After a series of conflicting reports about whether vitamin pills can stave off chronic disease, researchers announced on Wednesday that a large clinical trial of nearly 15,000 older male doctors followed for more than a decade found that those taking a daily multivitamin experienced 8 percent fewer cancers than the subjects taking dummy pills.

While many studies have focused on the effects of high doses of particular vitamins or minerals, like calcium and vitamin D, this clinical trial examined whether a common daily multivitamin had an effect on overall cancer risk. A randomized, double-blinded clinical trial, the kind considered the most rigorous type of study, it was one of the largest and longest efforts to address questions about vitamin use.

The findings were to be presented Wednesday at an American Association for Cancer Research conference on cancer prevention in Anaheim, Calif., and the paper was published online in The Journal of the American Medical Association.

The reduction in total cancers was small but statistically significant, said the study’s lead author, Dr. J. Michael Gaziano, a cardiologist at Brigham and Women’s Hospital and the VA Boston Healthcare System. While the main reason to take a multivitamin is to prevent nutritional deficiencies, Dr. Gaziano said, “it certainly appears there is a modest reduction in the risk of cancer from a typical multivitamin.”