A fairly heavy dose of acetaminophen for five years or longer was associated with an estimated 38 percent lower risk of prostate cancer, U.S. researchers say. Study leader Eric Jacobs, an American Cancer Society epidemiologist, examined the association between acetaminophen use and prostate cancer incidence among 78,485 men in the Cancer Prevention Study II Nutrition Cohort. Data on acetaminophen were obtained from a questionnaire completed at study enrollment in 1992 and updated using follow-up questionnaires in 1997 and every other year thereafter. There were 8,092 incident prostate cancer cases identified from 1992 to 2007. Of this group, current regular use of acetaminophen -- more than 30 pills per month -- for five years or more was associated with lower risk of overall prostate cancer by 38 percent. Regular use of acetaminophen for less than five years duration was not associated with prostate cancer risk. "While the results of this observational study suggest that long-term regular acetaminophen use may be associated with lower prostate cancer risk, our findings require replication by other studies, and do not justify use of acetaminophen to prevent prostate cancer," Jacobs says in a statement. "Acetaminophen is considered relatively safe when used at recommended doses but unintentional acetaminophen overdose is an important cause of acute liver failure. Still, results of this study could lead to further research on acetaminophen that might provide biological insights about the process of prostate cancer development and how this process could be slowed."