Has the recommended amount of vitamin D for adults been increased recently?
The current guidelines for vitamin D were refined in 1997 in the Institute of Medicine's "Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride." At that point, the recommendation established was 200 International Units (IU), or 5 micrograms, of vitamin D a day for anyone 50 or younger; 400 IU or 10 micrograms for those aged 51-70; and 600 IU or 15 micrograms for those 71 and older.
More recently, you may have heard about an article in the September 2007 issue of Archives of Internal Medicine, which indicated that the current recommended amounts may be too low for many people. Some experts are suggesting intakes of 800 to 1,000 IU a day, especially for people who are more at risk of having chronically low levels of vitamin D in their bloodstream.
Vitamin D is unique in that the body's skin actually produces it when exposed to the sun. Some researchers suggest that five to 30 minutes of direct sun exposure mid-day at least twice a week to the face, arms, legs or back usually is sufficient. But during the winter, many people don't get that much sun exposure. And, people with dark skin have a more difficult time converting sunlight to vitamin D. Use of sunscreen also prevents the skin from absorbing the ultraviolet rays necessary for vitamin D production.
In addition, older people can't synthesize vitamin D as easily. And, people who are obese also have trouble with maintaining adequate vitamin D levels. A fat-soluble vitamin, vitamin D appears to become trapped in fat tissue, limiting its availability in the bloodstream.
Having enough vitamin D appears to be more important than we previously thought. Always known for its ability to strengthen bones, there's growing evidence that adequate amounts of vitamin D may help reduce the risk of diabetes, multiple sclerosis, high blood pressure and some types of cancer.
It's hard to get too much vitamin D, but it is possible. Upper intakes are currently listed at 2,000 IU or 50 micrograms a day, but some researchers believe most people could consume five times that amount with no harm.
Few foods are naturally high in vitamin D, with the exception being fatty fish such as salmon, tuna and mackerel. Most people get vitamin D from fortified foods, such as milk, cereal and orange juice.
Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH, 43210-1044, or filipic.3@cfaes.osu.edu.
Editor: This column was reviewed by Julie Shertzer, registered dietitian and program specialist for Ohio State University Extension in the Department of Human Nutrition, in the College of Education and Human Ecology.