June 28, 2011 (San Diego) -- Vitamin D may help prevent diabetes in people at high risk of developing the condition, researchers report.
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.
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.