Studies indicate vitamin D might help people live longer

Vitamin D is best known for building strong bones, but it may have another benefit: longevity.

In a recent analysis of more than 18 studies involving nearly 60,000 people, those who took vitamin D supplements had a 7 percent reduction in mortality from all causes compared to those who didn't take the vitamin.

"The results are remarkable," notes Edward Giovannucci of the Harvard School of Public Health in an editorial published in the Archives of Internal Medicine, where the study also appeared this month.

Even better, the study found no "negative surprises" from taking vitamin D, as long as doses were kept between 300 to 2,000 international units per day.

That's key because the recent excitement over the health benefits of vitamins has been tempered by sobering results: Scandinavian researchers found that smokers who took beta-carotene had an increased risk of developing lung cancer compared with those who didn't take the supplements.

These new findings add to the growing interest in vitamin D, often dubbed the "sunshine vitamin" because the skin needs the sun's ultraviolet rays to make it.

Vitamin D is crucial for immunity. It prompts the production of antimicrobial substances that seem to act as natural antibiotics and antiviral agents. Some experts think that the reduced sun exposure during winter months could help account for the seasonal ebb and flow of colds and influenza.

"It's always been a mystery why influenza disappears in the summertime," notes John J. Cannell, a physician who heads the nonprofit Vitamin D Council.

Emerging research also points to a role for vitamin D in cancer prevention, particularly against breast, colon, prostate and lung tumors. Vitamin D also could help with cancer treatment.

Another possible benefit of vitamin D is prevention of Type 2 diabetes, which now affects an estimated 17 million Americans. And in an upcoming paper, Cannell proposes that vitamin D deficiency during pregnancy may play a role in the worldwide increase of childhood autism.

So how could one vitamin have so many potentially wide-ranging effects? Unlike other vitamins, D acts both as a vitamin and as a hormone that can be activated as needed by the body.

This wider role of vitamin D has led scientists to weigh increasing the current recommended daily intake. Many experts now suggest checking vitamin D blood levels to detect deficiencies before they produce symptoms. Others caution that doing so is too costly and uncertain, because testing costs at least $100 and there are no standards for optimal blood levels.

"At the moment, it's really difficult to be able to pinpoint whether a particular level can be used in all circumstances to say this person has the best level of vitamin D that they can have," notes Ann Prentice, director of the British Medical Research Council's Human Nutrition Research laboratory.

To cover the bases, here's how you can make sure you get enough vitamin D:

* Eat salmon or mackerel. Just 3.5 ounces of either provides 90 percent of the daily value for vitamin D. Other foods naturally rich in vitamin D include sardines, tuna, eggs and liver. Foods fortified with vitamin D include milk, margarine and some ready-to-eat breakfast cereals.

* Grab a few rays. Emphasis here is on "few," because prolonged sun exposure increases risk of skin cancer significantly. Just 20 minutes of sun exposure without sunscreen enables the skin to produce about 20,000 IU of vitamin D.

"You'd have to drink about 400 glasses of milk to get that same amount," Cannell notes. And unlike megadoses of dietary supplements, sun exposure does not appear to produce vitamin D toxicity.

* Take a vitamin D supplement. The question is how much should you take? The National Academy of Sciences sets 200 IU per day as the adequate intake for those aged 19 to 50; 400 IU for people 51 to 70; and 600 IU for those 71 and older. In the study that showed a 7 percent reduction in mortality, the average intake was about 500 IU per day.

Too much vitamin D can be toxic, the reason why the National Academy of Sciences sets 2,000 IU per day as the tolerable upper limit for adults. (Signs of toxicity begin at about 10,000 IU daily.)

Multivitamins provide vitamin D but the amount varies widely, so read the labels: Men's One-A-Day contains 400 IU; Centrum Silver has 500 IU; Women's One-A-Day contains 800 IU; while Nature Made multivitamins provide 1,000 IU.

Many calcium supplements also contain vitamin D, providing between 200 to 400 IU. And single vitamin D supplements are another option. Just make sure that the combination of dietary supplements and food sources of vitamin D don't exceed the upper limit.

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