Health-Related Social Disengagement in Elderly ... - Diabetes Care

Epidemiology/Health Services/Psychosocial Research O R I G I N A L

A R T I C L E

Health-Related Social Disengagement in Elderly Diabetic Patients Association with subsequent disability and survival YONG-FANG KUO, PHD1,2 MUKAILA A. RAJI, MD1,3

M. KRISTEN PEEK, PHD1,2 JAMES S. GOODWIN, MD1,2,3

OBJECTIVE — We examined the relationship between health-related social disengagements, as opposed to disengagements related to financial and other non– health-related factors, and subsequent risk of disability and death among initially nondisabled elderly diabetic patients enrolled in Medicare Managed Care plans. RESEARCH DESIGN AND METHODS — We used data from the Medicare Health Outcomes Survey (HOS) Cohort 1 Baseline (1998) and Cohort 1 Follow-Up (2000). Through mail and telephone surveys, trained interviewers collected information on sociodemographic variables, physical and mental health functioning (using Medical Outcomes Study Short Form-36 [SF-36]), activities of daily living (ADL), and medical conditions. This study reported on diabetic subjects aged ⱖ65 years with no ADL disability at baseline (n ⫽ 8,949). Healthrelated social disengagement (degree to which physical health or emotional problems interfere with social activities) was derived from the social functioning subscale of SF-36 (range 0 –100; higher scores depicting better social functioning). RESULTS — For each 10-point increase in social functioning score at baseline, older diabetic subjects in our study experienced an 18% less chance of any ADL disability (odds ratio [OR] 0.82, 95% CI 0.75– 0.89; P ⬍ 0.001) and a 12% less chance of death (0.88, 0.78 –1.00; P ⫽ 0.043) over a 2-year period, adjusting for demographic factors, comorbidities, depression, and general health (assessed by the SF-36). CONCLUSIONS — Among initially nondisabled older diabetic subjects, health-related interferences with social activities at baseline may be early warning signs of subsequent ADL disability and premature death, independent of other measures of health status. Diabetes Care 27:1630 –1637, 2004

T

he disablement process in patients with diabetes involves several steps: progressive accumulation of comorbidities (such as stroke, heart attack, renal failure, and limb amputations), physiologic and anatomic impairments (such as peripheral nerve dysfunction, peripheral artery disease, and visual impairment),

and functional limitations (such as walking limitations and poor balance) (1–11). Research on the disablement process has influenced current research and clinical efforts directed at reducing diabetesrelated disability and mortality. For example, data from the Diabetes Control and Complications Trial (DCCT) Re-

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From the 1Center on Aging, University of Texas Medical Branch, Galveston, Texas; the 2Department of Preventive Medicine and Community Health, University of Texas Medical Branch, Galveston, Texas; and the 3 Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas. Address correspondence and reprint requests to Yong-Fang Kuo, PhD, Sealy Center on Aging, The University of Texas Medical Branch Galveston, TX 77555-0460. E-mail: [email protected]. Received for publication 5 November 2003 and accepted in revised form 26 March 2004. Abbreviations: ADL, activities of daily living; CMS, Center for Medicare and Medicaid Services; COPD, chronic obstructive pulmonary disease; HEDIS, Health Plan Employer Data and Information Set; HOS, Health Outcomes Survey; NCQA, National Committee for Quality Assurance; SF-36, Medical Outcomes Study Short Form-36. A table elsewhere in this issue shows conventional and Syste`me International (SI) units and conversion factors for many substances. © 2004 by the American Diabetes Association.

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search Group and the U.K. Prospective Diabetes Study (UKPDS) Group studies showed that optimal control of blood pressure, blood glucose levels, and lipid levels significantly decreased the risks of diabetic complications and diabetesrelated disability (1,4). However, comorbidities secondary to diabetes do not fully explain the relationship between diabetes and disability (5,6,9). For instance, Gregg et al. (6), in a study of 527 women with diabetes aged ⱖ65 years, reported a 42% increased risk of incident disability (inability to walk, climb stairs, and perform household chores, among others) over a 12-year period, even after adjustments were made for comorbidities (such as stroke and heart disease), visual impairments, functional status, and other potential confounders at baseline. These data suggest that there may be other factors (such as social functioning and health perceptions), in addition to the diabetic-related comorbidities and impairments, which might explain some of the variance in the association between diabetes and disability. In an effort to begin to understand the role of psychosocial factors in individuals with diabetes, a study of 343 patients with type 2 diabetes found that the social impact of diabetes, as well as renal function, diet regimen, age, and smoking history, were more closely associated with mortality than level of diabetes control as measured by HbA1c and other measures of diabetes care (9). Because diabetesrelated pathologies, impairments, and functional limitations do not fully account for the variance in the association between diabetes and disability, it is possible that the effect of physical and emotional health on social engagement may explain some of the variance. Social functioning or social engagement (degree of participation in social activities) has been shown to be associated with disability and mortality (9,12–19). For example, Glass et al. (12) reported, in a group of 2,761 community-dwelling DIABETES CARE, VOLUME 27, NUMBER 7, JULY 2004

Kuo and Associates persons aged ⱖ65 years, that increasing levels of social activities (defined as church attendance; visits to cinema, restaurants, and sporting events; day or overnight trips; participation in social groups; and playing games such as cards or bingo) at baseline were significantly related to decreased mortality during the 13-year follow-up, adjusting for relevant demographic factors and health status. Another study reported significant crosssectional relationships between increased participation in social activities and lower risk of physical disability in a sample of community-residing adults aged ⱖ65 years (19). Degree of participation in social activities depends on several factors, including living arrangement, occupational status, neighborhood composition, physical environment, perception of health benefits, and physical and mental health of the participants (20 –25). Prior studies of determinants of participation in social activities have focused mostly on economic, environmental, and other non– healthrelated factors and how these factors affect disability and survival (17,18,20,23, 24,26). Little is known about how healthrelated limitations on social activities among nondisabled older adults affect future risk of disability and death (27). Specifically, what is the relationship between health-related social disengagements, as opposed to disengagement related to financial and other non– health-related factors, and subsequent risk of disability and death among initially nondisabled elderly diabetic patients? We investigated the association between self-report of health-related curtailment of social activities and risk of disability and death over a 2-year period in a large sample of older diabetic patients enrolled in Medicare Managed Care services. All subjects had no disability in activities of daily living (ADL) at baseline. We chose to use the managed care data to minimize the confounding effect of access to medications and other healthcare services on quality of diabetes care. We hypothesized that, among older diabetic subjects who were initially nonADL disabled, those with better social functioning (lower health-related social disengagement at baseline using Medical Outcomes Study Short Form-36 [SF-36]) would have lower risk of ADL disability and better survival than those with poor social functioning (high health-related soDIABETES CARE, VOLUME 27, NUMBER 7, JULY 2004

cial disengagement) over a 2-year period, adjusting for relevant social demographic factors, general health status (assessed by the SF-36), and comorbidities. RESEARCH DESIGN AND METHODS — Data are from the Medicare Health Outcomes Survey (HOS), a longitudinal cohort mail and telephone survey of Medicare beneficiaries enrolled in Medicare⫹Choice (managed care) plans in the U.S. Medicare HOS was sponsored by Health Care Finance Administration (currently the Center for Medicare and Medicaid Services [CMS]) and developed by National Committee for Quality Assurance (NCQA), a body responsible for accreditation of managed care plans. The Medicare HOS was designed to better evaluate care quality by incorporating key health outcome measures outlined in the Health Plan Employer Data and Information Set (HEDIS) in 1998. Annual participation of Medicare Managed Care Organizations in the HOS has been mandated by CMS since 1998. All Medicare managed plan enrollees, who have been continuously enrolled for at least 6 months, were eligible for sampling, except those who were on Medicare as a result of end-stage renal disease. For baseline survey, in managed care plans with more than 1,000 enrollees, the survey instruments were given to a random sample of 1,000 subjects per plan; in plans with 1,000 enrollees or fewer, the surveys were conducted for all eligible subjects. A full description of the Medicare HOS, rationale, methods, survey design, sample selection, and respondents’ characteristics can be found elsewhere (28 –31). For the 2-year follow-up survey in 2000, subjects were restricted to enrollees participating at baseline survey who were still alive and enrolled in the original managed care plan. We used an analytic data file from the Medicare HOS Cohort 1 Baseline (1998) and the Cohort 1 Follow-Up survey 2 years later. Because many managed care organizations discontinued or consolidated their health plans between 1998 and 2000, the analytic data at the 2-year follow-up comprised 188 managed care markets and 134,076 completed surveys (30). The NCQA-accredited HOS interviewers used standardized questionnaires, survey letters, and follow-up telephone calls (as outlined in the HEDIS

protocol, including a Spanish language version) to collect information on several variables including physical and mental health functioning using SF-36 and ADL impairments using specific symptoms related to various organs, presence of chronic medical conditions, measure of pain, cancer treatment, smoking, and self-rated health and sociodemographic variables. This study reported on diabetic subjects aged ⱖ65 years with no ADL disability at baseline (n ⫽ 8,949). After excluding 155 subjects with incomplete data on baseline social functioning, 8,794 subjects were analyzed for the outcome of death. Due to missing data on social functioning (n ⫽ 53) and ADL (n ⫽ 3), our final sample (n ⫽ 5,232) for the ADL analysis comprised those subjects who completed the 2-year follow-up interviews and who had complete data on baseline social functioning and follow-up ADL. Causes of nonparticipation at the 2-year follow-up surveys were disenrollment (n ⫽ 2,443), death (n ⫽ 471), and refusal or inability to contact (n ⫽ 700). Fortyseven subjects with no available data were coded in the Analytic Database as “invalid.” The characteristics between the subjects who completed the 2-year follow-up and the subjects who dropped out from follow-up were compared. There was no significant difference in social functioning scores between the two groups. However, the higher dropout rates were found among nonwhites, subjects with depression, and subjects with cancers and chronic obstructive pulmonary disease (COPD). Diagnosis of diabetes and other comorbidities were by self-report. We used information on relevant sociodemographic variables, chronic medical conditions, social functioning component of SF-36 and other variables at baseline, and data on ADL and mortality at the 2-year follow-up interview (2000), as contained in the Cohort 1 Analytic Public Use File published by CMS, Health Services Advisory Group, in January 2003 (30). SF-36 Health Survey The SF-36 is a 36-item measurement instrument used to assess health status and health-related quality of life (32,33). The SF-36 survey instrument (the whole instrument or its subscales) is among the most frequently used health status measures in studies of older adults (31–35). It 1631

Social disengagement, disability, and death

has two summary scales, the Physical Component Summary and the Mental Component Summary, which were derived from eight subscales: physical functioning, role-physical, bodily pain, general health, vitality, social functioning, role-emotional, and mental health. Social functioning subscale. The social functioning subscale (range 0 –100) was derived from responses to two questions such as, “During the past 4 weeks, to what extent has your physical health or emotional problems interfered with your normal social activities?” (responses range from not at all to slightly, moderately, quite a bit, and extremely) and “During the past 4 weeks, how much of the time has your physical health or emotional problems interfered with your social activities?” (responses range from all, most, some, a little, to none of the time). Lower scores on any or all of the scales indicate poorer health functioning. Standardized scores on SF-36 for the U.S. population are used in most studies to calculate a normalized score. A score of 50 represents the national average for the summary scores and for the subscales. A score that is 10 points above or below the mean score of 50 represents a difference of 1 SD from the national average. ADL scale. There were six ADL questions in the Medicare HOS. These included walking, bathing, dressing, eating, getting in or out of chairs, and using the toilet. Respondents were asked to indicate whether they could perform these activities without help, if they needed help, or if they were unable to do them. “No disability” was defined as needing no help, and “any disability” was defined as needing help with or unable to perform one or more of the six ADL. Death. The indicator of decease (without the specific date of death) at the 2-year follow-up interview (2000) was from the Cohort 1 Analytic Public Use File published by CMS, Health Services Advisory Group, in January 2003 (30). Covariates Factors potentially associated with disability and mortality among individuals with diabetes include sociodemographic variables (age, sex, ethnicity, marital status, years of formal education, smoking status), comorbidities (hypertension, angina or coronary artery disease, myocardial infarction, stroke, COPD, arthritis, cancer), and history of depressive symp1632

tomatology, assessed by a positive screen on a depression questionnaire (36). Positive depression screen was assessed by an affirmative answer to any of the following questions: 1) “In the past year, have you had 2 weeks or more during which you felt sad, blue, or depressed, or when you lost interest or pleasure in things that you usually cared about or enjoyed?”; 2) “In the past year, have you felt depressed or sad much of the time?”; 3) “Have you ever had 2 years or more in your life when you felt depressed or sad most days, even if you felt okay sometimes?” Statistical analysis We examined demographic and health factors for diabetic subjects, stratified by ADL disability and death at 2-year followup, using descriptive and t tests for continuous variables and contingency tables (␹2) for categorical variables. Two logistic regression models were used to predict the risk of ADL disability and death. The first model is unadjusted; the second model added covariates that were significantly associated with ADL limitation or death in the bivariate analyses, i.e., age, sex, marital status, smoking status, depression, comorbidities, and general health from SF-36. All analyses were estimated using the SAS System for Windows, version 8.2 (SAS Institute, Cary, NC). RESULTS — Descriptive demographic and health factors for initially nondisabled older diabetic subjects, stratified by incident ADL disability and death at 2-year follow-up, are shown in Table 1. Significant bivariate correlates of ADL disability and death among older diabetic subjects included older age, being unmarried, depression, history of myocardial infarction and other heart condition, stroke, COPD, arthritis of hip or knee, cancer, and increasing number of comorbidities. Ethnicity was not significantly associated with ADL disability or mortality. The difference in baseline social functioning scores according to ADL disability and death were also analyzed (data not shown). Baseline social functioning scores were significantly lower among the disabled and the deceased (mean ⫾ SD, 49.9 ⫾ 9.5 vs. 52.9 ⫾ 7.5 for disabled and nondisabled, P ⬍ 0.001, and 49.0 ⫾ 10.5 vs. 51.8 ⫾ 8.5 for deceased and alive, respectively, P ⬍ 0.001). Table 2 shows, in the unadjusted

model (model 1), a significant association between higher scores on social functioning measures (as a continuous variable) and increased risk of ADL disability at the 2-year follow-up (P ⬍ 0.001). After full adjustments were made for age, sex, marital status, smoking, myocardial infarction and other heart conditions, stroke, COPD, arthritis, cancer, depression, and general health of the SF-36 (model 2), increasing social functioning scores were still predictive of lower odds of ADL disability at the 2-year follow-up. For each 10-point increase in social functioning score at baseline, older diabetic subjects in our study experienced 18% lower risk of any ADL disability (odds ratio [OR] 0.82, 95% CI 0.75– 0.89; P ⬍ 0.001). The results of two logistic regression analyses predicting the risk of death are also shown in Table 2. In model 1, increasing scores on social functioning measures at baseline were significantly associated with decreased odds of death (P ⬍ 0.001). With full adjustment for age, sex, marital status, education, depression, comorbidities, and general health (model 2), better social functioning at baseline was associated with decreased risk of 2-year mortality. For each 10-point increase in social functioning score at baseline, older diabetic subjects in our study experienced 12% lower risk of death (OR 0.88, 95% CI 0.78 –1.00; P ⫽ 0.043) over a 2-year period. CONCLUSIONS — Our findings can be summarized as follows: among community-dwelling initially nondisabled diabetic subjects aged ⱖ65 years in the Medicare Managed Care program, higher scores for measures of social functioning (less health-related social disengagement) at baseline were significantly associated with better survival and less ADL disability over a period of 2 years, controlling for age, sex, marital status, depression, general health, and comorbidities. There was a stepwise decrease in the risk of future ADL disability and death with better scores on social functioning at baseline, such that with each 10-point increase in social functioning score (less healthrelated social disengagement), older diabetic subjects in our study experienced 18% lower risk of any ADL disability and 12% lower risk of death over 2 years of follow-up. Prior research has reported on associations between lower level of social activDIABETES CARE, VOLUME 27, NUMBER 7, JULY 2004

Kuo and Associates

Table 1—Characteristics of mortality and incident ADL disability among older diabetic patients without any ADL disability at baseline

Characteristic

Number of subjects at baseline

Death at 2 years follow-up (%)*

Number of subjects at follow-up†

ADL disability at follow-up (%)*

8,949

5.3

5,235

29.2

6,080 2,869

4.0 8.0

3,617 1,618

25.7 37.2

4,195 4,627

4.1 6.3

2,489 2,684

31.5 27.0

7,161 903 618

5.1 6.1 4.9

4,271 491 330

28.8 32.6 27.3

2,882 2,899 2,946

5.6 5.5 4.5

1,672 1,745 1,715

34.2 27.5 26.0

5,682 3,143

4.5 6.4

3,392 1,784

28.1 31.3

3,636 713 4,032

4.3 5.9 5.6

2,182 424 2,341

29.1 32.1 28.5

1,915 6,894

6.3 4.9

1,044 4,121

38.2 26.9

5,850 3,048

5.4 4.9

3,399 1,810

30.9 26.1

1,665 7,128

5.9 5.0

948 4,204

36.1 27.5

1,142 7,263

9.5 4.6

638 4,497

37.2 28.0

1,761 7,058

7.2 4.8

1,015 4,151

36.9 27.1

601 8,244

7.7 5.0

317 4,869

39.1 28.4

750 8,091

7.9 5.0

400 4,780

40.3 28.1

2,455 6,400

4.4 5.6

1,434 3,745

39.8 25.2

2,460 6,390

4.6 5.5

1,422 3,761

35.5 26.8

1,085 7,784

9.1 4.6

637 4,557

35.2 28.4

1,169 2,666 2,262 2,356 496

4.1 4.5 5.1 6.1 9.1

687 1,575 1,350 1,364 259

18.6 23.3 30.4 35.6 53.7

Total Age (years) 65–74 ⱖ75 Sex Women Men Ethnicity White Black Other Education (completed grade) ⬍9 9–12 ⬎12 Marital status Married Unmarried Smoking status Never smoker Current smoker Former smoker Depression Yes No Comorbidities Hypertension Yes No Angina or coronary artery disease Yes No Myocardial infarction Yes No Other heart condition Yes No Stroke Yes No COPD Yes No Arthritis of hip or knee Yes No Arthritis of hand or wrist Yes No Cancer Yes No Number of comorbidities None 1 2 3–4 ⱖ5

Data are n or %. *Percentages in bold indicate significant group differences at P ⱕ 0.05. †Of 5,288 subjects who completed 2-year follow-up, 53 subjects had missing data on ADL measurement.

DIABETES CARE, VOLUME 27, NUMBER 7, JULY 2004

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0.66

(0.62–0.71)

95% CI 0.73

(0.67–0.80)

95% CI

⬍0.001

P

0.88 0.53 2.04 0.61

OR

0.319

0.018 0.021 0.014 0.008 ⬍0.001 0.011 0.065 ⬍0.01

(0.94–1.55) (0.88–1.18)

(1.04–1.55) (1.03–1.44) (1.07–1.84) (1.09–1.76) (1.60–2.13) (1.06–1.56) (0.99–1.40) (0.67–0.80)

† † 1.10 0.65 2.12 1.19 1.36 1.50 0.78 0.91 2.00 0.97 0.74

⬍0.001 ⬍0.001 0.058 0.430

OR

1.21 1.02 † † 1.27 1.22 1.40 1.38 1.85 † 1.29 1.18 0.73

(0.75–0.89) (0.51 ⫾ 0.68) (0.75–1.01) (0.91–1.24)

P

1.15 1.26

0.82 0.59 0.87 1.06

⬍0.001

95% CI

Model 1

† †

OR

P

Model 2

Death

(0.88–1.37) (0.48–0.89) (1.58–2.84) (0.92–1.52) (0.96–1.93) (1.09–2.05) (0.60–1.01) (0.70–1.18) (1.55–2.57) (0.74–1.26) (0.65–0.84)

(0.88–1.50) (0.97–1.65)

(0.78–1.00) (0.43–0.65) (1.61–2.58) (0.49–0.76)

95% CI

Model 2

0.402 0.004 ⬍0.001 0.185 0.086 0.012 0.062 0.560 ⬍0.001 0.801 ⬍0.001

0.101

0.043 ⬍0.001 ⬍0.001 ⬍0.001

P

*Item derived from SF-36 — continuous scores in 10-point increase used for analyses; higher scores depict better function/health. †Variable was not significantly associated with outcome in bivariate analysis and was not included in the multivariate models.

Social functioning (0–100)* Age (65–74 vs. ⱖ75 years) Sex (men vs. women) Marital status (married vs. unmarried) Education (grades completed) ⬍12 vs. ⬎12 9–12 vs. ⬎12 Smoking Current vs. never Former vs. never Hypertension (yes vs. no) Angina or coronary artery disease (yes vs. no) Myocardial infarction (yes vs. no) Other heart condition (yes vs. no) Stroke (yes vs. no) COPD (yes vs. no) Arthritis of hip or knee (yes vs. no) Arthritis of hand or wrist (yes vs. no) Cancer (yes vs. no) Depression (yes vs. no) General health (0–100)*

OR

Model 1

ADL disability

Table 2—Multivariate logistic regression models assessing the independent relationship between social functioning scores at baseline and ADL disability and death 2 years later, adjusting for relevant risk factors, among older adults living with diabetes



Kuo and Associates

ities and increased risk of disability and mortality (9,12,14 –16,18,19,37). For example, data from the New Haven Established Populations for Epidemiologic Study of the Elderly showed that increased participation in social activities (such as visits to theaters, game playing, shopping, and church attendance, among others) was associated with lower risk of physical disability (19). Similarly, Lennartsson et al. (16), using data from the Swedish Panel Study of Living Conditions of the Oldest Old, showed that increased participation in social activities was associated with reduced risk of death at 4-year follow-up, adjusting for health variables and other relevant confounders. Our results extend these studies to older initially nondisabled individuals with diabetes across the U.S. by showing that healthrelated social disengagements are associated with higher risk of subsequent disability and death, adjusting for relevant confounders. In other words, among elderly diabetic subjects with no selfreported ADL disability, a decrease in social activities might be a forerunner of subsequent loss of independent living and premature death. The mechanism for the association of participation in social activities with lower disability and mortality is not clear. Past studies suggested that engagement in social activities might be associated with several factors, including an optimal sense of self-competence and selfefficacy, slower cognitive decline, and an improved blood markers of immune and stress response, factors known to improve the odds for disability-free survival (38 – 41). Our study included no data on measures of self-efficacy, blood markers, and other factors to explore these factors as possible mediators for the link between health-related social disengagement and our outcome measures. On the other hand, it is possible that decreasing participation in social activities by nondisabled individuals with diabetes is a marker for severity of comorbidity, not just mere presence of a disease. Therefore, an unrecognized medical condition (i.e., subclinical stroke or subclinical depression) might be causing a decrease in both the ability (and the motivation) to engage in social activities and the ability to perform ADL. In that scenario, the decrease in social activities is captured much earlier by assessing patients’ responses to social functioning DIABETES CARE, VOLUME 27, NUMBER 7, JULY 2004

questions during a period when the subjects reported no ADL disability. However, over a 2-year follow-up period, with progressive decrease in level of social activities (with potential loss of the known health benefits of participation in social activities) as well as the persistence of the unrecognized condition, deficits in ADL performance accumulate, leading to physical disability, loss of independence, and death. We have no direct evidence in our study that incident ADL disability (and death) at follow-up is due to stroke or any specific medical condition that can potentially lead to decrease in participation in social activities and ADL ability. Due to lack of data in our study on severity of diabetes (such as HbA1c level), we are not able to determine whether healthrelated interference with social activities is a marker for poor diabetes control among older diabetic patients with no self-reported ADL disability. Our findings seem to indicate that even when no ADL disability is clinically evident, patients start, perhaps at an early presymptomatic stage of disablement, to adjust their levels of social activities in response to their perceptions of physical and emotional disturbances. Therefore, inquiry about status of social activities in older diabetic subjects by clinicians is one way to identify individuals who will benefit most from interventions to stem the future loss of independence. This study has some limitations. First, the diagnosis of diabetes and comorbidities were by self-report. However, prior research showed good agreement between self-reported diabetes and diabetes diagnosed by blood tests (42,43). Nonetheless, it is conceivable that subjects might under-report comorbidities (such as peripheral artery disease and peripheral neuropathy), partly because of underdiagnosis and misattribution to aging. It is also possible that, due to diabetesrelated nerve damage, the prevalence of self-reported angina could be underestimated. Second, we did not include data on adherence to medication and duration of diabetes, factors known to impact diabetes-related morbidity and mortality (1– 4). Medicare managed plan enrollees receive coverage for drugs, and this improved access should minimize the impact of differences in medication availability on our outcomes. Third, the Medicare HOS database has no detailed information on types and frequency of so-

cial activities. Fourth, the results of the association between health-related social disengagement and ADL disability might only be generalized to the diabetes population without severe chronic comorbidities of cancer and COPD, among others. Another limitation of our study is our use of unweighted analyses, which do not account for potential intraclass correlation within health plans. However, to explore potential effects of selection and nonresponse, Hwang et al. (44), using a weighted scheme to adjust for selection and nonrespondent bias in Medicare HOS data, found similar estimates of physical and mental functions on SF-36 between the weighted and unweighted analyses. Nonetheless, the standard errors of estimates were higher in the weighted analyses. Because the dummy identifier of health plans and the weighting schemes were not available in the Cohort 1 Analytic Public Use File, we were not able to perform weighted analysis. Despite these limitations, our source of data has several strengths, including its large sample and its nationwide spread of older enrollees in managed care plans across the U.S. In conclusion, our study found that health-related limitations of social functioning are significantly predictive of ADL disability and death over a period of 2 years among initially nondisabled older diabetic Americans enrolled in Medicare managed care plans. Multiple approaches are needed to maintain independent living and better survival in elderly diabetic individuals. Older diabetic subjects who report curtailing their social activities might be at high risk of subsequent disability and, as such, should be targeted for more rigorous evaluation and management of any modifiable underlying emotional or physical disorders. Improving disability-free survival in older patients with diabetes requires a better understanding of social functioning and social support in this population. Given the fact that the population aged ⱖ65 years is one of the fastest growing segments in the U.S., the current findings have important implications for health care planning and resource allocation to maintain independence in older adults living with diabetes.

Acknowledgment — This study was supported by Agency for Health Research and Quality Grant HS-11618. M.A.R. is supported

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