The U.S. Food and Drug Administration (FDA) found no proof that the osteoporosis drugs bisphosphonates are linked to atrial fibrillation (AFib), a heart rhythm problem that affects an estimated 2.2 million Americans. The FDAs announcement in November was based on data from studies that included more than 19,000 patients who took bisphosphonates and 18,000 who took placebos for up to three years. The FDA announced that cases of AFib were rare in all the studies and that there was no conclusive proof that bisphosphonates could be linked to the heart problems. The FDAs research followed a study published in the May 3, 2007 issue of the New England Journal of Medicine that found women were at a higher risk of AFib if they took the drug. Likewise, researchers presenting at the 2008 annual meeting of the American College of Chest Physicians analyzed three studies involving more than 16,000 women who either took bisphosphonates or a placebo. About three percent of the women taking the drug experienced AFib-about twice the number who had AFib in the placebo group.