A comprehensive review of the evidence suggests that low vitamin D levels are not a cause but a consequence of ill health, casting strong doubt on the value of vitamin D supplements to protect against acute and chronic disorders such as cancer, cardiovascular disease, diabetes, Parkinson's disease, and even death.

The findings of the large systematic review, published in The Lancet Diabetes & Endocrinology, challenge the prevailing wisdom among many scientists that vitamin D has a potential role in disease prevention, and will have important implications for nearly half of US adults who take vitamin D supplements at an overall cost of $600 million every year.

It is well known that vitamin D promotes the uptake of calcium and bone formation, but observational evidence also suggests a link between inadequate levels of vitamin D and greater risks of many acute and chronic diseases. But whether this is a cause-and-effect relationship is unknown, which has prompted large randomised trials to test whether vitamin D supplementation can reduce the risk of disease development..............

http://medicalxpress.com/news/2013-1...n-disease.html