New research makes the case that vitamin D helps protect older women against rheumatoid arthritis -- an autoimmune joint disorder of unknown cause. Recent studies have also linked deficiencies of vitamin D to other disorders such as certain cancers, heart disease, diabetes, and even unexplained pain but its role in human autoimmune disease is less clear.
The studies are far from conclusive, but researcher Michael Holick, MD, says there is every reason to believe that the supplement plays a much bigger role in disease prevention than has been recognized.
"Vitamin D has always been considered sort of a ho-hum vitamin," Holick tells WebMD. "People think they get plenty of it from the sun or in their diets, but these days that just isn't the case."
Vitamin D and Rheumatoid Arthritis
The latest research drew on data from the Iowa Women's Health Study, which followed almost 30,000 women, aged 55 to 69, for 11 years. Over the course of the study, the women were questioned about their eating habits, their use of nutritional supplements, and other health-related issues.
Women who got less than 200 international units (IU) of vitamin D in their diets each day were 33% more likely to develop rheumatoid arthritis than women who got more, researcher Kenneth G. Saag, MD, tells WebMD. Saag is an associate professor of medicine at the University of Alabama at Birmingham.
The association remained significant even after the researchers adjusted for other suspected rheumatoid arthritis risk factors, such as smoking. And even though many foods with vitamin D are also high in calcium, the vitamin's protective effect seemed to be independent of how much calcium the women ate.
The findings are reported in the January 2004 issue of the journal Arthritis and Rheumatism.
How Much Is Enough?
An 8-ounce glass of milk or fortified orange juice has about 100 international units (IU) of vitamin D and a typical multivitamin has 200 to 400 IU. Other good dietary sources of vitamin D include cod liver oil, which has 1360 IU of vitamin D per tablespoon; salmon, which has 425 IU per 3-ounce serving; and herring and sardines. The recommended intake of adequate amounts of vitamin D depends on a person's age. The Food and Nutrition Board (FNB) of the Institute of Medicine says that older women should consume 400 to 600 IU per day in order to have adequate vitamin D intakes.
Like Holick, Saag says he believes vitamin D deficiency is an under-recognized health problem in the U.S. today.
"General population studies indicate that about one in three people are vitamin D deficient," he says. "This is a particular problem during the winter months, when sun exposure is minimal. This is another reason why people should think about supplementing their diets with a multivitamin."
But Holick says most people need to take 1000 IU of vitamin D each day. And he says even this amount may be inadequate in people who have no exposure to the sun.
"Most people get between 90% and 95% of their vitamin D from sun exposure, so if you eliminate that you are setting the entire country up for vitamin D deficiency," he says.
The director of the Vitamin D Research Lab at Boston University, Holick advocates a limited amount of sun exposure, without sunscreen, every day -- a message that the nation's top dermatology group abhors. In a recent press release, officials with the American Academy of Dermatology expressed "deep concern" that the public is being misled "about the very real danger of [unexposed] sun exposure -- the leading cause of skin cancer."
But Holick counters that it does not take much sun to get more than enough vitamin D -- only a few minutes of unprotected sun exposure at most for most people.