29.1 62.3±35.2 <0.001 Role-physical 65.8±30.2 78.7±25.7 62.3±30.4 <0.001 Bodily pain 67.5±30.7 76.5±27.3 65.1±31.1 <0.001 General health 60.9±24.0 70.2±19.7 58.4±24.4 <0.001 Vitality 53.0±24.8 63.7±23.0 50.1±24.4 <0.001 Role-emotional 77.9±25.5 84.8±21.5 76.0±26.1 <0.001 Social functioning 76.1±28.2 84.0±24.9 73.9±28.6 <0.001 Mental health 71.1±20.6 74.6±20.0 70.1±20.7 <0.001 PCS 44.2±10.8 49.1±9.0 42.9±10.9 <0.001 MCS 48.9±9.8 50.7±9.3 47.1±9.8 <0.001

HRQL, health-related quality of life; MCS, mental component summary score; PA, physical activity; PCS, physical component summary score; SD, standard deviation. Notes: Data are presented as mean (SD) for continuous variables and frequency (%) for categorical variables. Numbers may not add up to 1948 due to missing data. * Canadian dollars.

D.M. Thiel et al. / Can J Diabetes 41 (2017) 58–6360

meeting-recommendations group was compared to the not-meeting- recommendations group.

Those who exceeded the recommended amount of physical activ- ity (≥300 MPVA min per week) reported higher HRQL scores than those who did not achieve physical activity recommendations (Table 3). Differences in the physical functioning (b=14.68; p<0.001); role-physical (b=12.13; p<0.001); bodily pain (b=5.66; p=0.018); general health (b=9.62; p<0.001) and vitality (b=12.13; p<0.001) dimensions were statistically significant, as were differences in the PCS (b=4.64; p<0.001); MCS (b=1.76; p=0.006) and EQ-5D index scores (b=0.035; p=0.003). When comparing those who exceeded recommendations (≥300 MPVA min per week) to those who met the baseline recommendations (150 to 299.9 MVPA min per week), no significant differences in any HRQL parameters were found (Table 3).

Discussion

The aim of this study was to examine the association between meeting CDA recommendations for physical activity and HRQL among adults with type 2 diabetes who were living in Alberta. Overall, the results confirmed our hypothesis—that meeting the CDA recommendations for physical activity would be associated with better HRQL when compared with not meeting recommenda- tions. These associations persisted after adjustment for relevant demographic and clinical variables. Specifically, meeting recom- mendations was associated with higher scores in the physical func- tioning, role-physical, bodily pain, general health, vitality, social functioning and mental health dimensions. Moreover, the observed differences were meaningful, based on guidelines for minimal impor- tant differences. A 3- to 5-point difference is considered clinically important in the SF-12 domains, and the difference between the group who met recommendations and the group who did not exceeded this difference in the dimensions related to physical health (i.e. physical functioning, role-physical, bodily pain, general health and vitality). When considering mental health or overall HRQL, the relationship is not as strong, and differences were not considered clinically important.

The results from this study are generally consistent with pre- vious research, which indicates positive associations between physical activity and HRQL. In healthy adults, those who attain

recommended levels of physical activity have previously reported higher scores on the physical functioning, general health and vital- ity dimensions as well as on the PCS (19,20). In diabetes-specific populations, HRQL has been found, in other cross-sectional studies, to decrease with decreasing levels of physical activity (8,9). The results from this study contribute to this body of knowledge by pro- viding evidence from a large population-based cohort of patients with type 2 diabetes. Additionally, this study used current clinical practice guidelines to categorize participants into physical activ- ity groups so as to assess the difference in HRQL between those who were meeting the guidelines and those who were not.

In general, these study results also confirm previous research that indicates that the physical aspects of HRQL are more closely asso- ciated with physical activity than the mental aspects (21–23).

Table 2 Results of adjusted multivariable linear regression models of the relationship between meeting guidelines for PA (2 categories) and HRQL

HRQL indicator Met PA recommendations b SE p value

Yes (n=416) mean ± SE

No (n=1532) mean ± SE

SF-12 Physical functioning 73.92±1.45 64.33±0.75 9.58 1.64 <0.001 Role-physical 72.85±1.24 63.98±0.64 8.87 1.41 <0.001 Bodily pain 71.56±1.39 66.44±0.71 5.12 1.57 0.001 General health 66.36±1.03 59.69±0.53 6.66 1.17 <0.001 Vitality 60.23±1.07 51.18±0.56 9.05 1.22 <0.001 Role-emotional 80.41±1.05 77.33±0.55 3.08 1.20 0.010 Social functioning 78.65±1.14 75.32±0.59 3.32 1.29 0.010 Mental health 71.97±0.88 70.90±0.45 1.06 0.99 0.284 PCS 46.81±0.42 43.50±0.22 3.31 0.48 <0.001 MCS 48.97±0.38 47.54±0.20 1.43 0.43 0.001 EQ-5D-5L Index score 0.81±0.007 0.79±0.003 0.022 0.007 0.005

b, beta coefficient; EQ-5D-5L, EuroQol 5-Dimensions; HRQL, health-related quality of life; MCS, mental component summary score; PA, physical activity; PCS, physical component summary score; SD, standard deviation; SE, standard error; SF-12, 12-Item Short-Form Health Survey, version 2. Note: Reference: group not meeting recommendations (<150 min of moderate- vigorous physical activity per week).

Table 3 Results of adjusted multivariable linear regression models of the relationship between meeting guidelines for PA (3 categories) and HRQL*

HRQL indicator Adjusted score mean ± SE

b SE p value

SF-12 Physical functioning Not meeting recommendations (Ref) 63.73±0.81 Meeting recommendations 74.47±2.00 10.74 2.16 <0.001 Exceeding recommendations 78.42±2.41 14.68 2.56 <0.001 Role-physical Not meeting recommendations (Ref) 63.52±0.68 Meeting recommendations 73.71±1.69 10.19 1.83 <0.001 Exceeding recommendations 75.65±2.96 12.13 2.18 <0.001 Bodily pain Not meeting recommendations (Ref) 66.08±0.74 Meeting recommendations 73.69±1.84 7.61 1.99 <0.001 Exceeding recommendations 71.74±2.25 5.66 2.39 0.018 General health Not meeting recommendations (Ref) 59.40±0.56 Meeting recommendations 66.36±1.38 6.96 1.50 <0.001 Exceeding recommendations 69.02±1.68 9.62 1.78 <0.001 Vitality Not meeting recommendations (Ref) 50.88±0.58 Meeting recommendations 60.16±1.42 9.28 1.54 <0.001 Exceeding recommendations 63.01±1.74 12.13 1.84 <0.001 Role-emotional Not meeting recommendations (Ref) 77.14±0.55 Meeting recommendations 81.66±1.37 4.52 1.48 0.002 Exceeding recommendations 80.29±1.67 3.15 1.76 0.074 Social functioning Not meeting recommendations (Ref) 75.10±0.60 Meeting recommendations 81.52±1.48 6.52 1.60 <0.001 Exceeding recommendations 76.41±1.81 1.31 1.91 0.495 Mental health Not meeting recommendations (Ref) 70.72±0.46 Meeting recommendations 72.59±1.13 1.83 1.22 0.135 Exceeding recommendations 72.29±1.38 1.53 1.46 0.295 PCS Not meeting recommendations (Ref) 43.32±0.24 Meeting recommendations 47.10±0.59 3.77 0.64 <0.001 Exceeding recommendations 47.96±0.71 4.64 0.75 <0.001 MCS Not meeting recommendations (Ref) 47.45±0.20 Meeting recommendations 49.35±0.50 1.90 0.54 <0.001 Exceeding recommendations 40.20±0.61 1.76 0.64 0.006 EQ-5D-5L index score Not meeting recommendations (Ref) 0.78±0.004 Meeting recommendations 0.82±0.009 0.032 0.0010 0.001 Exceeding recommendations 0.82±0.011 0.035 0.012 0.003

b, beta coefficient; EQ-5D-5L, EuroQol 5-Dimensions; HRQL, health-related quality of life; MCS, mental component summary score; MVPA, moderate-vigorous physi- cal activity; PA, physical activity; PCS, physical component summary score; SD, stan- dard deviation; SE, standard error; SF-12, 12-Item Short-Form Health Survey, v. 2. Notes: Reference: Not meeting recommendations (<150 min of MVPA per week); meeting recommendations (150 to 299.9 min of MVPA per week); exceeding rec- ommendations (≥300 min of MVPA per week). * Differences between the meeting-recommendations group and the exceeding-

recommendations group were not statistically significant on any HRQL indicator.

D.M. Thiel et al. / Can J Diabetes 41 (2017) 58–63 61

Vitality is classified as a mental health dimension but seeks to measure the level of energy, pep or tiredness experienced and is moderately correlated with both mental and physical functioning (13). The relationship between physical activity and the mental com- ponents of HRQL are not entirely clear. Given the prevalence of mental disorders in people with diabetes, there are likely to be many factors that influence the relationship between physical activity and HRQL in patients with type 2 diabetes. Most likely, a bidirectional relationship between physical activity and HRQL exists, whereby those individuals who perceive themselves as having better physi- cal and mental health are more likely to participate in physical activ- ity. Due to the cross-sectional nature of this study, we were unable to draw a conclusion about the direction of this relationship.

Despite evidence that participation in physical activity is asso- ciated with better HRQL, the majority of participants (78%) did not meet current recommendations, which is consistent with similar studies in this population (5). Despite the existence of clinical guide- lines that seek to educate patients with diabetes about the impor- tance of physical activity, it is challenging to motivate individuals to make lifestyle modifications and maintain new habits (9). The results of this study provide more evidence that there are signifi- cant associations between meeting the current clinical practice guidelines for physical activity and better HRQL in this patient population.

The U. S. Department of Health and Human Services suggests that additional health benefits can be accrued by achieving at least 300 minutes per week of moderate-vigorous physical activity (24). We sought to investigate whether there was an association between higher levels of physical activity and HRQL in individuals with type 2 diabetes. Those individuals who exceeded the baseline recommen- dations (≥300 MPVA min per week) reported higher HRQL scores across all dimensions than did those who did not meet the base- line recommendations (<150 MVPA min per week). The differ- ences in HRQL between those who exceeded recommendations and those who did not meet recommendations were larger than the dif- ferences between those who met baseline recommendations and those who did not in the physical functioning, role-physical, general health and vitality dimensions, as well as on the PCS. These results suggest that an association exists between achieving more than 300 minutes of MVPA per week and higher HRQL in dimensions related to physical health. Differences between those who met baseline rec- ommendations and those who exceeded baseline recommenda- tions were not statistically significant; however, this may have been due to a lack of statistical power to detect differences. Previous studies in both the general population and in community-dwelling older adults have demonstrated similar associations between higher levels of physical activity and HRQL but there is little evidence to date concerning this relationship in type 2 diabetes (6,25–27).

The strengths of this study include the use of a large, population- based cohort that is representative of the population with type 2 diabetes in Alberta, based on estimates from the Alberta Diabetes Surveillance System as well as the use of validated questionnaires and multiple indicators of HRQL (10). Nonetheless, the results should be interpreted in light of a few limitations. First, the use of cross- sectional data precluded us from establishing temporality or cau- sality. We found a positive association between physical activity and HRQL, but we were unable to confirm the direction of this asso- ciation. Second, data were collected using self-reported question- naires. In particular, the use of the GLTEQ for self-reported physical activity could have led to overestimates (28). Accelerometer data have been collected in a subset of this cohort and could be used in a future study to assess the validity of the self-reported ques- tionnaire in this population. Additionally, the GLTEQ assesses only leisure-time physical activity, so physical activity associated with work was not captured in this study. Third, we did not have a measure dedicated to resistance exercise and, therefore, it is

impossible to know whether those meeting recommendations for aerobic exercise were also meeting recommendations for resis- tance exercise or whether that would impact HRQL. Finally, although we adjusted for several variables that might be associated with physi- cal activity and HRQL, we cannot rule out that there could be other factors (including physical injury, access to facilities, medications and other habits related to health) that might have impacted this relationship.

Conclusions

In summary, the findings in this study indicate that individuals with type 2 diabetes who meet recommendations for physical activ- ity report better HRQL compared with those who do not. Meeting recommendations for physical activity is more strongly related to physical health than to mental health. Our findings also suggested that there may be an association between higher weekly levels of physical activity and the physical components of HRQL in this popu- lation. This suggests that individuals with type 2 diabetes who are capable of exceeding the recommended amount of physical activ- ity may experience better HRQL in dimensions related to physical health than those who simply meet the baseline recommenda- tions. To better assess this relationship, both longitudinal and experi- mental studies are needed to determine whether changes in physical activity are associated with changes in HRQL. Additionally, only 21.5% of the sample reported physical activity levels that were congru- ent with the recommendations set forth by the CDA, indicating that public health efforts to promote physical activity and decrease sed- entary lifestyle habits must be continued in order to improve care and health outcomes for patients with type 2 diabetes.

Acknowledgments

This work was supported in part by a grant from Alberta Health and a CIHR Team Grant to the Alliance for Canadian Health Out- comes Research in Diabetes (#OTG- 88588), sponsored by the CIHR Institute of Nutrition, Metabolism and Diabetes (INMD). DT was sup- ported by a studentship from the Alberta Diabetes Institute. JAJ is a Senior Scholar with Alberta Innovates-Health Solutions (AIHS) and a Centennial Professor at the University of Alberta. JV is sup- ported by the Canada Research Chairs Program and an Alberta Innovates-Health Solutions Population Health Investigator Award.

Author Contributions

DMT and JAJ conceived the study; DMT conducted the analysis and wrote the first draft of the manuscript; all authors provided feedback and approved the final version. JJ is the guarantor and takes full responsibility for the contents of this article.

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