Vitamin D supplements are typically used to guard against bone loss and fractures, but new research offers up another possibility: For folks with pre-diabetes, they may help lower the chances of a full diabetes diagnosis.
Across three clinical trials, investigators found that vitamin D supplements were modestly effective in curbing the risk of pre-diabetes progressing to type 2 diabetes. Over three years, just under 23% of study patients using vitamin D developed diabetes, versus 25% of those given placebo pills.
On average, the study found, supplements lowered the risk of progressing to type 2 diabetes by 15%.
“It’s pretty clear vitamin D has a moderate effect on reducing the risk of type 2 diabetes, if you’re at high risk,” said lead researcher Dr. Anastassios Pittas, of Tufts Medical Center, in Boston.
The findings do not apply to people at average risk of the disease, he stressed, and it’s still unclear what the optimal dose of vitamin D is for people with pre-diabetes.
Plus, Pittas said, no supplement would be a replacement for lifestyle changes, including a healthy diet and regular exercise.
“We don’t want the message to be, take a pill and you won’t need to do the hard work of changing your diet and exercising,” Pittas said.
Type 2 diabetes arises when the body’s cells no longer properly respond to the hormone insulin, which helps shuttle sugars from food into cells to be used as energy. As a result, blood sugar levels remain chronically high, which over time can damage the blood vessels and lead to heart, kidney and eye disease, among other complications.
Pre-diabetes is a state where blood sugar is abnormally high, but not yet high enough to diagnose type 2 diabetes. In the United States alone, about 96 million adults have pre-diabetes, according to the U.S. Centers for Disease Control and Prevention.
The vitamin D study started with the observation that diabetes prevalence is typically greater in places farther from the equator. That, Pittas said, hinted that sunlight exposure — which spurs the body to naturally produce vitamin D — might play a role in diabetes risk.
Subsequent studies found a link between people’s blood levels of vitamin D and their risk of type 2 diabetes. Meanwhile, lab research pointed to some potential reasons: vitamin D can, for instance, restore normal insulin production in animals.
So far, there have been three clinical trials that directly tested whether vitamin D supplements can lower the odds of pre-diabetes progressing to type 2. Each found that participants given vitamin D did have a somewhat lower risk, versus those given a placebo. But the difference was not significant in statistical terms, meaning the supplement could not be declared effective.
So Pittas and his colleagues conducted a “meta-analysis” that pulled together the data from all three trials. The idea is that, with a larger number of patients, it will be easier to detect a moderate effect of vitamin D.