Evidence is mounting that we may need even more -- especially older, dark-skinned, or housebound people.

According to the IOM Dietary Reference Intakes, the safe upper limit for vitamin D is 2,000 IUs for children, adults, and pregnant and lactating women. Some experts have suggested increasing the recommended amount to more than 2,000 IUs daily. But since vitamin D is a fat-soluble vitamin that is stored in the body, there's some concern it can be harmful in large doses.

"The current recommendations are not adequate to protect against chronic diseases or prevent osteoporosis," says Holick. "All evidence suggests that infants and adults can tolerate 1,000 IUs a day as safe, without risk of toxicity."

"Take a daily vitamin D³ supplement of 1,000 IUs or [get] safe sun exposure to maintain proper blood levels of vitamin D and reduce the risk of common cancers, type 1 diabetes, multiple sclerosis, rheumatoid arthritis, and inflammation associated with cardiovascular diseases," he suggests.

You're unlikely to get too much vitamin D in your diet unless you overdose on cod liver oil: "Read the label, and do not take cod liver oil if it contains vitamin A, because too much vitamin A can be toxic and weaken bones and cause birth defects in young women," Holick advises.

Sunlight will only produce as much vitamin D as you need, so there is no fear of overdosing from the sun, Holick says.

Boosting Vitamin D

Indeed, sunshine and supplements -- not food -- are the best sources of vitamin D, providing you choose a supplement with D³.

"Sunlight is the easiest, it's free, and your body is very efficient at making vitamin D from the sun, and it lasts twice as long as other sources," says Holick.

Good dietary sources are fortified foods such as milk, yogurt, margarines and cereals, catfish, sardines, salmon, tuna and egg yolks. But "it is hard to get enough vitamin D from your diet unless you enjoy dairy and fish, so it makes sense to try to get limited exposure to sunlight if you can and take a vitamin supplement," says Elisa Zeid, MS, RD, a spokesperson for the American Dietetic Association

Food for Thought

Chances are, you are not getting enough vitamin D for good health. So boost your D with safe sun exposure, or supplement your diet with 1,000 IUs of vitamin D³ a day. And be sure to eat a variety of foods rich in vitamin D. Also, check with your dermatologist about guidelines for safe sun exposure.

Originally published December 22, 2006.
Medically updated April 23, 2008.

SOURCES: Institute of Medicine Food and Nutrition Board, Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D and Fluoride. National Academy Press, Washington, D.C.,1999. Journal of Nutrition, Oct. 2005. Michael Holick, MD, PhD, professor of medicine, physiology, and biophysics, Boston University Medical Center. Elisa Zied, MS, RD, spokeswoman for American Dietetic Association; author, So What Can I Eat?! (Wiley, 2006). Eduardo Baetti, MD, rheumatologist, Kaiser Permanente, Atlanta.

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