When it comes to the heart, vitamin D can be a double-edged sword.
Scientists have long known that low levels of the nutrient can hurt the heart, but new research shows that higher than normal levels can make it beat too fast and out of rhythm, a condition called atrial fibrillation, according to a report presented at the annual meeting of the American Heart Association.
The study, which followed 132,000 patients at a Utah based medical center, found that the risk of newly developed atrial fibrillation jumped almost three-fold when blood levels of vitamin D were high.
Most people get at least some of their daily needs of vitamin D from sunlight. But in cold northern climates where everyone bundles up for the winter -- inadvertently blocking rays that raise the body’s vitamin D levels -- people are often encouraged to take supplements to boost levels of the nutrient to protect the bones and heart, said the study’s lead author, Dr. Jared Bunch, director of electrophysiology research at the Intermountain Medical Center in Murray, Utah.
However, because everyone absorbs these supplements differently, blood levels need to be tested to make sure they’re in the safe range, Bunch explained.
High levels of vitamin D only occur when people take supplements, Bunch said. Because consumers assume supplements sold over the counter are safe, they may not realize the danger of taking too much vitamin D, he added.
“People are looking toward therapies considered to be natural to treat a broad variety of disease states and as a means of prevention,” Bunch said. “We see patients who take a tremendous amount of vitamin supplements.”
Bunch said the normal range for vitamin D was 41 to 80 nanograms per deciliter (ng/dl). Patients in the study were designated as having excessive vitamin D had had readings above 100 ng/dl.
The recommended daily intake of vitamin D for people from 1 year to age 70 is 600 IUs, or international units a day, based on what is sufficient for bone health, according to the National Institutes of Health. There are few natural food sources of vitamin D, although oily fish such as tuna or salmon are among the best. For example, 3 ounces of cooked salmon contains 447 IUs of vitamin D per serving. Small amounts are also found in cheese and egg yolks. The Department of Agriculture provides a comprehensive list of foods containing vitamin D.
Bunch advised people who have recently been diagnosed with atrial fibrillation and are taking vitamin D supplements to make sure their doctors check blood levels of the nutrient.
He suspects that the effects of high vitamin D on heart rhythms are reversible.
“If the levels are excessive, I would hope that when they’re cut back the arrhythmias would improve as well,” Bunch said.
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