The word 'vitamin' means something the body is unable to manufacture and must be obtained from food. Vitamin D is a hormone, a chemical that we make on our skin from sun exposure from a specific wavelength of light, UVB. Every decade our vitamin D production (per hour of sun exposure) goes down and of course where live is an important aspect to obtaining Vitamin D from sun exposure. Vitamin D is a group of fat-soluble secosteroids which controls calcium levels in the blood by promoting calcium absorption in the gut to maintain adequate serum calcium and phosphate concentrations to enable normal mineralization of bone It is also needed for bone growth and bone remodeling (very important for us joint replacement folk) by immune cells such as osteoblasts and osteoclasts. Without sufficient vitamin D, bones can become thin, brittle, or misshapen. It is crucial for bone and muscle development, and for preventing osteoporosis. Together with calcium, vitamin D also helps protect older adults from osteoporosis. For us humans the most important related compounds of vitamin D are vitamin D2 and vitamin D3. Very few foods in nature contain vitamin D. The flesh of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources. Small amounts of vitamin D are found in beef liver, cheese, and egg yolks. Vitamin D in these foods is primarily in the form of vitamin D3. It is a very wise idea to get your Doctor to check your Vitamin D levels. if you are prescribed a supplement, you may experience cramps in your legs or headaches when you start taking them. This can be caused by low Magnesium. Try eating a handful of sunflower seeds, providing you are not sensitive to seeds. Cheers, Poppet. Disclaimer: The information on dietary factors, foods, and beverages contained in this article does not cover all possible uses, actions, precautions, side effects, and interactions. It is not intended as medical advice for individual problems. Liability for individual actions or omissions based upon the contents of this article is expressly disclaimed. Consult a doctor or other health care professional for diagnosis and treatment of all medical conditions including the taking of supplements.