A new study published in the Journal of the National Cancer Institute has found that higher levels of a melatonin metabolite are associated with a lower risk of breast cancer.

The production of melatonin - a hormone that the body produces only during the dark phase of the light-dark cycle - is suppressed by exposure to light during the night. Studies of night-shift workers have found an association between night-shift work (a surrogate for light exposure at night) and an increased risk of breast cancer, but the association between melatonin levels and breast cancer risk has been uncertain.

To examine the association between urinary melatonin levels and breast cancer risk, Eva S. Schernhammer, M.D., Dr.P.H., and Susan E. Hankinson, Sc.D., of Brigham and Women's Hospital and Harvard Medical School in Boston, conducted a prospective case-control study nested within the Nurses' Health Study II cohort. They measured levels of a major melatonin metabolite in the urine of 147 women with invasive breast cancer and 291 matched control women.

Women in the highest quartile of melatonin metabolite levels had a 40% lower risk of invasive breast cancer compared with those in the lowest quartile. The authors conclude that their data supports the hypothesis that higher melatonin levels are associated with a lower risk of breast cancer.

SOURCE:
Journal of the National Cancer Institute, July 20, 2005