Vitamin D Deficiency: Common Cause of Many Ailments?

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02-16-2005 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.

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 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.

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