Nearly 75-percent of the US population is Vitamin D deficient. Experts say it is rarely possible to consume adequate amounts through the main dietary sources of Vitamin D, including wild-caught oily fish, fortified milk and baby formula, cereal and orange juice. In addition to inadequate bone development and excessive bone loss, studies indicate that the effects of a Vitamin D deficiency include an elevated risk of developing (and dying from) cancers of the colon, breast and prostate; high blood pressure and cardiovascular disease; osteoarthritis; and immune-system abnormalities that can result in infections and autoimmune disorders like multiple sclerosis, Type 1 diabetes and rheumatoid arthritis.