Low vitamin D levels are more common in women than in men. Low vitamin D levels have been implicated in numerous disease processes including fracture risk, falls, cardiovascular disease, hypertension, diabetes mellitus and cancers. In this article we review recent evidence regarding associations between low vitamin D levels and cancers and cardiovascular disease. We also review evidence regarding associations between high vitamin D levels and vascular calcifications and pancreatic cancer. It appears that there is probably an optimal level of vitamin D that is neither too high nor too low that is required to maximize health. On going clinical trials should aid in elucidating the optimal levels of 25-hydroxyvitamin D for numerous health outcomes.