Where research once suggested a limited health role for vitamin D, today there is increasing evidence that it protects against breast, colon and prostate cancer. Population studies show that people with the highest vitamin D levels are less likely to develop multiple sclerosis, lupus, rheumatoid arthritis and other autoimmune diseases than those with lower levels. Plus it appears that vitamin D may protect against heart disease, type 2 diabetes and the insulin resistance that precedes it.
"If just half the chronic diseases laid at the feet of vitamin D pan out, it will be quite significant," said Robert P. Heaney, a professor of medicine at Creighton University in Omaha and a proponent for increasing vitamin D intake.
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Just a decade ago, scientists developed an inexpensive blood test that more accurately determines vitamin D status. Use of that test revealed widespread deficiencies and led the NAS to note in 1997 that vitamin D "deficiency is now a significant concern in adults over the age of 50 years who live in the northern industrialized cities of the world."
In 2004, the dietary guidelines scientific committee concluded the elderly, people with dark skin and those exposed to insufficient sunlight "are at risk of being unable to maintain vitamin D status" and may "need substantially more than" the 1997 recommendations called for.
But some doctors worry that the evidence is still preliminary. Few if any studies "show that people are having problems with the lower limits of vitamin D being where they are," said New York University dermatologist Darrel Rigel, a past president of the American Academy of Dermatology.
Dermatologists are particularly concerned that raising the vitamin D recommendation might tempt some people to spend more time in the sun or in tanning booths, thus increasing their risk of skin cancer. "Our recommendation is to take either vitamin pills or eat food that we know has higher levels of vitamin D," rather than increase sun exposure, said Henry Lim, chairman of dermatology at the Henry Ford Hospital in Detroit.
Here's how to boost vitamin D levels safely:
Drink vitamin D fortified beverages. While diet alone is unlikely to get you to the levels needed, drinking milk and other vitamin D fortified beverages will help. Some juice and soy milk is also fortified. An 8-ounce glass of any of these beverages delivers about 100 IU, or about half the intake recommended daily for adults 19 to 50 years of age; a quarter of the amount for adults 51 to 70; and just a sixth of the intake for those 70 and older. Yogurt and cheese are not fortified with vitamin D.
Eat more herring and sardines. An ounce of pickled herring has nearly 200 IU of vitamin D. Two small sardines have 65 IU. But not all fish contains vitamin D. Salmon and tuna, for example, have none.
Breakfast on fortified cereal or cereal bars. A cup of vitamin D fortified cereal delivers about 40 to 60 IU of vitamin D. Fortified cereal bars have even less: about 30 IU per bar.
Take a multivitamin or other supplement. Most multivitamins, even the ones aimed at seniors, provide 400 IU of vitamin D, which won't cover those 70 and older. Some vitamin and health food stores sell gelcaps of vitamin D supplements that range from 700 IU to 2,000 IU. "The most practical way to increase our vitamin D levels is from supplements," said Harvard's Willett.
Fun in the sun. Fifteen minutes of peak sun exposure without sunscreen allows a light-skinned person to make about 20,000 IU of vitamin D, according to Hollis. But much of that dose quickly "goes away," he said. You'd need such exposures at least every few days in order to sustain adequate levels. Since regular sun exposure increases skin cancer risk, "it's okay to expose yourself a little to the sun," said Henry Ford's Lim, "but not too much."
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