Breast cancer mortality and the change in fertility risk factors at menopause: a prospective study of 800,000 married Norwegian women.
I examined breast cancer mortality in relation to fertility factors in a cohort of 800,814 married Norwegian women aged 25-74 years at the start of follow-up. Women aged 25-44 years with a first birth after the age of 35 years had a RR = 2.58 compared with women with a first birth before the age of 20 years. For women aged 45-74 years, the corresponding RR was 1.35. On the other hand, the rate differences between women with a late first birth (35+ years) and an early birth (less than 20 years) were similar for women of different ages. Small rate differences were found for premenopausal women between uniparous women and women with 6-7 children, but postmenopausal women with many children had lower rates of breast cancer mortality than uniparous women. For postmenopausal women the rate differences were stable over age categories. This study points toward a change in fertility risk factors at menopause.
Lund
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Institute of Community Medicine, University of Tromsø, Norway.
D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000401:mortality*; D015331:Cohort Studies; D005260:Female; D005298:Fertility; D005500:Follow-Up Studies; D006801:Humans; D008423:Maternal Age; D008593:Menopause; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D010298:Parity; D016012:Poisson Distribution; D011247:Pregnancy; D011446:Prospective Studies; D012307:Risk Factors