Menstrual cycle characteristics and history of ovulatory infertility in relation to breast cancer risk in a large cohort of US women.
Menstrual cycle characteristics and ovulatory infertility were evaluated in relation to breast cancer risk among 116,678 women in the Nurses' Health Study II, a prospective cohort study of female registered nurses who were aged 25-42 years and living in 14 US states at enrollment in 1989. During 396,299 person-years of follow-up between return of the baseline questionnaire and June 1993, 251 cases of breast cancer were identified in this cohort. The multivariate relative risk (RR) associated with age at menarche > 13 years compared with age < or = 12 years was 0.66 (95% confidence interval (CI) 0.44-0.99). Short and long menstrual cycle lengths at ages 18-22 years were associated with reduced risk. Compared with menstrual cycle length 26-31 days, the multivariate relative risks (95% CIs) for more extreme cycle lengths were: < 26 days, 0.50 (0.25-0.98); 32-39 days, 0.81 (0.51-1.28); and > 39 days or too irregular for estimation of a usual cycle length, 0.41 (0.18-0.94). The multivariate relative risk associated with a history of ovulatory infertility, compared with no such history, was 0.41 (95% CI 0.18-0.93). These results are consistent with the hypothesis that reduced exposure to ovulatory menstrual cycles provides a protective effect against breast cancer.
Garland
M
M
Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA.
Hunter
D J
DJ
Colditz
G A
GA
Manson
J E
JE
Stampfer
M J
MJ
Spiegelman
D
D
Speizer
F
F
Willett
W C
WC
D000328:Adult; D001943:Breast Neoplasms / Q000209:etiology*; D005260:Female; D006801:Humans; D007247:Infertility, Female / Q000150:complications*; D008572:Menarche; D008597:Menstrual Cycle; D015999:Multivariate Analysis; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014481:United States