HEALTH NEWS

Study Title:

Melatonin and Breast Cancer

Study Abstract

Background Low urinary melatonin levels have been associated with an increased risk of breast cancer in premenopausal women. However, the association between melatonin levels and breast cancer risk in postmenopausal women remains unclear. Methods We investigated the association between melatonin levels and breast cancer risk in postmenopausal women in a prospective case-control study nested in the Hormones and Diet in the Etiology of Breast Cancer Risk cohort, which included 3966 eligible postmenopausal women. The concentration of melatonin's major metabolite, 6-sulfatoxymelatonin, was measured in a baseline 12-hour overnight urine sample from 178 women who later developed incident breast cancer and from 710 matched control subjects. We used multivariable-adjusted conditional logistic regression models to investigate associations. Relative risks are reported as odds ratios (ORs). All statistical tests were two-sided. Results Increased melatonin levels were associated with a statistically significantly lower risk of invasive breast cancer in postmenopausal women (for women in the highest quartile of total overnight 6-sulfatoxymelatonin output vs the lowest quartile, multivariable OR also adjusted for testosterone = 0.56, 95% confidence interval [CI] = 0.33 to 0.97; P(trend) = .02). This association was strongest among never and past smokers (OR = 0.38, 95% CI = 0.20 to 0.74; P(trend) = .001) and after excluding women who were diagnosed with invasive breast cancer within 4 years after urine collection (OR = 0.34, 95% CI = 0.15 to 0.75; P(trend) = .002). We did not observe substantial variation in relative risks by hormone receptor status of breast tumors. Among the 3966 women in the cohort, 40 of the 992 women in the highest quartile of 6-sulfatoxymelatonin developed breast cancer during follow-up, compared with 56 of the 992 women in the lowest quartile of 6-sulfatoxymelatonin. Conclusion Results from this prospective study provide evidence for a statistically significant inverse association between melatonin levels, as measured in overnight morning urine, and invasive breast cancer risk in postmenopausal women.

Press Release:

Low melatonin levels are associated with an increased risk of breast cancer in postmenopausal women, according to a prospective case-control study.

Melatonin is primarily secreted during the dark hours of a light-dark cycle and has been shown to be low in some night workers. Researchers have found that low melatonin levels in premenopausal women are associated with an increased risk of breast cancer.

To find out if a similar association occurs in postmenopausal women, Eva Schernhammer, M.D., Dr.P.H., of the Brigham and Women's Hospital and Harvard Medical School in Boston and colleagues compared melatonin levels in 178 postmenopausal women and 710 matched controls. All of the women were enrolled in the prospective Hormones and Diet in the Etiology of Breast Cancer Risk study.

The researchers found that women with the lowest levels of melatonin had a statistically significantly higher incidence of breast cancer than those with the highest levels.

The researchers conclude that low melatonin levels are associated with an increased risk of breast cancer. Further studies need to confirm these data and should investigate the mechanisms that underlie the association.

Study Information

Schernhammer ES, Berrino F, Krogh V, Secreto G, Micheli A, Venturelli E, Sieri S, Sempos CT, Cavalleri A, Schünemann HJ, Strano S, Muti P.
Urinary 6-Sulfatoxymelatonin Levels and Risk of Breast Cancer in Postmenopausal Women.
J Natl Cancer Inst.
2008 June
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA (ESS),