But getting that amount from food and sunlight may not be easy, said Robert U. Simpson, a professor of pharmacology at the University of Michigan, whose group was the first to identify vitamin D receptors in heart cells. For example, a glass of fortified milk contains only about 100 IU of vitamin D.
Simpson believes the recommended levels are actually still too low. "People should get at least 1,000 IU, perhaps 2,000," he said. "I take 1,000 IU a day. I recommend that intake right now as part of a multivitamin supplement."
Wang is much more cautious.
"I would still emphasize that studies like ours are not enough to alter practice," he said. Wang said he does not take any vitamin supplement, but he concedes that the recommended 600 IU daily intake for older people is "very, very difficult to achieve," especially in the winter in northern parts of the country.
"Virtually all elderly people have to take supplements," Wang said.
The cardiovascular risk associated with low vitamin D levels was especially great for people who also had high blood pressure. Their incidence of cardiovascular events was double that of people with higher blood levels of vitamin D.
There have been similar studies of other vitamins indicating that they might help prevent heart disease, Wang noted. But efforts at supplementation with those vitamins failed to show a benefit in large-scale, controlled trials, Wang noted.
"The question becomes how much data such as ours is needed to justify a controlled trial," he said. "The answer is, more than we have now."
There's a fact sheet on vitamin D at the U.S. Office of Diet
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