Vitamin D is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. It is also produced endogenously when ultraviolet rays from sunlight strike the skin and trigger vitamin D synthesis. In spite of the name, vitamin D is considered a prohormone and not actually a vitamin. This is because the body is capable of producing its own vitamin D through the action of sunlight on the skin, while vitamins are nutrients that cannot be synthesized by the body and must be acquired through the diet or supplements. Vitamin D has multiple roles in the body, helping to maintain the health of bones and teeth, support the health of the immune system, brain and nervous system, regulate insulin levels and aid diabetes management, support lung function and cardiovascular health and influence the expression of genes involved in cancer development. It also reduces risk of flu, reduced risk of diabetes and prevents cancer. The RDA is 600 IU for those 1-70 years of age and pregnant or breastfeeding women, and 800 IU for those over 71 years of age. An adequate blood level of vitamin D is 20 nanograms per milliliter, which can be achieved through daily skin exposure to sunlight. Levels over 50 nanograms per milliliter may cause side effects. The symptoms of vitamin D deficiency are sometimes vague and can include tiredness and general aches and pains. Some people may not have any symptoms at all. If one has a severe vitamin D deficiency he may have pain in his bones and feel weakness. He may also have frequent infections. However, not everyone gets these symptoms. Vitamin D toxicity, also called hypervitaminosis D, is a rare but potentially serious condition that occurs when someone has excessive amounts of vitamin D. Some other symptoms include high or low blood pressure, kidney problems and kidney stones, heart diseases or other heart problems, lung disorders, thyroid problems, liver disease, frequent headaches, stomach issues, skin disorders and musculoskeletal disorders.