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Race and T2DM

Race plays no role in early onset risk of T2DM, obesity does

The finding flips long-held beliefs that there is an unexplained or genetic reason why blacks have double the rate of diabetes compared to whites by midlife, which is considered early onset

Previous studies have found higher rates of diabetes in blacks are still present even when risk factors for diabetes such as obesity and lower socioeconomic status are taken into account however, a recent study by researchers at Northwestern University Feinberg School of Medicine has identified a combination of modifiable risk factors over time - body mass index, fat around the abdomen, fasting glucose levels, lipids, blood pressure and lung function - that drive the higher rate of diabetes. When all of these were factored out, there were no disparities between black and white men or women.

"Obesity is driving these differences," said senior study author, Mercedes Carnethon, associate professor of preventive medicine at Northwestern University Feinberg School of Medicine. "The findings surprised us, because for the past 20 years there was a narrative that there must be something we haven't found that was causing this higher rate. Blacks gained more weight over time, it was the accumulation of this and other risk factors that eliminated the so-called mysterious cause of the disparity."

In previous studies, researchers measured such health behaviours as obesity, physical activity and diet once during their study participants' lives. However, these factors can change over time, and how much they change may be different in each race group. For example, a white woman and a black woman may be the same weight at age 35 - but if that black woman gains more weight over the next 15 years, her risk for developing diabetes goes up.

The Northwestern study measured these changes in her weight over time, along with changes in other related health behaviours and health risk factors. When scientists accounted for these changes in risk factors for diabetes, they did not observe race differences in the development of diabetes.

The study, ‘Association of Modifiable Risk Factors in Young Adulthood With Racial Disparity in Incident Type 2 Diabetes During Middle Adulthood’, published in JAMA, included black and white men and women from the observational Coronary Artery Risk Development in Young Adults study, aged 18 to 30 years, without diabetes at baseline (n=4,251) who were followed from 1985-1986 to 2015-2016.

IN total, 49% (n=2,066) of the sample was black and 54% (n=2,304) were women. Over a mean follow-up of 24.5 years, 504 cases of incident diabetes were identified. Using sex-stratified multivariable-adjusted Cox proportional hazards models, black women and men were more likely to develop diabetes than white men and women. Biological factors were most strongly associated with the disparity in diabetes risk between black and white individuals for women and men. There was no longer disparity in diabetes risk between black and white middle-aged adults after adjustment for biological, neighbourhood, psychosocial, socioeconomic and behavioural factors measured over time.

"To eliminate the higher rate of diabetes, everybody needs to have access to healthy foods, safe spaces for physical activity and equal economic opportunity to have enough money to afford these things and live in communities that offer this," said lead study author, Michael Bancks, a postdoctoral fellow in preventive medicine at Feinberg.

"If we could wave a magic wand and get rid of risk factors, then we could eliminate the disparity," added Carnethon. "But we can't do that. Still, we now know there is no mystery to these higher rates. Our efforts to control the traditional risk factors can work to reduce the disparities we observe in diabetes incidence."

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