Winter and vitamin D

Nov 16 2007

As the days grow shorter, the sun's warm rays aren't the only thing your body may be missing, warns Creighton University researcher Joan Lappe, Ph.D.

If you live in North American at latitudes above the 37th parallel – Omaha is near the 41st parallel - you also may not be getting enough vitamin D, says Lappe, professor of medicine and holder of the Criss/Beirne Endowed Chair in the Creighton School of Nursing.

And that vitamin D is important to your health. In fact, a landmark study by Lappe and other Creighton researchers, published in June in the American Journal of Clinical Nutrition, showed a direct link between vitamin D and cancer prevention. Humans can get vitamin D from several sources.

During the summer, the body can convert solar energy into ample amounts of vitamin D with just 10-15 minutes exposure daily to the sun. That's not possible this time of year.

“From October until the end of March, the angle of the sun is such that, in much of North America, no vitamin D is available from that source,” Lappe says. “What that means is most of us are deficient in vitamin D this time of year.”

While you can get the vitamin from fish oil and a few fortified foods, it's difficult to take in adequate amounts of vitamin D by eating alone. Lappe recommends taking vitamin D3 – the same form of the vitamin that humans make from exposure to the sun.

The amount of vitamin D you should take daily is a subject of great debate, Lappe notes.

The U.S. government's recommended daily allowance is 200 IU until age 50, 400 IU for 50-70 year olds, and 600 IU after age 70. However, many medical experts believe those recommendations are way too low.

The Canadian Cancer Society recently recommended that people with light skin take 1,000 IU of the vitamin supplement during fall and winter, while people with darker skin or limited sun exposure take that amount throughout the year.

The society's recommendation coincided with the publication of the Creighton (Cray-ton) research in June. The four-year study involving 1,179 Nebraska women showed that women taking calcium supplements plus 1,100 IU of vitamin D3 daily, experienced a 60 percent decrease in their risk of developing cancer than a placebo group.