For the answer, we turned to Yale endocrinologist Elizabeth Holt, M.D., Ph.D., assistant professor at Yale School of Medicine. Dr. Holt writes:
“Vitamin D is needed to help calcium from your food reach the skeleton, where it keeps bones strong. Vitamin D is found in certain foods (fortified milk and cereals, oily fish, for example). In addition, your body will produce vitamin D when sunlight hits your skin during warm weather months.
“People at risk for vitamin D deficiency include the elderly, individuals with darker complexions, and those who avoid sunlight or vitamin D rich foods. The recommended daily allowance of vitamin D for adults is 600-800 international units (I.U.) daily. Higher doses of vitamin D are needed to start with for people whose levels are very low. Taking a vitamin D supplement is not necessary for everyone, but it is especially important for those who are at risk for vitamin D deficiency.
“Preliminary research studies have shown a role for vitamin D in cancer prevention. The dose of vitamin D needed for this benefit is not yet known.
“With vitamin D supplements, there is such a thing as ‘too much of a good thing.’ Vitamin D is stored in the fat tissue and is slow to leave the body when levels are too high. High levels of vitamin D in the body can have dangerous side effects. Therefore, it is not a good idea to take more than the recommended daily dose without a doctor’s supervision.”