People who are obese and have low levels of vitamin D have a higher risk of developing insulin resistance (when insulin becomes less effective at lowering blood sugar) than those who have just one of those two risk factors.
"Stay active to help prevent diabetes."
Both obesity and low vitamin D are associated with a greater risk of diabetes.
Longjian Liu, MD, PhD, of Drexel University School of Public Health, and colleagues found that the combination of obesity and low vitamin D increases the risk of insulin resistance more than they had predicted.
According to their results, obese people with healthy vitamin D levels were nearly 20 times more likely to have insulin resistance than total study population.
Obese people who also had low levels of vitamin D were about 32 times more likely to have insulin resistance.
"Vitamin D insufficiency and obesity are individual risk factors for insulin resistance and diabetes," said Shaum Kabadi, MPH, a doctoral candidate at Drexel University and lead author of the study.
"Our results suggest that the combination of these two factors increases the odds of insulin resistance to an even greater degree than would have been expected based on their individual contributions," he said.
Low levels of vitamin D have been linked to many health problems, including diabetes, heart disease, depression, and dementia.
"It's not clear whether obesity itself causes a low vitamin D level or if it's the other way around," said Dr. Liu.
Future research could look into whether vitamin D supplements could help obese people lower their risk of insulin resistance and diabetes. Vitamin D supplements could be a cheap and easy way to prevent diabetes, said the authors, especially when it can be difficult to lose weight.
While vitamin D supplements could be a useful prevention strategy, too much vitamin D can cause problems of its own, said Dr. Liu. Furthermore, low vitamin D is one of many diabetes risk factors.
"Therefore, to control diabetes, we need to have comprehensive prevention strategies," said Dr. Liu.
"For example, physical activity may be the most cost-effective way to control weight and subsequently to control conditions including diabetes and heart disease," he said.
The study involved 5,806 participants in the National Health and Nutrition Examination Survey (NHANES). It is the first study to look at the link between vitamin D and diabetes risk in obese people using a large, nationally representative sample of people.
The research was published June 29 in Diabetes Care, a journal of the American Diabetes Association.