It is the latest evidence that taking too many vitamins may be harmful. Last month, a study linked heavy vitamin use to fatal prostate cancer, and other research has shown beta-carotene pills can heighten smokers' risk of lung cancer.

The results surprised scientists. Previous studies showed diets low in folic acid led to a higher risk of colon cancer.

The new findings, appearing in today's Journal of the American Medical Association, are based on data from 987 adults with a history of precancerous colon polyps. Several years later, those who took folic acid developed more growths, or adenomas, than the people who took dummy pills.

Folic acid is an artificial version of folate, a B vitamin found in leafy vegetables, citrus fruit and beans. It prevents birth defects and is needed for the production of red blood cells.

From the June 18, 2007, Prepared Foods e-Flash