In a surprising finding, blacks and whites have the same
risk of developing diabetes when all biological factors for the disease are
considered over time, reports a large  study published in JAMA.  

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.

“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.”

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.

But this study, for the first time, 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. 

Before the authors accounted for the differences in risk
factors, black women had nearly three times the risk for developing diabetes as
white women.

“Blacks gained more weight over time,” Carnethon said. “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. But 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 behaviors 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 findings are particularly important because the
incidence of diabetes is rising in black youth ages 10 to 19 years old. There
is no easy fix for the problem, which is driven by a combination of biological,
neighbourhood, psychosocial, socioeconomic and behavioural factors, the authors

“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. 

Changing risk behaviours in childhood and adolescence is key
because that’s when risky health behaviors develop and damage begins to
accumulate, Bancks said.

The research is part of the observational cohort Coronary
Artery Risk Development in Young Adults (CARDIA) Study. CARDIA was started in
1985-1986, enrolling 5115 black and white men and women who were 18 to 30 years
of age from Birmingham, Alabama; Oakland, California; Minneapolis and Chicago.

The Northwestern study sample included 4251 individuals from
the original study. Individuals were followed through 2015 to 2016 for the development
of diabetes, which was assessed at eight follow-up examinations over these 30
years using standard diagnostic criteria for diabetes. 

“If we could wave a magic wand and get rid of risk
factors, then we could eliminate the disparity,” Carnethon said. “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.”