Vitamin D is good for your bones, doctors have said for years, but new research suggests that taking a vitamin pill a day might extend your life.
The findings, published yesterday in the journal Archives of Internal Medicine, add to the growing medical literature about the benefits of what is sometimes called the "sunshine vitamin" because it is produced by the skin in response to sunlight. Recent studies have linked vitamin D deficiencies to higher risk of cancer, diabetes and multiple sclerosis. It could play a role in reducing heart disease and preventing pre-eclampsia in pregnant women.
"It's very new to see [the effects of] vitamin D on organs different than the bones," said Dr. Philippe Autier, a co-author of the study. "These are very ordinary doses. You don't need four or five pills a day. ...
"You should probably get rid of all the other" vitamins in the medicine cabinet, Autier said by phone from Lyon, France, where he is a researcher at the International Agency for Research on Cancer. "At this point, that's where we are. This is quite real."
Consumers are getting used to being told about new benefits of vitamins.
Yesterday, a team led by Johns Hopkins scientists reported that vitamin C inhibits the growth of some tumors in mice. In recent years, vitamin E, beta-carotene and other antioxidants were praised as having miracle properties but when more research was done, they lost some of their luster. One trial last year showed that patients with neck cancer who received large doses of vitamins C, E and beta carotene experienced fewer side effects of cancer treatments, but in the end they died at twice the rate of those who didn't get vitamins.
Past experience means there "is some need to be cautious" about vitamins, said Edgar Miller, associate professor of medicine at Johns Hopkins and an antioxidant researcher:
"I think there is enough evidence to recommend vitamin D supplements in most women, certainly who are older and have dietary deficiencies. How high a dose? We don't know. Is there a threshold of benefit beyond which there's harm? That's something that needs to be studied."
Still, he said, "everything seems to be lining up very well with vitamin D."
Autier's analysis looked at 18 trials involving vitamin D supplements that included more than 57,000 patients and evaluated doses ranging from 300 international units to 2,000 international units. Most commercially available supplements contain 400 to 600 IU. Over an average of nearly six years, those who took vitamin D had a 7 percent lower risk of death from all causes than those who did not.
Some scientists say more years of study would give better clues as to how large a role vitamin D plays in decreasing mortality. Others point out that while there was a statistically significant 7 percent drop in mortality in Autier's analysis, because of the size of the study that only accounted for a difference of 117 people who died in the control groups as compared with those who took vitamin D supplements.
Some vitamin D researchers believe that as people have spent more and more time indoors, as opposed to the long stretches spent outdoors and uncovered in agrarian times, they have developed serious vitamin D deficiencies. They say levels that are considered normal in the United States are one-fifth of the levels of 10,000 years ago.
Dr. Cedric F. Garland, a cancer prevention specialist at the University of California, San Diego, said some cancers - rare in agrarian times - can be blamed on vitamin D deficiencies, something researchers have just begun to understand in the past few years.
"We just never realized the deficiency was there," he said.
Garland said the link between the sunshine vitamin and cancers can be seen in new data released by the United Nations, which show cancer incidence rates in 177 countries in the world. As you move farther from the Equator, cancer levels rise, he said.
"Sunny latitudes have markedly lower incidences of cancer of the colon, breast, ovary," he said. "It's such a powerful association with both hemispheres. It leaves no other logical explanation."
The most severe vitamin D deficiencies are associated with rickets, a disease that weakens the bones, though it is not common as it was before scientific advances were made in the early 20th century. In 1922, a Johns Hopkins researcher isolated the rickets-fighting compound in cod liver oil, a fairly new treatment at the time, and labeled it vitamin D.
Getting enough vitamin D isn't easy. About 10 minutes in the sun during peak hours - hold the sunscreen - should be more than enough to produce the currently recommended level. But many fear the sun's harmful rays or are stuck behind desks during the heat of the day. African-Americans might need even more exposure, as the pigmentation in their skin makes it harder to process sunlight into vitamin D and leaves them more vulnerable to deficiencies.
Fish, liver and egg yolk are the only foods that naturally contain vitamin D, though some other foods are fortified with it. Still, to get 800 IU of vitamin D from fortified milk you would have to drink two quarts a day.
"It's impossible to get enough in your diet," said Dr. Elizabeth Streeten, an assistant professor at the University of Maryland School of Medicine who runs the metabolic bone disease program there.
She has long been telling her patients to take 1,000 IU or more daily. And her relatives, too.
Alongside their other gifts, she said. "I've been trying to give bottles of vitamin D to my family for holidays for years."
There is little evidence of vitamin D toxicity at levels under 10,000 IU a day, several said. The upper limit recommended by the National Academy of Sciences is 2,000 IU, and Garland said there might be a push to extend that to 4,000 IU. He expects to see even more good news because the research "is rapidly accelerating."
"It seems like each month or two there's something new that's found," he said.
Dr. Joan Lappe is an osteoporosis researcher at Creighton University in Omaha, Neb. She is studying the effects in 1,200 rural postmenopausal women of calcium and calcium plus vitamin D supplements on osteoporosis-related fractures. In a study published this summer, she and her colleagues found that after four years, those who took calcium and vitamin D had a 60 percent lower risk of developing cancer, compared with the placebo group. The calcium-only group had a 47 percent reduced risk.
Most studies have been done in older women, often unhealthy women. Lappe said she wants to see further studies - in men, in younger people - but right now, she thinks the "data strongly suggest vitamin D [is helpful] in preventing cancer."
"It's such a simple thing," she said. "Imagine taking a vitamin to prevent cancer. It's almost too good to be true."
Aids in the absorption of calcium, helping to form and maintain strong bones.
Might provide protection from osteoporosis, hypertension, cancer and several autoimmune diseases.
In sufficient doses, might increase life expectancy.