The Institute of Medicine brought experts together recently to explore the question of whether the RDA or recommended daily allowance, of vitamin D has been set too low. The impetus for the occasion was the mounting evidence for this vitamin's role in preventing common cancers, autoimmune diseases, type 1 diabetes, heart disease, and osteoporosis. Furthermore, studies have shown that vitamin D deficiency is common in the U.S.
Because the typical symptoms are aching bones and muscle discomfort, vitamin D deficiency is often misdiagnosed as fibromyalgia or chronic fatigue syndrome, according to Michael F. Holick, MD, PhD, of the Boston University School of Medicine. Dr. Holick has conducted a review of all vitamin D studies, which was published in the December 2004 issue of the American Journal of Clinical Nutrition. Vitamin D has become the vitamin of the moment, possibly because researchers in this field want to raise the RDA again. And Dr. Holick's review, which was funded by the U.S. National Institutes of Health, certainly supports the move.
For most Americans, sunlight provides the lion's share of our vitamin D requirements because we eat few foods that naturally contain vitamin D, such as cod liver oil and oily fish (salmon, sardines, and mackerel). But many Americans do not met the minimum requirement of sun exposure. What's more, vitamin D deficiency is more pronounced among people living at higher latitudes, such as the New England States, especially in winter. Dr. Holick and colleagues conducted a 2002 study at the Boston Medical Center, which found that, by the end of the winter, 32% of students and doctors, aged 18 to 29 years, were vitamin D deficient.
Winter isn't the only problem because, year-round, many people spend a lot of time indoors or slather themselves with sunscreen when they do go outside. So it was not too surprising that another study conducted in Boston found a high degree of D deficiency in white (30%), Hispanic (42%) and black (84%) elderly people at the end of August. Another study found that 38% of nursing home residents were vitamin D deficient. Much of the sun avoidance and excessive sunscreen use is attributed to public education campaigns by dermatologists warning about skin cancers. It should be noted, however, that the most deadly form of skin cancer, melanoma, is unrelated to sun exposure, as the disease usually occurs in areas of the body not exposed to the sun.
Obesity is yet another cause of vitamin D deficiency, according to Dr. Holick, who found that even when dietary vitamin D intake and sun exposure are adequate, the vitamin becomes unavailable because it becomes stored in the large amount of body fat. Aging skin requires more sun exposure. A 70-year-old exposed to the same amount of sunlight as a 20-year-old will only make 25% of the vitamin D that the young person can make. Breastfed infants are deficient in vitamin D because human milk is deficient in vitamin
D. Dr. Holick offered this explanation for why deficiencies are widely overlooked: During the standard blood work-up, doctors tend to focus on the blood calcium levels, and if they are normal, doctors incorrectly assume their patients are getting enough D. Why the seemingly sudden interest in vitamin D when intriguing research goes back over a half century? In 1949, a researcher published his observation that people who live at higher latitudes, such as New Hampshire, Vermont, and Massachusetts, had a higher incidence of cancer deaths, compared with people living in southern states, such as Texas, Georgia, and Alabama. In a telephone interview, Dr. Holick was asked why other researchers didn't pick up on this study and look further. "It was an interesting observation, but people didn't take epidemiology seriously," he answered. "Little attention was paid to it until the 1980s when other researchers reported that colon and breast cancer rates were higher for those living at higher latitudes in the U.S." Even then, the finding was not taken seriously until researchers understood the mechanism for how the breast, colon, and prostate activate vitamin D and use it to regulate cell growth, which Dr. Holick explained as a process that is, "keeping cell growth in check and possibly preventing the cell from becoming autonomous and developing into an unregulated cancer cell."
After the paper explaining the mechanism was published in the British journal The Lancet, much more research attention began to be paid to vitamin D. And after 1999, many more observational studies were published showing a link between vitamin D deficiency and several chronic diseases. For example, there are higher rates of multiple sclerosis in people who live at higher latitudes; and another study showed vitamin D intake is inversely associated with rheumatoid arthritis. In a 2001 study published in The Lancet, children treated with 2,000 IU daily of vitamin D from their first birthday onward had an 80% decreased risk of developing type 1 diabetes throughout the next 20 years. And in the last few years, several studies have been published indicating a link between schizophrenia and decreased exposure to sunlight.
Dr. Holick's review states that animal studies have successfully shown that type 1 diabetes, rheumatoid arthritis, and multiple sclerosis can be prevented using mice prone to these diseases. To Dr. Holick, who is an endocrinologist, it is clear from studies like these (and many more that go unmentioned in this article for lack of space) that vitamin D should no longer be thought of only as the nutrient necessary for the prevention of rickets in young children. He said that his work has been instrumental in the vitamin D fortification of several common foods, including milk products, bread, and orange juice.
In the telephone interview, Dr. Holick was asked whether an increase in the RDA for vitamin D was imminent, given the fact that the Institute of Medicine, a division of the National Academy of Science, recently held a meeting on the topic. "No, it usually takes 10 to 15 years to change an RDA," he answered. "A huge bureaucratic system is involved." In the meantime, he and other vitamin D researchers recommend a minimum of 1,000 IU vitamin D daily. This increase, he explained, will maximize the absorption of calcium. As for the risk of overdose, Dr Holick said, "You'd have to take 10,000 to 20,000 IU daily to approach toxicity." Is the type of vitamin D important? "Multivitamins usually have D2 which comes from yeast, but it's probably only 20-40% as effective as D3," which, he believes is better and longer lasting. Then there's the question of what constitutes an adequate amount of sunlight: "Five to ten minutes of exposure of the arms and legs or the hands, arms and face two or three times a week," stated Dr. Holick, adding a way of determining the right timing, "25% of the time that it would take to cause a light pinkness to the skin."
For More Information: Read Dr. Holick's book, co-authored with Mark Jenkins and written for the general public, The UV Advantage (New York: Simon & Schuster/ ibooks, 2003). Copyright Center for Medical Consumers Source: HealthFacts