By Amy Norton
NEW YORK (Reuters Health) - Men who consume the recommended amount of vitamin D are somewhat less likely to suffer a heart attack or stroke than those who get little of the vitamin in their diets, a large U.S. study suggests.
Following nearly 119,000 adults for two decades, researchers found that men who got at least 600 international units (IU) of vitamin D each day -- the current recommended amount -- were 16 percent less likely to develop heart problems or a stroke, versus men who got less than 100 IU per day.
There was no such pattern among women, however, the researchers report in the American Journal of Clinical Nutrition.
The authors say the findings do not prove that vitamin D, itself, deserves the credit for the lower risks seen in men. So they should not start downing supplements for the sake of their hearts.
"The evidence is not strong enough yet to make solid recommendations," said lead researcher Dr. Qi Sun, a research associate at the Harvard School of Public Health.
On the other hand, the apparent benefits were linked to vitamin D intakes near what's already recommended: Last year, the Institute of Medicine (IOM), a scientific advisory panel to the U.S. government, bumped up the recommended dose to 600 IU for most people. Adults older than 70 were told to get 800 IU.
So these latest findings may encourage more people to meet those guidelines, Sun said.
But as far as whether vitamin D cuts heart disease and stroke risk, the jury is still out.
Sun said that more answers should come from an ongoing clinical trial that is looking at whether a high dose of vitamin D (2,000 IU per day) can cut the risk of heart disease, stroke and other chronic diseases.
Clinical trials, wherein people are randomly assigned to a treatment or a placebo, are considered the "gold standard" of medical evidence.
So far, there have been few such randomized clinical trials testing vitamin D's health effects.
A flurry of studies in recent years has linked higher vitamin D intake to lower risks of everything from diabetes, to severe asthma, heart disease, certain cancers and depression.
The problem with those studies is that were "observational" -- researchers looked at people's vitamin D intake, or their blood levels of the vitamin, and whether they developed a given health condition. Those kinds of studies cannot prove cause-and-effect.
The current study was also observational, based on data from two long-term projects that have followed two large groups of U.S. health professionals since the 1980s.
Out of 45,000 men, there were about 5,000 new cases of cardiovascular disease over the study period. These were defined by an incident of heart attack, stroke, or death attributed to cardiovascular disease.
After accounting for a range of factors -- like age, weight, exercise levels and other diet habits, such as fat intake - Sun's team found that men who got at least 600 IU of vitamin D from food and supplements had a 16 percent lower risk of heart attack and stroke compared to men who got less than 100 IU of vitamin D per day.
For women, though, there was no correlation between vitamin D intake and cardiovascular health.
It's not clear why that is, Sun said. One possibility is that women may have less active vitamin D circulating in the blood; vitamin D is stored in fat, and women typically have a higher percentage of body fat than men do.
But more research is needed, Sun said, to know whether real biological differences underlie the current findings.
In theory, vitamin D could help ward off heart disease and stroke; lab research suggests that it may help maintain healthy blood vessel function and blood pressure levels, reduce inflammation in the blood vessels, and aid blood sugar control.
But until clinical trials help show whether vitamin D works, Sun advised people to stick with the tried-and-true ways of protecting their hearts: maintaining a healthy weight, getting regular exercise, eating a well-balanced diet and not smoking.
"There are many established ways to lower your cardiovascular disease risk," Sun said. "People can focus on those measures."
As for vitamin D, the sun is the major natural source, since sunlight triggers vitamin D synthesis in the body. Food sources are relatively few and include fatty fish like salmon and mackerel, and fortified dairy products and cereals.
SOURCE: http://bit.ly/irO9Xe American Journal of Clinical Nutrition, online June 8, 2011.