Vitamin D Might Reduce Risk of Cardiovascular Disease

Doctors are learning more about an important nutrient our bodies need in order to function optimally: vitamin D, which helps the body absorb calcium.

Research has indicated that vitamin D could provide protection from conditions such as osteoporosis, hypertension, cancer, infections, and some autoimmune disorders. And many of us - especially those who live in areas without much sunshine - don't get enough of it.

The authors of a study published in January 2008 in Circulation: Journal of the American Heart Association (Circulation. 2008;117:503-511) suggested that a deficiency of vitamin D may have an adverse effect on the cardiovascular system. That study caught the attention of Denise Teves, MD, Medical College of Wisconsin Assistant Professor of Medicine, whose practice focuses on Endocrinology, Metabolism and Clinical Nutrition.

"Until recently, we weren't fully aware of the relationship between vitamin D and heart disease," Dr. Teves said. "I'm happy we have this information, although we'll need a larger, more rigorous study to make final conclusions. Some cardiologists are still cautious about interpreting the results, but it certainly has raised eyebrows in the health community."

The study, part of the large, multi-year Framingham Heart Study, followed 1,739 healthy Caucasian men and women for more than five years. At the end of the study, the researchers found that those who were deficient in vitamin D - especially those who also had high blood pressure - had a higher incidence of heart disease.

The Framingham researchers noted that, although evidence suggests that low levels of vitamin D might adversely affect the cardiovascular system, it hasn't yet been proven that a deficiency actually increases the risk of cardiovascular disease.

Vitamin D and Heart Function
How does vitamin D affect heart function? There are several possible ways, Dr. Teves says. Perhaps due to anti-inflammatory properties, vitamin D might decrease the thickening of heart tissue that can lead to heart failure. Vitamin D can also balance the hormonal pathway that regulates blood pressure, and may reduce calcification in the cardiovascular system."

It is fairly well-established, Dr. Teves said, that a lack of vitamin D contributes to osteoporosis - a condition she sees frequently in her patients, many of whom are deficient or insufficient in vitamin D. After reading the Circulation study, she plans to develop a proposal to study vitamin D levels among patients with kidney failure.

How much vitamin D should we get daily? Much more than the current recommended daily requirement of 400 units, the amount commonly found in multivitamins, Dr. Teves says: "I would think people should consume at least twice that much - 800 units per day - and possibly as much as 2,000 units a day."

But it's important that patients discuss any supplementation with their physicians, Dr. Teves notes. Because it is a fat-soluble (rather than water-soluble) vitamin, vitamin D can build up in the body and potentially become toxic, resulting in symptoms including nausea, vomiting, poor appetite, constipation, weakness, and weight loss.

According to the Office of Dietary Supplements (ODS), high levels of vitamin D can also raise blood levels of calcium, causing heart rhythm abnormalities and mental status changes such as confusion.

Sources of Vitamin D
Sunlight is perhaps the most important source of vitamin D. Unfortunately, for those of us who live far from the equator, it's highly likely we're not getting enough vitamin D because we have limited sun exposure year-round. The Circulation study estimated that one-third to one-half of otherwise healthy older adults in the United States have low levels of vitamin D.

Only a few commonly consumed foods are good sources of vitamin D, according to the Office of Dietary Supplements. Most milk in the United States is fortified with vitamin D, and it's added to some cereals and orange juice. The richest food sources are cod liver oil, cooked fish such as salmon and mackerel, and tuna and sardines that are canned in oil.

"It can be difficult to get enough vitamin D from diet alone," Dr. Teves says, "so it's usually necessary to add vitamin D supplements, especially in winter." The Office of Dietary Supplements indicates that adults 50 and older require higher levels of vitamin D than do younger people.

"Vitamin D exerts a range of effects on bones and muscles," Dr. Teves said. "Researchers are studying the role of vitamin D in improving the response to infections and recurrence of cancer, and now, the possibility that it helps maintain a healthy heart."

Barbara Abel
HealthLink Contributing Writer

Dr. Teves practices at both the Froedtert & Medical College Endocrinology, Metabolism and Clinical Nutrition Clinic and the Zablocki VA Medical Center.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.