Research is confirming that vitamin D deficiency is more common than suspected and may be causing health problems for millions. Are winter clouds, cold weather and aging giving you a vitamin D deficiency? Sun exposure on bare skin is the major source of vitamin D, but length of seasons, geographic latitude, cloud cover, smog, and sunscreens can reduce UV ray exposure and vitamin D synthesis.¹ In the winter, especially in northern climates, UVB rays from the sun may not be strong enough to make vitamin D in our skin. Dark-skinned people are at increased risk of D deficiency. Eating low fat foods, avoiding the sun, and not eating enough wild-caught, oily fish (our best dietary source of vitamin D) have all contributed to widespread vitamin D deficiency. 
 
Research has led the Canadian Cancer Society and the Canadian Dermatology Association to recommend increasing vitamin D intake to 1000 IUs daily for Canadian adults under 50. Higher vitamin D and calcium levels have been linked to lower risk for some cancers, including colorectal, breast and colon cancers.²
 
Vitamin D is well-known for its role in building strong bones and teeth¹, however a study published in The American Journal of Clinical Nutrition found that taking vitamin D supplements and calcium substantially reduces all-cancer risk in post-menopausal women. The researchers found that the higher the levels of vitamin D in the blood, the lower the relative risk of developing cancer. Another study suggests that women who consume more calcium and vitamin D may be less likely to develop breast cancer before menopause.^2,3
 
One study linked low vitamin D levels in mothers to a five-fold increased risk of pre-eclampsia, a serious complication in pregnancy. Other research shows more than HALF of otherwise healthy adolescents may be vitamin D deficient, increasing their risk for osteoporosis and other health problems later in life. Adults with low blood levels of vitamin D may be at higher risk for several types of cancer, as well as high blood pressure, diabetes and bone fractures.
 
Bones and Risk Reduction
Adequate vitamin D in childhood prevents rickets and in adults prevents osteomalacia (soft bones). Vitamin D deficiencies are also linked to muscle weakness as well as general aches and pains. To minimize health risks associated with UVB radiation exposure, while maximizing vitamin D benefits, supplementation combined with small amounts of sun exposure, is the recommended way to assure optimum levels of vitamin D.¹
 
With aging, less vitamin D is converted to its active form, and a deficiency can occur in older men and post-menopausal women. In a review of women hospitalized for hip fractures due to osteoporosis, 50 percent were found to have signs of vitamin D deficiency.⁴ Caffeine can increase bone loss, but increasing calcium and vitamin D intake may counteract this effect. 
 
References:

1. The Office of Dietary Supplements, http://ods.od.nih.gov/factsheets/vitamind.asp. 09/19/2007
2. Canadian Cancer Society, Canadian Cancer Society Announces Vitamin D Recommendation, June 08, 2007, http://www.cancer.ca/
3. Joan M Lappe, Dianne Travers-Gustafson, K Michael Davies, Robert R Recker and Robert P Heaney, "Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial." American Journal of Clinical Nutrition, June 2007, Vol. 85, No. 6, 1586-1591, © 2007 American Society for Nutrition
4. LeBoff MS, Kohlmeier L, Hurwitz S, Franklin J, Wright J, Glowacki J., "Occult vitamin D deficiency in postmenopausal US women with acute hip fracture." J Am Med Assoc, 1999; 251: 1505-11 [PubMed abstract]