The virtues of vitamin D

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The virtues of vitamin D

What’s special about vitamin D? This fat-soluble vitamin is exceptional among vitamins in three ways. First, it has a unique mechanism of action in the body. Second, you can’t get very much of it naturally through your diet. And third, many Americans are deficient in this vital nutrient.

That final point is keenly important, in light of burgeoning evidence that vitamin D’s health benefits extend far beyond its reputation for building healthy bones. Over the past decade, studies suggest that adequate amounts of vitamin D may lessen the risk of several types of cancer and may also play a role in preventing high blood pressure, multiple sclerosis, and even schizophrenia. And a 2007 meta-analysis of 18 randomized controlled trials showed that vitamin D supplementation may even help people to live longer.

How vitamin D helps

Heart and blood vessels. Low levels of vitamin D have been linked to high blood pressure in several studies, but further research is needed to determine whether consuming additional vitamin D—either in food or pills—lowers blood pressure or heart attack risk.

Cancer. Higher blood levels of vitamin D have been linked to a lower risk of colon, prostate, breast, and lung cancers, along with lower mortality from some of these cancers. A 2007 study in The European Journal of Cancer compared cancer rates in sunny countries with those in less sunny climes. The study, which involved 13 cancer registries with over four million people, showed that vitamin D production in the skin (which occurs with exposure to sunlight) may lower the risk of several forms of cancer, especially stomach, colorectal, liver and gallbladder, pancreas, lung, breast, prostate, bladder, and kidney—but only in people who live in sunny regions.

Bones. Like calcium, vitamin D plays a crucial role in keeping your bones healthy. In fact, taking calcium to shore up bones does little good if your vitamin D levels are insufficient. Research has shown that, in older people, taking 700 to 800 IU per day of vitamin D appeared to reduce the risk of hip fracture and any nonvertebral fracture, but doses of 400 IU did not.One additional way vitamin D may help reduce fractures is by preventing the falls that can cause them. Vitamin D deficiency leads to muscle weakness, but getting enough can improve muscle function. A study of nursing home residents found that, over a five-month period, people who took 800 IU of vitamin D per day were 72% less likely to fall and fell less often than people who took a dummy pill. Lower doses of vitamin D did not offer the same protective effect.

How much D do you need?

The recommended dietary intake of vitamin D goes up as people age, from 200 IU daily for ages 19 to 50, to 400 IU for ages 51 to 70, and 600 IU for those 71 and older. However, most experts recommend getting at least 1,000 IU of vitamin D per day.

If you avoid the sun, live in the northern latitudes, are elderly, or have darker skin, you might benefit from even more vitamin D. The current RDA of 400 IU raises the amount of vitamin D circulating in the blood only slightly. Depending on how much a person started out with, a daily intake of about 2,000 IU—the upper limit set by the National Academy of Sciences—is necessary before blood levels get high enough for vitamin D to have its full disease-fighting effects.

How to get more vitamin D

So, how can you get 1,000 IU of vitamin D a day? You could eat vitamin D–rich foods, like fatty cold-water fish and fortified foods, which include breakfast cereals and some juices in addition to milk, but you’d have to eat an awful lot to raise your blood levels. Getting more sun exposure is another way to increase vitamin D levels, but doing so means raising your risk for skin cancer and other forms of skin damage. Some analysis shows that any increase in skin cancer from adding a small amount of unprotected sun exposure would be offset by declines in other forms of cancer. But again, you are limited by your latitude.

Unless you live in the South and spend a fair amount of time outdoors, some kind of supplement is the answer. Most multivitamins contain 400 IU of vitamin D. But you shouldn’t just take two, because the vitamin A in the pill may interfere with the vitamin D.

Many calcium pills contain about 200 IU of vitamin D, so a multivitamin and three calcium pills would get you to 1,000 IU. For women, that’s not a bad way to go. For men, it may be risky because of the possible link between high calcium intake and prostate cancer.

That leaves vitamin D pills. A daily 1,000-IU supplement should take care of your minimum needs. If your multivitamin contains some vitamin D, but less than 1,000 IU, you can take a separate vitamin D supplement to make up the difference.

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