People with lower levels of vitamin D in their blood may be at greater risk of developing type 2 diabetes, according to research published in the journal Epidemiology this month.

Dr. Paul Knekt of the National Public Health Institute in Helsinki, Finland and colleagues found that men with the highest serum vitamin D levels were the least likely to have developed type 2 diabetes 22 years later.

Lack of vitamin D interferes with insulin secretion, and studies suggest a link between low vitamin D and diabetes, Knekt and his team note. But most research has been cross-sectional, meaning it only focused on a single time point. Prospective studies, which follow people over time, are a better way to investigate potentially causal relationships.

The researchers looked at men and women who were 40 to 74 years old and free of diabetes when they enrolled in a health examination survey. Investigators followed them for 22 years, during which time 412 developed type 2 diabetes.

Knekt and colleagues compared baseline levels of blood vitamin D in the 412 cases and 986 control individuals who remained diabetes free.

They found that men in the top fourth based on their blood levels of the vitamin were 72 percent less likely to have developed type 2 diabetes than men in the lowest quartile, after the researchers adjusted for body weight, physical activity and other factors.

No such relationship was seen for women.

Certain lifestyle and diet factors could also be partially responsible for the vitamin D-diabetes risk link, the researchers note, concluding: “Further studies are needed before firm conclusions can be made about the role of vitamin D in diabetes prevention.”

SOURCE: Epidemiology, September 2008.