Factors contributing to higher incidence of diabetes for black Americans

Diabetes is a disease that occurs when your blood glucose (also called blood sugar) is too high. Blood glucose is the body’s main source of energy. Insulin, a hormone made by the pancreas, helps glucose get into your cells to be used for energy. In type 2 diabetes, your body doesn’t make enough insulin or doesn’t use insulin well. Too much glucose then stays in your blood, and not enough reaches your cells. Over time, too much glucose in your blood can cause health problems, such as heart disease, nerve damage, eye problems, and kidney disease.

You can develop type 2 diabetes at any age. However, type 2 diabetes occurs most often in middle-aged and older people. You’re more likely to develop type 2 diabetes if you are 45 or older, have a family history of diabetes, or are overweight or obese. In the U.S., black adults are nearly twice as likely as white adults to develop type 2 diabetes. This racial disparity has been rising over the last 30 years.

To investigate potential causes for this health disparity, a team led by Dr. Mercedes R. Carnethon at Northwestern University Feinberg School of Medicine analyzed data collected from more than 4,200 participants in the CARDIA (Coronary Artery Risk Development in Young Adults) study. The research was supported in part by NIH’s National Heart, Lung, and Blood Institute (NHLBI). Results were published in JAMA on December 26, 2017.

Study participants were recruited at ages 18 to 30 years from Birmingham, Alabama; Chicago, Illinois; Minneapolis, Minnesota; and Oakland, California. About 49% of participants were black; 54% were women. The researchers collected information from participants about different risk factors for diabetes over 30 years. They gathered personal and family medical history, as well as information about participants’ weight and health habits like smoking, drinking, and diet. They also tracked information about participants’ neighborhoods, education level, ability to pay bills, and employment status throughout young adulthood.

The study found that the chance of developed diabetes was significantly higher for black adults than for white adults (about 66 more cases of diabetes per 1,000 people). The greatest difference was between black women and white women.

The researchers used statistical analyses to determine how biological, neighborhood, psychosocial, socioeconomic, and behavioral risk factors contributed to rates of diabetes. They found that biological risk factors accounted for most of the health disparity. These factors included a combination of body mass index, waist measurement, fasting glucose levels, lipids, blood pressure, and lung function. Differences between blacks and whites in neighborhood, psychosocial, socioeconomic, and behavioral factors were also linked with diabetes, although to a lesser degree.

“Obesity is driving these differences,” Carnethon says. “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…. 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.”

—by Tianna Hicklin, Ph.D.