August 18, 2008

Low Vitamin D Levels Linked to Death Risk

By John Fauber

MILWAUKEE, Wis. - People with low vitamin D levels that are common in Northern Hemisphere locations such as Wisconsin had a significantly higher risk of death than those with healthier levels, a new study has found.

The research, which is believed to be the first study involving vitamin D and mortality risk in the general population, is the latest in a long string of recent reports suggesting that vitamin D might play an important role in preventing a variety of diseases, including cancer and heart disease. However, researchers cautioned that although the study was large, its observational nature does not prove that boosting vitamin D levels prevents disease or premature death.

The study involved 13,331 people in their 40s whose blood was tested for vitamin D levels and who were followed for about nine years. The participants were divided into four groups based on their vitamin D levels.

Those in the bottom quarter, whose vitamin D level was less than 17.8 nanograms per milliliter, had a 26 percent greater risk of dying from any cause than those in the top quarter. Levels below 17.8 ng/ml are not uncommon in places such as Wisconsin, especially in non-summer months.

"I think our lifestyles today make us vitamin D deficient," said lead author Michal Melamed, an assistant professor of medicine and epidemiology at Albert Einstein College of Medicine in New York. "I think physicians will be testing vitamin D more and recommending either supplementation or lifestyle [changes]."

The study, which was funded by the National Institutes of Health, was published this week in the Archives of Internal Medicine.

While there is not unanimous agreement on the optimal level of vitamin D, many doctors say more than 30 ng/mg is desirable.

"Vitamin D deficiency is an epidemic in many parts of the world, including Wisconsin," said Neil Binkley, an associate professor of geriatrics and endocrinology at the University of Wisconsin School of Medicine and Public Health.

He noted that, through much of the evolutionary history of humans, people spent considerably more time outdoors and vitamin D levels of more than 50 ng/mg probably were the norm. Vitamin D is made in the skin when it is exposed to ultraviolet light.

"We were never supposed to eat our vitamin D," he said. "The evolutionary argument is quite profound."

Binkley said the large number of people in the study and its long time span bolstered the study's findings.

However, because the study was observational in nature, the effect of vitamin D on mortality can be only inferred, he said.

Doctors said what are needed are rigorous clinical trials in which vitamin D supplements and placebos are given to a large number of people over many years.

However, because vitamin D is inexpensive, such studies are not likely to be conducted by drug companies, they said.

Nevertheless, over the past few years, there has been a surge in observational studies suggesting a variety of potential health benefits, said Shailesh Patel, chief of endocrinology at the Medical College of Wisconsin and Froedtert Hospital in Wauwatosa.

"There is quite a bit of validity to this study," he said. "This study raises awareness."

Still, it's not yet reasonable to assume that taking vitamin D supplements will be a panacea for preventing diseases such as cancer, heart disease and stroke, he said.

On the other hand, taking 1,000 international units of vitamin D a day, and maybe as much as 2,000 IU, is not likely to cause any harm, he said.

The other question the study did not answer is, if vitamin D does reduce the risk of dying prematurely, how does it do so?

In a preliminary analysis, the authors found a trend toward reduced deaths from cardiovascular disease and cancer, but those numbers did not reach statistical significance.

"It might be that vitamin D affects so many things that we did not have enough people in the study to see an effect [for a specific disease]," said lead author Melamed.

She noted that other research shows that vitamin D can, among other things, lower blood pressure.

Originally published by Milwaukee Journal Sentinel.

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