As Vitamins Go, D, You Are My Sunshine
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 with those who didn't take the vitamin. The numbers improved slightly for people who took vitamin D for three years or more. They had an 8 percent lower risk of dying.
"The results are remarkable," notes Harvard School of Public Health's Edward Giovannucci 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 (IU) per day.
That's key because recent excitement over the health benefits of vitamins has been tempered by sobering results: Scandinavian studies, for example, found that smokers who took beta carotene -- converted in the body to vitamin A -- 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 in its natural form, the vitamin is produced by the skin under the sun's ultraviolet rays.
Beyond its proven bone benefits, vitamin D is critical for immunity, prompting production of antimicrobial substances that seem to act like natural antibiotics and antiviral agents.
Some experts think that the reduced sun exposure during winter 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 psychiatrist at Atascadero State Hospital in California 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 could help with cancer treatment. One recent study found that lung cancer patients who either got a lot of sun or had a high intake of vitamin D had three times the survival rate of their counterparts with lower vitamin D levels.
Another possible benefit of vitamin D is prevention of Type 2 diabetes, which affects an estimated 17 million Americans. And in an upcoming paper, Cannell speculates, based on population studies, 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 whether the current recommended daily intake is high enough. In the meantime, a growing number of experts, including Harvard's Giovannucci, advise routine measurement of vitamin D blood levels to detect deficiencies that aren't severe enough to produce clinical signs.