The study does not prove cause and effect. "But if confirmed, there are huge implications because vitamin D is easy and inexpensive," Anastassios Pittas, MD, of Tufts Medical Center in Boston, tells WebMD.
Pittas presented the results here at the annual meeting of the American Diabetes Association.
Tracking Vitamin D Levels
The three-year study involved 2,039 people with high blood sugar levels. Their vitamin D levels were measured at the start of the study and six months, one year, two years, and three years later.
For every 5 nanograms per milliliter (ng/mL) increase in vitamin D levels, the risk of developing diabetes dropped by 8%, Pittas says. Levels of 30 or higher are considered normal.
The participants were divided into three groups. Participants in the group with the highest third of vitamin D levels (average reading of about 30 ng/mL) were 38% less likely to develop diabetes than those in the lowest third (average vitamin D level of 13 ng/mL).
A strength of the study is that vitamin D levels were measured at various time points, Pittas says. Past studies often relied on one measurement at the start of the study, which may not accurately reflect their vitamin D status over time.
The analysis also took into account a person's body weight, physical activity, and other factors known to decrease diabetes risk. Nonetheless, there could be some unmeasured variable that affected risk, Pittas says. He says a robust clinical trial in which half the people get vitamin D and half get placebo is needed to determine if supplements can stave off diabetes.
Sheena Kayaniyil, a PhD candidate at the University of Toronto, tells WebMD that her research also supports a role for vitamin D in the prevention of diabetes.
In a study of nearly 500 people at high risk of diabetes, higher vitamin D levels at the start of the study were associated with lower blood sugar levels three years later.
Higher vitamin D levels also predicted better function of the body's own insulin-producing beta cells at follow-up, she says. "Our research supports a potential role for vitamin D in the [development] of diabetes."
These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.