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Health Options
Alan Titchenal |
Here is some sunny news
about an essential vitaminIf a person claims to be a nutrition expert and says that your skin can carry out the photosynthesis of a vitamin that can prevent cancers, Type 1 diabetes, heart disease, osteoporosis and possibly even fibromyalgia, multiple sclerosis and high blood pressure, you might suspect that he is some type of quack. To add more ammunition to your suspicions, this person even claims that the recommended adequate intake values set for this vitamin in 1997 by the Institute of Medicine are inadequate.
Surprisingly, this person is no quack, and he has nothing to sell you but sunshine. Dr. Michael Holick, director of the Vitamin D, Skin and Bone Research Laboratory at the Boston University Medical Center, is a professor of medicine, dermatology, physiology, and biophysics. Dr. Holick is one of the world's top experts on vitamin D and served on the Institute of Medicine committee that set the recommended intake for vitamin D that he now considers to be too low.
QUESTION: How can vitamin D be related to so many health problems?
ANSWER: The association between vitamin D and osteoporosis has been known for a long time because vitamin D is needed for normal absorption of calcium from the intestine and for normal bone health. In addition to bone health, vitamin D is now known to play important roles in cell growth, immune function, blood pressure and insulin production. Due to these multiple roles in the body, inadequate vitamin D is potentially involved in a number of health problems.
Q: What are the sources of vitamin D?
A: When the skin is exposed to ultraviolet B radiation of sunlight, a form of cholesterol is converted to vitamin D. However, people who do not have adequate exposure to sunlight require a dietary source of vitamin D. Food sources include oily fish like salmon, milk and some breakfast cereals and orange juices that are fortified with vitamin D.
Q: How much vitamin D does Dr. Holick recommend?
A: The sun exposure needed for the skin to produce adequate amounts depends on the time of year, the latitude and a person's skin color. In a sunny location like Hawaii, five to 10 minutes of midday sunlight on the arms and face or legs two to three times a week is adequate to produce enough vitamin D in people with light-colored skin. People with darkly pigmented skin have a built-in sunscreen and can require 10 to 50 times the sunlight exposure to produce the same amount of vitamin D.
Q: What about people who do not get any sun exposure?
A: For those with no sun exposure, Holick recommends at least 1,000 IU of vitamin D per day. A typical multivitamin supplement with 100 percent of the Daily Value for vitamin D contains 400 IU. But, do not take two multiple vitamin dietary supplements just to get more vitamin D. If you did, Holick warns, this would provide too much vitamin A and increase the risk of birth defects and osteoporosis.
Q: How much vitamin D is too much?
A: The body has mechanisms to prevent vitamin D toxicity from too much sun exposure. To prevent toxicity from dietary or supplemental vitamin D, the Institute of Medicine set a tolerable upper intake level of 2000 IU per day from food and supplements combined.
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Alan Titchenal, Ph.D., C.N.S. and Joannie Dobbs, Ph.D., C.N.S. are nutritionists in the Department of Human Nutrition, Food and Animal Sciences, College of Tropical Agriculture and Human Resources, UH-Manoa. Dr. Dobbs also works with the University Health Services and prepares the nutritional analyses marked with an asterisk in this section.