Vitamin D is a fat-soluble vitamin. It's not found in many foods unless they have been fortified with it. Normally, your body makes vitamin D when your skin is exposed to sunlight.
Vitamin D is required by your body to absorb and utilize calcium, which keeps your bones and teeth strong. A vitamin D deficiency leads to weakened bones and rickets in children and osteomalacia in adults.
Although sunlight exposure is the main source, the Institute of Medicine has set a daily requirement for dietary vitamin D.
- Up to age 70: 600 International Units (IUs) per day
- Ages 71 and older: 800 IUs per day
Observational studies indicate that having insufficient levels of vitamin D may be correlated with an increased risk of cancer, multiple sclerosis, diabetes and high blood pressure.
Vitamin D is found naturally in oily fish. It's also added to milk, soy milk and breakfast cereals.
Supplements may be beneficial for many people, especially during the winter or if you normally avoid sun exposure. Vitamin D is usually added to calcium supplements to increase calcium absorption in order to prevent osteoporosis.
Taking vitamin D supplements in large doses for extended periods of time may result in vitamin D toxicity, so the Institute of Medicine determined tolerable upper levels to be:
- Ages 1-3: 2500 IUs per day
- Ages 4-8: 3000 IUs per day
- Ages 9 and above: 4,000 IUs per day
"Dietary Supplement Fact Sheet: Vitamin D." National Institutes of Health. Updated 08/2007.
Otten JJ, Hellwig JP, Meyers LD. "Dietary Reference Intakes: The Essential Guide to Nutrient Requirements." IOM, 2006.