Creighton University researcher Joan Lappe says during the summer months, the body can convert solar energy into ample amounts of vitamin D with just 10 to 15 minutes daily exposure.

"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 said in a release. "What that means is most of us are deficient in vitamin D this time of year."

Vitamin is in fish oil and a few fortified foods, but it's difficult to take in adequate amounts of vitamin D by eating alone, however, the amount of a vitamin D supplement is subject to debate, Lappe says.

The U.S. government's recommended daily allowance is 200 IU until age 50, 400 IU for those age 50 to 70 and 600 IU after age 70

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