Association of Socioeconomic Status with Mortality in Type 1 Diabetes: The Pittsburgh Epidemiology of Diabetes Complications Study

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Purpose

Socioeconomic status (SES) as a risk factor for mortality in type 1 diabetes (T1D) has not been adequately studied prospectively.

Methods

Complete clinical and SES (income, education, occupation) data were available for 317 T1D participants in the Pittsburgh Epidemiology of Diabetes Complications Study within 4 years of age 28 (chosen to maximize income, education, and occupational potential, and to minimize the SES effect of advanced diabetes complications). Vital status was determined as of 1/1/2008.

Results

Over a median 16 years of follow-up, 34 (10.7%) deaths occurred (standardized mortality ratios [SMRs] = 4.1, 95% confidence interval [CI]: 2.7–5.5). SMRs did not differ from the general population for those in the highest education and income groups, whereas in those with low SES, SMRs were increased. Mortality rates were three times lower for individuals with a college degree versus without a college degree (p = 0.004) and nearly four times lower for the highest income versus lower income groups (p = 0.04). In Cox models adjusting for diabetes duration and sex, education was the only SES measure predictive of mortality (hazard ratio [HR] = 3.0, 95% CI: 1.2–7.8), but lost significance after adjusting for HbA1c, non-HDL cholesterol, hypertension, and microalbuminuria (HR = 2.1, 95% CI: 0.8–5.6).

Conclusions

The strong association of education with mortality in T1D is partially mediated by better glycemic, lipid, and blood pressure control.

Introduction

Mortality is inversely associated with socioeconomic gradients in the general population 1, 2, 3, 4. Disadvantaged individuals have higher rates of mortality, and data suggest this inequality is becoming more apparent over time (5). However, only a few studies have examined the relationship between socioeconomic status (SES) and mortality in diabetes, specifically type 1 diabetes, and study designs and definitions of SES measures have varied widely.

Some studies report a clear SES gradient in mortality for those with diabetes 6, 7, 8, whereas others have reported that SES plays less of a role or no role in mortality in those with diabetes compared to the general population 9, 10, 11. The SES differences in mortality seen for individuals with diabetes seems to be largely the result of cardiovascular-related deaths. A disproportionate number of these cardiovascular deaths have occurred among individuals with type 1 diabetes 7, 10. Noted associations between SES and mortality in the literature differ by SES measures, and studies separating diabetes by type report a stronger association of SES with type 1 diabetes 7, 8.

Given these diverse data in the literature, we examined the relationship between SES and all-cause mortality using a large prospective cohort of childhood-onset type 1 diabetes. Three different SES measures were captured at or near age 28, including household income, education, and occupation, and were used to evaluate this relationship. We also sought to identify which SES measures were most strongly associated with all-cause mortality in type 1 diabetes.

Section snippets

Study Population

Participants in the Pittsburgh Epidemiology of Diabetes Complications (EDC) Study, an ongoing prospective investigation of patients with childhood-onset (age = <17 years) type 1 diabetes were included in this analysis. EDC participants (n = 658) were either diagnosed or seen within 1 year of diagnosis at Children’s Hospital of Pittsburgh between 1950 and 1980 and were on insulin therapy at initial discharge. Participants have been followed biennially by survey since the baseline examination in

Results

Over a median follow-up time of 16.3 years (range: 2.0–21.7 years), there were 34 (10.7%) deaths in our Age 28 cohort of childhood-onset type 1 diabetes as of January 1, 2008. No differences by sex, age, race, or diabetes duration were seen at the Age 28 baseline examination (Table 1). Of the SES measures, income and education level were associated with mortality in type 1 diabetes; occupation was not. The highest income group comprised 20.1% of the surviving cohort, but only 5.9% of deaths (p

Discussion

These data indicate that all-cause mortality rates in type 1 diabetes are significantly associated with education and income levels attained by early adulthood. Low income and low education groups had significantly higher rates of all-cause mortality compared to the local general population, whereas high income and education groups did not significantly differ from the general population in their mortality rates. Cox proportional hazards modelling revealed that education and income were

Acknowledgments

This work was supported by the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health (R01-DK034818 and F30-DK082137 to A.M.S.).

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