Vitamin D is a fat-soluble vitamin. But it's not found in many foods unless they have been fortified with it -- like milk, yogurt, soy milk and breakfast cereals. Small amounts of vitamin D are found in oily fish and beef liver.
Normally, your body makes vitamin D when your skin is exposed to sunlight. It only takes about 5 to ten minutes a few times each week -- after that it's important to use sunscreen.
Your body needs vitamin D in order to absorb and utilize calcium, which keeps your bones and teeth strong, and is essential for normal blood clotting and muscle and nerve function.
A vitamin D deficiency can happen if you don't get enough sun exposure, if your kidneys cannot convert the storage form to the active form, or if you can't absorb vitamin D from due to problems with your digestive system. A longstanding lack of vitamin D leads to weakened bones and diseases called rickets in children and osteomalacia in adults.
The Institute of Medicine at the National Academy sets daily dietary reference intakes for vitamins and minerals. Although sunlight exposure is the main source, the IOM has set a daily requirement for dietary vitamin D that's based on age. It's the same for both males and females.
These DRIs represent an amount needed by a healthy person, so if you have any health issues, you should consult your health care provider.
Dietary Reference Intakes
- 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.
But so far, taking supplements with the idea of treating these conditions hasn't been shown to be beneficial.
Vitamin D supplements may be beneficial for some people, especially during the winter or if you normally avoid sun exposure. In fact it's usually added to calcium supplements. You can choose from two forms -- vitamin D2 or vitamin D3. Your body absorbs vitamin D a little better, but research shows that either form will give you enough vitamin D.
Taking large doses of vitamin D supplements for extended periods of time may result in vitamin D toxicity, so the Institute of Medicine the determined tolerable upper levels. Long-term use above these amounts might cause tissue calcifications that may result in damage to the heart, blood vessels, and kidneys. Don't use large doses of vitamin D supplements without speaking with your doctor first.
Tolerable Upper Limits
- Ages 1-3: 2500 IUs per day
- Ages 4-8: 3000 IUs per day
- Ages 9 and above: 4,000 IUs per day
Institute of Medicine of the National Academies. "Dietary Reference Intakes -- Vitamins." Accessed June 28, 2014. http://www.iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Vitamins.pdf.
National Institutes of Health, Office of Dietary Supplements. "Vitamin D - Health Professional Fact Sheet." Accessed June 28, 2014. http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/.
Otten JJ, Hellwig JP, Meyers LD. "Dietary Reference Intakes: The Essential Guide to Nutrient Requirements." IOM, 2006.