Abstract
In this study, the relationship between physical activity (PA) and 3 self-concept constructs (physical abilities, physical appearance, and general self-concept) was examined. Youth with type 1 diabetes (n=304), type 2 diabetes (n=49), and non-diabetic controls (n=127) aged 10-20 years wore pedometers over 7 days. Youth completed the Self-Description Questionnaire and correlation coefficients were calculated. Mean steps/day were 7413 ± 3415, 4959 ± 3474 and 6870 ± 3521 for type 1, type 2 and control youth, respectively. Significant correlations were found between steps/day and perception of physical abilities (r=0.29; r=0.31; r=0.31) for type 1, type 2, and control youth, respectively. The other correlations were not significant. Among youth with type 2 diabetes, steps/day were significantly correlated with physical appearance (r=0.46). The positive correlation between PA and physical abilities suggests a reciprocal relationship between behavior and perception.
Keywords: physical activity, diabetes mellitus, pedometer, obesity, children, adolescents
Introduction
Diabetes is a serious public health problem for children and adolescents. The SEARCH for Diabetes Study Group estimated the prevalence of diabetes in American youth to be 1.82 cases per 1,000 youth (21). Although type 1 diabetes is more prevalent than type 2 diabetes among most racial and ethnic groups, the opposite is true for American Indian youth (21). The important role of physical activity in the prevention and treatment of diabetes is well known (2,12). Regular physical activity can improve metabolic profiles (31), glucose control and reduce the complications of diabetes (2,12). The majority of children and adolescents do not meet the current physical activity guidelines (27). This is true as well for youth with diabetes, as we have previously shown using a self-reported measure of physical activity (15). Despite the impact of regular physical activity on the treatment of diabetes, little is known about the correlates of physical activity behavior among children and adolescents with type 1 and type 2 diabetes.
In general, physical activity is thought to be influenced by multiple underlying psychological constructs (20). Examples of these constructs include self-efficacy (20), social support (20), and general self-concept (17). General self-concept, as defined by Marsh, encompasses many constructs (17), two of which are physical abilities (11) and physical appearance (16). While a significant body of evidence has emerged that suggests a relationship between psychological constructs and behavior in adults, there is limited data in children and adolescents (20). To date, the relationships between physical activity and the constructs of physical abilities, physical appearance, and general self-concept have not, to our knowledge, been examined among children and adolescents with type 1 and type 2 diabetes. Understanding these relationships will aid in the development of interventions.
The purpose of this paper is to examine the relationship between objectively measured physical activity and three self-concept constructs (17) among youth with and without diabetes. We hypothesize that youth with higher levels of the three self-concept constructs (physical abilities, physical appearance, and general self-concept) will have higher levels of physical activity compared to youth with lower levels of the self-concept constructs, within categories of Type 1, Type 2, and control youth.
Methods
Study Design
The SEARCH for Diabetes in Youth Case-Control (SEARCH CC) Study was an ancillary study conducted at two of the six SEARCH for Diabetes in Youth Study clinical sites. The SEARCH for Diabetes in Youth Study is a multicenter study conducting population-based ascertainment of physician-diagnosed diabetes in youth with onset <20 years of age (21,35). A detailed description of SEARCH study methods has been published elsewhere (22,35). The SEARCH CC Study was designed to evaluate the risk factors for childhood diabetes and associated health status in youth with diabetes compared to non-diabetic controls at the Colorado and South Carolina SEARCH sites.
Participants
Diabetes cases were identified using a network of health care providers. All adolescents 10 years of age or older who participated in the SEARCH study between July 2003 and March 2006 were invited to participate in SEARCH CC. Diabetes type was ascertained by health care providers. Youth with type 1, type 1A, and type 1B were classified as having type 1 diabetes while all youth with type 2 diabetes were categorized as such. Youth with hybrid type, maturity onset of diabetes in youth, unknown, or other types of diabetes were excluded. Overall, 53% of those invited participated in SEARCH CC.
Because all SEARCH cases arose from health care provider offices, we recruited control youth from primary care offices in the same geographic areas. Control recruitment was designed to sample youth based on the distribution of age, sex, and race/ethnicity background of registered cases. Primary care offices provided a study brochure, and patients and their parent or guardian were asked to complete a one-page form that included demographic information and an indication of permission for study staff to contact them regarding participation in the study. The SEARCH CC staff then contacted those interested and recruited participants accordingly. All control youth were confirmed to be nondiabetic by fasting glucose values. Overall, 49% of the youth invited to be controls participated in SEARCH CC.
The study was reviewed and approved by the local institutional review boards. Written informed consent was obtained from all participants, from individuals who were ≥ 18 years of age or from parents or guardians for participants who were < 18 years of age. Written assent was obtained from individuals who were < 18 years of age.
Physical Activity Assessment
Pedometers (Yamax, Japan) were used to objectively measure the number of steps taken over a period of seven consecutive days. Participants received the pedometers and instructions during their clinic visit and were instructed to wear it all day, except when sleeping, swimming, or bathing, and to record the time they began wearing the pedometer and the time they removed it. At the end of each day, they recorded the day of the week and the number of steps and then reset the pedometer to zero. For each day, participants reported if they were sick or injured; those days were excluded from analyses. At the end of the seven-day period, participants returned their record sheets by mail. Non-responders were mailed reminders. Participants did not report if the measured days were school days, holidays, or if they included participation in physical education class. However, the days in which the pedometers were worn were evenly distributed across weekdays and weekend days.
In accordance with guidelines for the analysis of pedometer data (9,14,19), a valid day of pedometer data was one where at least 1,000 steps but less than 30,000 steps were recorded. Reliability increases with the number of measurement days increases. Vincent and Pangrazi (33) reported reliability of 0.70 for three days, and in another study they reported reliability of 0.80 for five days (34). Therefore, for inclusion in this study, participants were required to have at least three valid days of pedometer data. The mean number of steps per day was calculated for each participant.
Self-Concept Assessment
Self-concept was measured with the Marsh Self-Description Questionnaires, (SDQ-I, SDQ-II, SDQ-III) (17). The numerals I, II, and III refer to age-group specific questionnaire versions, as questionnaires were administered to 10- to 12-year-olds, 13- to 15-year-olds, and youth ≥ 16 years of age, respectively. Participants received the SDQ during their clinic visit (along with the pedometer), completed the questionnaire at home, and returned it by mail. The Self-Description Questionnaires assessed several self-concept constructs. The constructs of interest for this study were physical abilities, physical appearance, and general self-concept, each corresponding to a subscale score within the SDQ. The physical abilities scale measures the perception of one’s abilities in performing physical activities, sports, and games; the physical appearance scale measures one’s perception of his/her attractiveness as compared to others, and the perceptions of how others view him or her; and general self-concept refers to the perception of one’s self as an ‘effective, capable individual, proud of and satisfied with the way he or she is’ (17). Responses to each question were reported on a 5-point Likert scale. The numeric values for each response were summed and the scores were converted to population T-scores, with a mean of 50 and a standard deviation of 10, for each subscale. The alpha reliability coefficients for the instruments ranged from 0.83-0.91 (SDQ-I), 0.83-0.91 (SDQ-II), and 0.76-0.95 (SDQ-III), exceeding the 0.70 threshold for scale reliability.
Assessment of Covariates
Standardized physical examinations were conducted by trained and certified study staff members. Height was measured in centimeters using a stadiometer. Weight was measured in kilograms using an electronic scale. Height and weight measurements were used to calculate body mass index (BMI, kg/m2). Age and sex specific BMI z-scores were derived based on the Centers for Disease Control and Prevention national standards (13). Age, race/ethnicity, parental education, diabetes duration and insulin use were assessed by self-report. The season of data collection was determined by the date of the clinic visit.
Statistical Analyses
A total of 892 youth participated in SEARCH CC, and of these youth, 57% had at least three valid days of pedometer data (N = 511). Within this sample, 31 participants (6%) were excluded because they did not have complete SDQ data. Thus, the analytic sample consisted of 480 youth: 304 with type 1 diabetes, 49 with type 2 diabetes, and 127 controls. Participants included did not differ from those excluded among youth with type 1 and type 2 diabetes. Among controls, the only appreciable difference was a greater proportion of excluded youth from Colorado (70.5%), compared to 49.6% of included youth (p < .01).
Because there were three age-group specific versions of the Self-Description Questionnaires, psychometric analyses were conducted to determine whether subsequent analyses could be analyzed on the total sample, or required age stratification. Measures of central tendency were calculated for each of the three constructs and the correlations of the constructs were examined across age groups for comparability. The results demonstrated comparable scores across age groups, indicating that conversion to population T-scores successfully standardized the scores across versions. Therefore, all analyses were conducted with combined age groups.
Descriptive statistics of the self-concept scores (physical appearance, physical abilities, and general self-concept) were calculated by diabetes status (type 1, type 2, and controls). Spearman correlation coefficients and p-values were calculated between the self-concept scores and steps per day by diabetes status. After the crude analyses, adjustments were made for age, sex, race/ethnicity, study site, and season. In a subsequent step we additionally adjusted for parental education, insulin use, diabetes duration, BMI z-score, and comorbidities using partial correlation coefficients.
Results
The sample was 44.2% male and the mean age was 14.7 ± 3.1 years. The majority of the sample was non-Hispanic white (69.8%); 19.6% of youth were African American and 10.6% of youth were Hispanic. Mean steps per day for the total sample were 7019 ± 3519. Mean scores for the self-concept constructs were 49.6 ± 11.0, 53.8 ± 9.8 and 53.8 ± 9.9 for physical abilities subscale, physical appearance subscale, and general self-concept subscale, respectively. Youth with type 1 diabetes were more likely to be male, white, have parents with higher education, and have lower BMI than youth with type 2 diabetes and controls (Table 1). Mean steps per day were 7413 ± 3415, 4959 ± 3474, and 6870 ± 3521 for type 1, type 2 and control youth, respectively (Table 2). There was no difference in steps per day between youth with type 1 diabetes and controls (p = .14). However, both youth with type 1 diabetes and controls obtained significantly more steps per day than youth with type 2 diabetes (p < .05). Males accumulated more steps per day than females (7989 ± 3598 vs. 6252 ± 3264), and non-Hispanic white youth had more steps per day (7431 ± 3416) than Hispanic (7031 ± 3848) and African American youth (5544 ± 3334). The days in which the pedometers were worn were evenly distributed across weekdays and weekend days.
Table 1.
Demographic and clinical characteristics of the SEARCH-CC study sample (N=480)
| Type 1 (n = 304) | Type 2 (n = 49) | Controls (n = 127) | ||||
|---|---|---|---|---|---|---|
| n | % | n | % | n | % | |
| Male a | 150 | 49.3% | 12 | 24.5% | 50 | 39.4% |
| Age, years, M (SD) b | 304 | 14.7 ± 3.2 | 49 | 15.6 ± 2.9 | 127 | 14.5 ± 2.9 |
| Race/ethnicity c | ||||||
| Non-Hispanic White | 249 | 81.9% | 14 | 28.6% | 72 | 56.7% |
| African American | 26 | 8.6% | 29 | 59.2% | 39 | 30.7% |
| Hispanic | 29 | 9.5% | 6 | 12.2% | 16 | 12.6% |
| SEARCH site c | ||||||
| Colorado | 221 | 72.7% | 12 | 24.5% | 63 | 49.6% |
| South Carolina | 83 | 27.3% | 37 | 75.5% | 64 | 50.4% |
| BMI (kg/m2) c | 299 | 21.9 ± 4.3 | 46 | 34.1 ± 8.1 | 126 | 23.5 ± 6.3 |
| BMI z-score d | 299 | 0.53 ± 0.91 | 46 | 1.99 ± 0.76 | 126 | 0.68 ± 1.11 |
| Any comorbidity (%) e | 28 | 9.2% | 1 | 2.0% | 3 | 2.4% |
| Duration of diabetes (years) a | 304 | 4.0 ± 4.3 | 48 | 1.4 ± 1.4 | j | j |
| Parental Education f | ||||||
| < High School | 63 | 20.7% | 27 | 55.1% | 49 | 38.9% |
| High School Grad/GED | 47 | 15.5% | 7 | 14.3% | 14 | 11.0% |
| Some College | 175 | 57.6% | 14 | 28.6% | 53 | 42.1% |
| ≥ Bachelor Degree | 19 | 6.3% | 1 | 2.0% | 10 | 7.9% |
| Insulin Use a | 301 | 99.0% | 17 | 34.7% | 0 | 0.0% |
| Physical Activity | n | M ± SD | n | M ± SD | n | M ± SD |
| Steps per day g | 304 | 7413 ± 3415 | 49 | 4959 ± 3474 | 127 | 6870 ± 3521 |
| Self-Concept Constructs h | n | M ± SD | n | M ± SD | n | M ± SD |
| Physical Abilities g | 304 | 50.5 ± 10.8 | 49 | 44.2 ± 12.3 | 127 | 49.4 ± 10.3 |
| Physical Appearance a | 304 | 54.2 ± 9.3 | 49 | 50.2 ± 12.8 | 127 | 54.1 ± 9.5 |
| General Self-concept i | 304 | 54.3 ± 9.7 | 49 | 51.0 ± 14.4 | 127 | 53.8 ± 8.0 |
T1 > T2, P < .05
T2 > Controls, P = .02
All groups differ, P ≤ .01
T2 > T1, T2 > Controls, P <.001
T1 > Controls, P = .01
T1 > T2, P < .001; T1 > Controls, P < .001
T1 > T2, Controls > T2, P < .05
Population T scores
No differences between groups
Not Applicable
Table 2.
Steps per day among youth with Type 1, Type 2, and Controls by demographic characteristics (N = 480)
| Type 1 a | Type 2 b | Controls c | ||||
|---|---|---|---|---|---|---|
| n | M ± SD | n | M ± SD | n | M ± SD | |
| Sex | ||||||
| Female d | 154 | 6773 ± 2986 | 37 | 4565 ± 3633 | 77 | 6021 ± 3351 |
| Male f | 150 | 8071 ± 3702 | 12 | 6175 ± 2708 | 50 | 8179 ± 3403 |
| Age (years) | ||||||
| 10 – 12 f | 110 | 8168 ± 3500 | 11 | 6608 ± 5365 | 49 | 7354 ± 3749 |
| 13 – 15 d | 92 | 7181 ± 3454 | 18 | 4746 ± 2632 | 38 | 6732 ± 2837 |
| ≥ 16 d | 102 | 6809 ± 3159 | 20 | 4243 ± 2642 | 40 | 6409 ± 3821 |
| Race/ethnicity % | ||||||
| Non-Hispanic White d | 249 | 7574 ± 3280 | 14 | 5038 ± 2323 | 72 | 7402 ± 3889 |
| African American f | 26 | 5840 ± 3439 | 29 | 4866 ± 4072 | 39 | 5852 ± 2587 |
| Hispanic f | 29 | 7444 ± 4220 | 6 | 5226 ± 2972 | 16 | 6960 ± 3396 |
| SEARCH site | ||||||
| Colorado d | 221 | 7605 ± 3456 | 12 | 4598 ± 2754 | 63 | 7809 ± 3956 |
| South Carolina e | 83 | 6903 ± 3270 | 37 | 5076 ± 3703 | 64 | 5946 ± 2766 |
Type 1: Males > Females, P < .001; 10-12 y > the other 2 groups, P < .05; Non-Hispanic White > African American, P = .01.
Type 2: No differences.
Controls: Males > Females, P < .001; Non-Hispanic White > African American, P = .01.
Type 1 and Controls > Type 2, P < .05.
Type 1 > Type 2, P < .01.
No differences.
Positive correlations were found between steps per day and the physical abilities subscale in the crude analyses (r = 0.29, p < .001; r = 0.31, p = .03; r = 0.31, p < .001) for type 1, type 2, and control youth, respectively (Table 3). After adjustment, correlations remained significant for youth with type 1 diabetes (r = 0.27, p < .001) and controls (r = 0.23, p = .01) but not for youth with type 2 diabetes. For type 2 youth, the correlation was only slightly attenuated but lost statistical significance (r = 0.27, p = .11). This was likely due to reduced power due to the smaller sample size.
Table 3.
Spearman correlations between selected self-concept constructs and pedometer steps per day by case control status (N = 480)
| Type 1 | Type 2 | Controls | |||||||
|---|---|---|---|---|---|---|---|---|---|
| n | r | p | n | r | p | n | r | p | |
| Physical Abilities | |||||||||
| Crude | 304 | 0.29 | <.001 | 49 | 0.31 | .03 | 127 | 0.31 | <.001 |
| Model 1 a | 304 | 0.27 | <.001 | 49 | 0.22 | .14 | 127 | 0.24 | .008 |
| Model 2 b | 299 | 0.27 | <.001 | 45 | 0.27 | .11 | 125 | 0.23 | .01 |
| Physical Appearance | |||||||||
| Crude | 304 | 0.03 | .64 | 49 | 0.25 | .08 | 127 | 0.13 | .16 |
| Model 1 a | 304 | 0.03 | .67 | 49 | 0.25 | .09 | 127 | 0.12 | .20 |
| Model 2 b | 299 | 0.02 | .80 | 45 | 0.46 | .005 | 125 | 0.09 | .36 |
| General Self-Concept | |||||||||
| Crude | 304 | 0.07 | .21 | 49 | 0.17 | .17 | 127 | 0.10 | .27 |
| Model 1 a | 304 | 0.08 | .16 | 49 | 0.18 | .26 | 127 | 0.08 | .39 |
| Model 2 b | 299 | 0.07 | .22 | 45 | 0.28 | .10 | 125 | 0.05 | .59 |
Model 1: adjustment for age, sex, race/ethnicity, site, season.
Model 2: Type 1 and Type 2: adjustment for age, sex, race/ethnicity, site, season, parental education, insulin use, diabetes duration, comorbidities, z-BMI; Controls: adjustment for age, sex, race/ethnicity, site, season, parental education, comorbidities, z-BMI.
There was a significant correlation between steps per day and the physical appearance subscale for youth with type 2 diabetes after the full adjustment (r = 0.46, p = .005). Among youth with type 2 diabetes, higher physical activity was associated with higher perceptions of physical appearance, even after adjustment for z-BMI. There was no association between steps per day and the physical appearance subscale for youth with type 1 diabetes or controls. There was no association between steps per day and general self-concept for youth with type 1 diabetes, type 2 diabetes, or controls.
Discussion
We observed a significant, moderate, and positive correlation between steps per day and the perception of physical abilities. This finding was consistently found among youth with type 1, type 2, and non-diabetic controls. The physical abilities construct of Marsh’s Self-Description Questionnaire assesses the perception of one’s abilities in performing physical activities, sports, and games (17). In a sample of female adolescents, Jackson and Marsh demonstrated that the perceived physical abilities construct was positively associated with self-reported sports participation (11). The physical abilities construct is similar in content to the physical self-concept construct assessed with the Physical Self-Description Questionnaire, also developed later by Marsh (16). Physical self-concept has been shown to be positively associated with self-reported physical activity among adolescent girls, as assessed with the 3-Day Physical Activity Recall (8). Researchers have acknowledged the need for youth to be exposed to different physical activity opportunities to develop skills and increase their confidence and self-efficacy (26,30). Our finding of the positive association between perceived physical abilities and physical activity in youth with either type 1 or type 2 diabetes supports the need for such youth to be exposed to a variety of physical activities, to learn their activity preferences, and to develop skill proficiencies in those activities.
The two other constructs, physical appearance and general self-concept, showed less consistent associations with physical activity compared to perceived physical abilities. First, the physical appearance construct measures one’s perception of his or her attractiveness as compared to others, and the perceptions of how others view him or her (17). A significant, positive correlation of physical appearance with steps per day was found only among youth with type 2 diabetes. Thus, of these youth, those with a higher perception of their physical appearance had higher physical activity levels than their peers with lower perceptions of their physical appearance. After adjustment for z-BMI, the association between physical appearance and steps per day became much stronger. A potential explanation could be that the relation of body image and BMI may differ by race/ethnicity (5,36). Second, general self-concept is defined as the perception of one’s self as an ‘effective, capable individual, proud of and satisfied with the way he or she is’(17). We did not find a significant correlation between physical activity and general self-concept within any of the three groups of youth. This may be due to the broad nature of the general self-concept construct, as recognized by Marsh (17). Parfitt and Eston found a moderate, positive correlation between pedometer-determined steps per day in youth and global self-esteem (r = 0.36) (18). The difference between their findings and ours are most likely due to the differences between the general self-concept and self-esteem constructs.
Our study also provided evidence of limited physical activity in youth with diabetes. We have previously shown that self-reported physical activity falls markedly short of recommended levels (15). Here, we show objective pedometer-based data on steps per day. The physical activity levels of youth in our sample (all 3 groups) were substantially lower (40% to 44%) than American youth in other studies (6,29). Furthermore, youth in our study exhibited activity levels that were 40% to 50% lower than the most recent review for recommended pedometer steps per day (e.g., school-age boys: 13,000-15,000, school-age girls: 11,000-12,000, and adolescent boys and girls: 10,000-11,700) (28). We additionally explored physical activity levels across diabetes type. In the present study, the physical activity level of youth with type 1 diabetes was similar to that of non-diabetic controls, a finding that is comparable to our previous report using the 3-Day Physical Activity Recall (15). However, another study found that physical activity levels of youth with type 1 diabetes were lower than non-diabetic controls (32). With respect to type 2 diabetes, our study found that youth with type 2 diabetes had significantly lower physical activity levels than non-diabetic controls. This is also supported by other research findings. For example, boys with type 2 diabetes had significantly lower levels of moderate-to-vigorous physical activity compared to non-diabetic controls (0.6 ± 0.2 vs. 1.4 ± 0.3 hours per day) (23) and in another study, boys with type 2 diabetes reported fewer 30-minute blocks of vigorous physical activity than non-diabetic controls (1.1 ± 0.4 vs. 2.3 ± 0.3) (15). Thus, the findings from this study indicate an urgent need to increase the physical activity levels of youth with type 1 and type 2 diabetes.
Adherence to medical therapies is important for the successful management of type 1 and type 2 diabetes. High self-efficacy is associated with greater adherence to manage blood glucose levels in adolescents and adults (1,10). Skinner and colleagues found that self-care of diabetes in adolescents and young adults was determined by emotional stability and conscientiousness (25). For children and adolescents with type 1 and type 2 diabetes, glucose control is critical to the reduction of future complications (4,7,24). Regular physical activity is recognized as an important component of the medical therapy for persons with diabetes (3), as physical activity has been shown to improve glucose control and increase insulin sensitivity (12). Our findings demonstrate the need for future studies to examine the effectiveness of interventions to provide different types of physical activities to youth that allow youth to develop their skills. The improvement of their perception of physical abilities may lead to an increase in their physical activity levels. Conversely, low competency for activities may lead to lower perception of physical abilities. Therefore, exposure to different activities may offer youth opportunities to be successful and to learn their preferences for types of physical activity. These findings have particular relevance in this population of children and adolescents who are at high risk for cardiovascular disease.
This study has several important strengths and limitations. Strengths of this study include its large sample of youth with type 1 diabetes, the objective measurement of physical activity, and the valid and reliable measurement of the self-concept constructs. A limitation of this study is its cross-sectional design, which does not allow for the determination of causality. Also, although we had a large sample size, upon stratification, we had a small number of youth with type 2 diabetes (n = 49), which could have contributed to the lack of significant findings in some analyses. However, this sample size reflects the lower prevalence of type 2 diabetes in youth compared to the prevalence of type 1 diabetes in youth (21). There may have been error in the assessment of steps per day, but we do not believe this underestimation would have biased the results. Although the analytic sample consisted of approximately 50% of the SEARCH CC population, the analytic sample was representative of the full SEARCH CC population. Among controls, the only appreciable difference was a greater proportion of excluded youth from Colorado.
In summary, the moderate, positive correlation between physical activity and physical abilities suggests a reciprocal relationship between behavior and perception. Research is needed to investigate whether the provision of opportunities for youth to learn physical activity skills will increase their confidence in being active which in turn may lead to higher physical activity levels. Given the low overall activity levels in youth with diabetes, our findings suggest an urgent need for interventions to target improvement of physical activity levels of youth at high risk for cardiovascular complications.
Acknowledgments:
The SEARCH-CC study was funded by the National Institutes of Health: the National Institute of Diabetes and Digestive and Kidney Disease, R01 DK059184, and the National Institute of Mental Health, R01 MH068126-03. We acknowledge the SEARCH and SEARCH-CC study staff members, as well as the participating patients and their families, for collaboration in the study.
Contributor Information
Jennifer R. O’Neill, Department of Exercise Science, University of South Carolina.
Angela D. Liese, Department of Epidemiology and Biostatistics and Center for Research in Nutrition and Health Disparities, University of South Carolina.
Robert E. McKeown, Department of Epidemiology and Biostatistics, University of South Carolina.
Bo Cai, Department of Epidemiology and Biostatistics, University of South Carolina.
Steven P. Cuffe, Department of Psychiatry, University of Florida College of Medicine-Jacksonville.
Elizabeth J. Mayer-Davis, Departments of Nutrition and Medicine, University of North Carolina at Chapel Hill.
Richard F. Hamman, Department of Epidemiology, University of Colorado.
Dana Dabelea, Department of Epidemiology, University of Colorado.
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