HARVARD GAZETTE ARCHIVES

Evidence is piling up that boosting vitamin D intake may help prevent breast cancer. One major study of 1,760 women found that the higher the levels of vitamin D in a woman's blood, the less the risk of breast cancer. Those who boasted the highest levels (more than 52 nanograms per liter) cut their risk of breast cancer in half compared with women with the lowest amounts (less that 12 nanograms per liter).

On the basis of such studies, nutrition experts have started to recommend that adults get 800-1,000 international units (IU) of the vitamin every day, up from the 400 IU, the standard for women 50-70 years old.

An article in the June issue of Women's Health Watch, published by the Harvard Medical School, suggests that women can easily up their daily D dose with a combination of sunlight, diet, and supplements.

Anyone who gets enough sun doesn't need to worry about getting enough of the vitamin. It's a hormone that is made in skin by exposure to ultraviolet rays. However, sun doesn't come easily in places like New England and the Pacific Northwest. There's also a worry of increasing the risk of skin cancer. Sunscreens cut that risk, but they also block the ultraviolet B rays that drive the skin to make vitamin D.

The Harvard article points out, "You can get adequate vitamin D from 10 to 15 minutes of sun a couple times a week, without sunscreen, on the face, arms, and hands." Many experts see little cancer risk in that much exposure. For longer periods in the sun, use sunscreen.

You may need to spend more time in the sun if your skin is dark or you are older. The darker your skin, the more sun exposure it requires to produce D. The older your skin, the less able it is to manufacture the vitamin.

Getting more Ds

To supplement sun, some foods are good sources of the vitamin. Salmon, mackerel, and other fatty fish provide D directly. Fortified foods, like milk and some cereals, add to the intake. Fortified milk also builds stronger bones and teeth, and supports the work of the nervous system and muscles.

Multivitamin tablets include D; check the label to see how much. If it's not enough to reach levels of 800-1,000 IU, add a vitamin D supplement. The latter usually contain 400 IU. If you also take calcium tablets, check to see how much vitamin D they might add.

Don't overdo it, warn the Harvard experts. Too much D from supplements can cause an unhealthy buildup of calcium in the body's tissues. The tolerable upper limit is 2,000 IU a day.

Another warning: Don't add cod liver oil to your D supplement intake. The oil contains large quantities of vitamin A, high levels of which can harm your bones.