Schernhammer ES et al. – A statistically significant inverse association is observed between melatonin levels measured in overnight morning urine and invasive breast cancer risk in postmenopausal women Methods
Prospective case–control study of the association between melatonin levels and breast cancer risk in 3966 postmenopausal women
Study nested in the Hormones and Diet in the Etiology of Breast Cancer Risk cohort
Measurement of the concentration of melatonin's major metabolite, 6-sulfatoxymelatonin, in baseline 12-hr overnight urine sample from 178 pts who later had incident breast cancer and from 710 matched controls
Results
Increased melatonin levels were associated with a statistically significantly lower risk of invasive breast cancer in postmenopausal pts
Association was strongest among never and past smokers and after excluding pts diagnosed with invasive breast cancer within 4 yrs after urine collection
No substantial variation noted in relative risks by hormone receptor status of breast tumors
Among 3966 women in the cohort, 40 of 992 women in the highest quartile of 6-sulfatoxymelatonin developed breast cancer during follow-up, vs 56 of 992 women in the lowest quartile
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