Vitamin D deficiency is seen more in residents of the northeastern United States and people with more skin pigmentation. This deficiency is associated with increased risk of fractures and is beginning to be associated with increased risk of several types of cancer, including colon, breast, ovarian and prostate cancers.
The main marker used in testing for vitamin D deficiency is low serum 2, 5-hydroxy vitamin D [25(OH) D.] A serum level of 25(OH)D of 15-20 ng/mL is seen with osteoporosis. Levels below 30 ng/mL are associated with increased risk of colon cancer and levels above 150 ng/mL are potentially toxic.
The authors report that daily doses of vitamin D need to be higher than the current RDA. Sufficient vitamin D should be taken to elevate 25(OH)D above 30 ng/mL. A daily dose of 1,000 IU should do that and not cause toxicity.
In the United States the estimated daily sun exposure for a person to maintain a 25(OH)D level of 30 ng/mL is 15 minutes in the summer and 20 minutes in the early fall or late spring from 11:00 A.M. to 2:00 P.M.. Exposure should be to the arms, shoulders and back, while dark skinned people require twice as much exposure. North of the 37 degree latitude from November to March no amount of sun exposure is enough to maintain adequate vitamin D levels.
CONCLUSION: The authors review 63 studies that have been done of the protective effects of vitamin D against a number of different cancers. The studies show that vitamin D supplementation can reduce the risk and mortality of many cancers with very little cost. The National Academy of Sciences Institute of Medicine places the daily dose of vitamin D for an adult at 1,000 IU/day.
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