January 29, 2018
After an average 4.5-year follow-up, 12% of blacks and 6% of whites developed type 2 diabetes.
Among those with morbid obesity (BMI > 40 kg/m2), however, 20% of blacks and 17% of whites developed diabetes during this short follow-up.
The findings were published online January 11 in PLoS One by Baqiyyah N Conway, PhD, from the University of Texas Health Science Center, in Tyler, and colleagues.
"The study reveals that rates of diabetes are exceptionally high among low-income southerners who are morbidly obese," senior author William J Blot, PhD, research professor of medicine at Vanderbilt University Medical Center, in Nashville, Tennessee, told Medscape Medical News in an email.
It also shows that "among adults of normal weight, diabetes was more than twice as common among blacks than whites ... but as BMI rose to levels over 40 kg/m2 the [excess incidence of diabetes in blacks] nearly disappeared," indicating that obesity has a greater impact on risk of diabetes in whites.
The researchers estimate that within 20 years, among the morbidly obese individuals in this cohort, three quarters of men and two thirds of women — of both races — will have developed diabetes.
And "these high percentages were estimated using a conservative definition of diabetes, requiring use of medications to treat the condition," Dr Blot noted in a statement.
"Our striking findings suggest that the SCCS cohort may be a harbinger signaling further increases to come in other American populations where obesity is common."
Clues Gleaned From 12 Southern States, With 44% Obesity Rate
Surveys by the US Centers for Disease Control and Prevention show that in the obesity belt the prevalence of obesity (BMI ≥ 30 kg/m2) has increased from 10–14% in 1990 to over 30% in 2010.
Obesity is a major risk factor for type 2 diabetes and is also more common among blacks than whites, and people with low incomes or low education levels compared with those of higher socioeconomic status.
Researchers aimed to examine new-onset diabetes among blacks and whites in the SCCS to provide "clues to what may befall other American populations affected by the obesity epidemic."
Participants were from 12 states in the obesity belt (Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Virginia, and West Virginia) and mainly recruited from community health centers in underserved areas.
SCCS enrolled 85 000 adults who were 40 to 79 years old during 2002 to 2009. Two-thirds were black and about 20% had diabetes.
The current analysis consisted of 24 000 blacks and 14 064 whites who did not have diabetes at baseline and completed the first follow-up survey around 4.5 years after enrollment.
Among participants with a normal weight (BMI 20 to 25 kg/m2), incident diabetes was more than twice as common among blacks than whites (6% vs < 2%, respectively).
Racial Divide in Diabetes Disappears With Increasing BMI
However, with increasing BMI, rates of new diabetes increased among both blacks and whites, and the racial gap decreased.
The reasons for the higher rates of diabetes among blacks than whites of normal weight are not fully known, but likely involve a genetic component, said Dr Blot, as the difference persisted after adjusting for socioeconomic status, diet, and physical activity.
Individuals diagnosed with diabetes were more likely to have a low education level and a lower household income, and they were less likely to have private insurance.
The link between a lack of a high school diploma and risk of diabetes was greater in whites.
The impact of obesity on risk of diabetes was also larger in whites.
For example, among blacks, compared to those with a normal BMI (20 to 25 kg/m2), those with morbid obesity (BMI ≥ 40 kg/m2) were four times more likely to have incident type 2 diabetes during the average 4.5-year follow-up — after adjusting for all confounding factors.
Among whites, however, compared to those with a normal BMI, those with morbid obesity were 12 times more likely to have incident type 2 diabetes, after adjusting for these same variables.
Findings showed a similar pattern in the patients who completed a second follow-up survey a median 3 years after the first survey.
"We know that obesity is a prime risk factor for the development of type 2 diabetes among adults," stressed Dr Blot.
"But this study shows that its impact was even greater than expected and reinforces the need to address obesity, especially among poor patients, to avoid even more cases of diabetes which can be debilitating, deadly, and costly," he concluded.
The study was supported by grants from the National Institutes of Health, National Cancer Institute, and National Institute of Diabetes and Digestive and Kidney Diseases. The authors have reported no relevant financial relationships.