Modifiable Factors May Explain Higher Risk of Diabetes in Blacks

Marlene Busko

December 29, 2017

Modifiable biologic, neighborhood, psychosocial, socioeconomic, and behavioral risk factors may explain most of the approximately two-fold higher risk of developing type 2 diabetes in blacks vs whites, researchers report.

The study, which included more than 4000 participants in the Coronary Artery Risk Development in Young Adults (CARDIA) study in their mid-20s who were followed into middle age, was published in the December 26 issue of the Journal of the American Medical Association.

"These results suggest prevention efforts that address racial inequalities in socioeconomic factors (eg, educational attainment and income) may be one strategy to reduce racial disparities in diabetes risk," Michael P Bancks, PhD, from Northwestern University in Chicago, Illinois, and colleagues report.

Previous studies suggest that living in a disadvantaged neighborhood, inadequate access to healthcare, and having a low education level can lead to poor health-related behaviors and contribute to worsening biological factors, the researchers note.

"Findings from the present study support this hypothesis as individual-level and neighborhood-level social determinants did contribute significantly to disparities in diabetes."

Racial Differences in Risk Factors for Diabetes

In the past decade, the greatest increase in the onset of diabetes has been in young blacks, Dr Bancks and colleagues note.

Using data from CARDIA, they aimed to investigate how modifiable diabetes risk factors during young adulthood might explain racial differences in the incidence of type 2 diabetes in middle age.

"The diabetes risk factors that were selected were modifiable, available in the study, known to vary by race in the literature, and categorized into the following groups: biological, neighborhood, psychosocial, socioeconomic, and behavioral," the researchers explain.

They identified 4251 participants in CARDIA who were 18 to 30 years old when they entered the study in four American cities in 1985 to 1986 and had complete data through 2015 to 2016.

At baseline, participants were a mean age of 25 years, half (49%) were black, and 54% were women.

On average, blacks had worse socioeconomic status; they were less likely to have completed high school, work, be married, or have parents who completed high school.

In addition, blacks were more likely to report that their household had difficulty paying for essentials and were more likely than whites to live in a poor neighborhood.

They were also more likely to have certain poor health behaviors; they were more likely to be current smokers (32% vs 26%), and black women were less likely to be at least moderately physically active. 

Racial differences in biological variables included a higher mean body mass index and mean systolic blood pressure in blacks compared with whites.

During a mean follow-up of 25 years, 315 blacks and 189 whites developed type 2 diabetes.

After adjusting for age and study location, black women were nearly three-times more likely to develop diabetes than white women (hazard ratio [HR], 2.86; 95% CI, 2.19 – 3.72).

Similarly, black men were more likely to develop diabetes than white men (HR, 1.67; 95% CI, 1.28 – 2.17).

However, in models that successively adjusted for age and location, then biological, neighborhood, psychosocial, socioeconomic, and behavioral factors, there were no significant racial differences in the incidence of diabetes.

Specifically, in the model adjusted for all variables, black women were not significantly more likely to develop diabetes than white women (HR, 0.79; 95% CI, 0.55 – 1.14). Similarly, black men were not more likely to develop diabetes than white men (HR, 0.92; 95% CI, 0.62 – 1.38).

Thus, "differences in traditional modifiable diabetes risk factors between black and white individuals may contribute to the racial disparity in diabetes incidence in middle age," the authors summarize.

CARDIA is supported by the National Heart, Lung, and Blood Institute (NHLBI), University of Alabama at Birmingham, Northwestern University, University of Minnesota, Kaiser Foundation Research Institute, Johns Hopkins University School of Medicine, and Intramural Research Program of the National Institute on Aging. Dr Bancks received support from the NHLBI for the current study.

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JAMA 2017;318:2457-2465. Abstract

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