Men with higher levels of the sleep hormone melatonin may be less likely to develop prostate cancer. That’s the finding of research at the Harvard School of Public Health in Boston. It revealed that men who had higher levels of melatonin had a 75 percent decreased risk of advanced prostate cancer compared with men with lower melatonin levels. People’s melatonin levels are affected by the amount of sleep they get, and the quality of that sleep. The hormone is produced in the brain in response to darkness. Men working shifts or with sleep problems had lower levels of melatonin than men with no difficulty sleeping. Study researcher Sarah Markt at The Harvard School of Public Health in Boston says the findings are important because they provide further support for the idea that men’s circadian rhythms influence prostate-cancer development. The American Cancer Society says there’s also evidence that women who work night shifts for many years have lower levels of melatonin and a slightly higher risk of breast cancer.