ThePhysicians' Health Study organised by Charles Hennekens of Harvard University and published in 1989 involved more than 22, 000 healthy American doctors.
Kochar and his colleagues analyzed data on more than 13, 000 men who were part of the long-running Physicians' HealthStudy, which is funded by the National Institutes of Health.
Last month, results of the long-term Physicians' HealthStudy II reported that that neither vitamin E nor vitamin C supplements lower the risk of prostate cancer.