Like many vitamins, vitamin D is versatile. It has long been 
associated with bone development, but severe deficiency can result in 
diseases, such as rickets. Recent studies found some correlation between
 vitamin D levels and cardiovascular health, the development of multiple
 sclerosis, tuberculosis infection and now pre-menopausal breast cancer.
 Researchers at the San Diego School of Medicine of the University of 
California have found that low levels of serum (blood) vitamin D are 
associated with a crucial period of tumor formation for breast cancer.