Go on, head outside for a sunny spring walk: The vitamin D we get from everyday sunlight—as well as from fish, fortified milk, and supplements—may curb diabetes risk, suggests new research.

In the 17-year Finnish study, people with the highest blood levels of vitamin D reduced their chances of developing type 2 diabetes by 40 percent. Of the more than 4,000 people in the study, the 187 diagnosed with type 2 registered the lowest vitamin D levels, regardless of age, sex, or time of year.

The vitamin D effect remained even when the researchers controlled for education, smoking, body weight, blood pressure treatment, and exercise, though it weakened slightly.

Also interesting was a discovery that people who exercised the most also showed the highest vitamin D levels, says lead researcher Paul Knekt, PhD, of the National Public Health Institute in Helsinki.

Why might vitamin D be higher in exercisers? Is it due to more time jogging in the sun? A healthier, fish-rich diet in this health-conscious group? More vitamin D supplementation? Or might exercise itself affect the body’s vitamin D processing?

That’s all fodder for future research, says Knekt, as is the question of whether vitamin D can reverse type 2’s progression. “Similar studies should be replicated before we can make firm conclusions about the role of vitamin D in diabetes prevention,” Knekt says.

The findings were published in the October 2007 issue of Diabetes Care.