Vitamin D: Enjoying its day in the sun

Should I be taking vitamin D? That question is on many people's minds these days. A study published by the American Journal of Public Health in late 2005 concluded that taking vitamin D pills could substantially reduce the risk for breast, colon, prostate, and ovarian cancer.

Other positive findings

Over the past several years, there's been a steady accumulation of research showing a variety of health benefits from vitamin D. Moreover, the evidence isn't just for standard quantities, but for larger amounts, which would probably best be taken as vitamin D pills or as part of a multivitamin.

For example, there's a convincing body of evidence that vitamin D may be just as important as calcium for building bone strength and preventing osteoporosis. This makes perfect sense: One of vitamin D's main functions is to increase the absorption of calcium needed for the formation of bone.

Doctors have known that many body tissues other than bone have receptors for vitamin D, suggesting that the vitamin plays some role in the health of many tissues. For example, vitamin D seems important in building muscle strength. Several small studies hint that extra vitamin D confers cardiovascular benefits. There are also intriguing reports of protection against multiple sclerosis, rheumatoid arthritis, and other autoimmune conditions.

Not enough of those drops of golden sun

Natural food sources of vitamin D are scarce. You're basically limited to fat-rich fish that thrive in cold water: bluefish, mackerel, and salmon. Health officials recognized this problem years ago, when the main risk from a deficiency was rickets in children, and ordered the fortification of the food supply. In the United States, they picked milk as the vehicle. Each cup is supposed to contain 100 IU of vitamin D.

But for many people, the largest source of vitamin D is their own skin. When ultraviolet-B (UVB) light hits your skin, it turns a cholesterol-related compound into a preliminary form of the vitamin, which — several metabolic steps later — is rendered into vitamin D.

This dependence on sunshine presents several problems. In the warm, sunny months, there's skin cancer and damage to worry about. Sunscreens are a dilemma, because they block UVB light. And during the colder months, in many northern latitudes, UVB light is too weak to jump-start vitamin D production. Vitamin D researchers say lack of sunlight, and therefore the vitamin, may explain some north-south variations in disease rates. Fortunately, vitamin D is stored in fat, so Northeasterners do "bank" some of the vitamin during the sunnier months.

African Americans may have higher rates of some cancers because of vitamin D shortfall. The darker your skin, the less effective UVB is in starting the vitamin D conversion process. As a result, African Americans have, on average, about half as much vitamin D in their blood as whites.

The 1,000-IU pill

Adults should be getting 800–1,000 IU of vitamin D per day, not to exceed 2,000 IU daily. So how should you get 800–1,000 IU a day? Some kind of supplement is the answer. Many calcium pills contain about 200 IU of vitamin D, so a multivitamin and two calcium pills would get you to 800 IU.

May 2006 update

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