Q. I have read recently that low levels of vitamin D could make people more likely to get cancer. But I have also read that too much vitamin D is dangerous. Can you tell me what is an appropriate amount of this vitamin daily?
A. Although there is no clear evidence that low levels of vitamin D cause cancer, a number of studies have found that people with cancer are more likely to have low levels of this vitamin.
A recent study showed such a linkage: women with more aggressive breast tumors had lower levels of vitamin D in their bloodstreams. Other research found that men with low levels and those with high levels of vitamin D were both more likely to die of cancer (American Journal of Clinical Nutrition, October, 2010). In this study, the best blood levels lay between 18 and 40 nanograms per milliliter.
The appropriate level of vitamin D supplementation depends on an individual’s blood level. It might range between 800 and 4,000 IU per day. For more information about interpreting the blood test and how much you should take, we are sending you our Guide to Vitamin D Deficiency