The largest study of its kind concludes that long-term multivitamin use has no impact on the risk of common cancers, cardiovascular disease or overall mortality in postmenopausal women. The results of the Women's Health Initiative study, led by researchers at Fred Hutchinson Cancer Research Center, were published in the Feb. 9 issue of the Archives of Internal Medicine.

"Dietary supplements are used by more than half of all Americans, who spend more than $20 billion on these products each year. However, scientific data are lacking on the long-term health benefits of supplements," said lead author Marian L. Neuhouser, Ph.D., an associate member of the Public Health Sciences Division at the Hutchinson Center.

The study focused the effects of multivitamins because they are the most commonly used supplement. "To our surprise, we found that multivitamins did not lower the risk of the most common cancers and also had no impact on heart disease," she said.

The study assessed multivitamin use among nearly 162,000 women enrolled in the Women's Health Initiative, one of the largest U.S. prevention studies of its kind designed to address the most common causes of death, disability and impaired quality of life in postmenopausal women. The women were followed for about eight years.

Nearly half of the study participants - 41.5 percent - reported using multivitamins on a regular basis…