People with excess levels of vitamin D have a higher risk of the heart condition atrial fibrillation, U.S. researchers say. Lead investigator Dr. T. Jared Bunch, a heart rhythm specialist at the Intermountain Medical Center Heart Institute in Utah, said the findings are significant because so many Americans use vitamin supplements to promote their health. Researchers at Intermountain Medical Center studied more than 132,000 patients and found the risk of developing atrial fibrillation was two and a half times greater in those with excess levels of vitamin D compared to patients with normal levels. \"There are both benefits and harm to taking vitamin supplements of all kinds,\" Bunch said in a statement. \"Our goal is to determine a safe dose and usage range so patients can understand what amount is healthy, and what amount may be toxic.\" The Institute of Medicine currently advises healthy adults should be able to take as much as 4,000 International Units of vitamin D daily, but in reality doctors don\'t yet know how much vitamin D causes toxicity, Bunch said. The findings were reported at the American Heart Association Scientific Sessions in Orlando, Fla.