It's no coincidence that people who live closer to the equator suffer less incidents of heart attacks and strokes. Adequate vitamin D, which is absorbed primarily through exposure to sunlight, helps prevent such diseases, new research finds.
"There are a whole array of studies linking increased cardiovascular risk with vitamin D deficiency," noted Dr. James H. O'Keefe, director of preventive cardiology at the Mid America Heart Institute in Kansas City. "It is associated with major risk factors such as high blood pressure, diabetes and stiffening of the left ventricle of the heart and blood vessels. Inflammation is really important for heart disease, and people with vitamin D deficiency have increased inflammation."
O'Keefe is the lead author of a review of such studies to be published in the Dec. 9 issue of the Journal of the American College of Cardiology. Experts estimate that up to half of adults and 30 percent of children and teenagers in the United States are vitamin D-deficient, according to the report.
Recent data from the long-running Framingham Heart Study indicated that someone with vitamin D levels below 15 nanograms per milliliter of blood is twice as likely to suffer a heart attack, stroke or other cardiovascular problem within two years as someone with the recommended 20 nanograms per milliliter, the report said.
Vitamin D is well known as the "sunshine vitamin" because human skin makes the nutrient upon exposure to sunlight. Only 10 minutes of exposure to sunlight between 10 a.m. and 3 p.m. each day will be enough for whites to reach the recommended level, experts say. People with darker skins will need somewhat longer exposure. Sunscreen can also block vitamin D production, the experts add.
People must balance the risks and benefits of sun exposure, however. "A little bit of sunshine is a good thing, but the use of sunscreen to guard against skin cancer is important if you have more than 15 to 30 minutes of intense sunlight exposure," O'Keefe noted.
Some foods are also rich in vitamin D, he noted. "Salmon and other deepwater fish are good," O'Keefe said. "Also milk, which is supplemented with vitamin D. But you would have to drink 10 to 20 glasses of milk a day to get the recommended intake."
Recommended vitamin D intake is 200 international units a day up to age 50, 400 units for ages 50 to 70, and 600 units a day over the age of 70.
One way to reach that level is to pop a supplement, O'Keefe said. "There is strong evidence that supplementing vitamin D improves health."
"This is an important report," 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. "It will help those interested in cardiovascular disease understand more about the vitamin D system."
Vitamin D is not just another vitamin, Simpson said. "It is a precursor to a hormone, and this prehormone is responsible for making a very important regulator of cardiovascular processes," he said.
Supplementation is an acceptable way of getting enough vitamin D, Simpson added. "Food is not really an option," Simpson said. "You don't get enough vitamin D in the foods we ordinarily eat. Supplementation is my preferred choice, although I get sunlight whenever the sun shines here in Ann Arbor."