PARITY IN RELATION TO MORTALITY AND CANCER INCIDENCE - A PROSPECTIVE-STUDY OF NORWEGIAN WOMEN

Background. Few prospective studies relating childbearing to total and cause-specific mortality and cancer incidence have been published. Th e purpose of this paper was to examine these relations in a large coho rt of Norwegian women. Methods. Information on reproductive factors wa s obtained through interviews with 63 090 women. All deaths and cancer cases during follow-up, 1961-1980, were obtained by linkage to the fi les at the Central Bureau of Statistics and the Cancer Registry of Nor way, respectively. Associations with parity were assessed by stratifie d logistic regression. Results. For cerebrovascular and ischaemic hear t disease, moderate but highly significant positive trends of increasi ng mortality with increasing parity were observed in the older part of the cohort. Deaths from diseases of ?he respiratory system and suicid e were most common among nulliparous women. Inverse associations with parity were observed for cancers of the breast, corpus uteri and ovari es as well as for melanoma and non-melanoma skin cancers. Positive ass ociations were observed for cancer of the cervix uteri in all age grou ps, for cancer of the respiratory system among older women and for pan creatic cancer and multiple myelomas in the younger part of the cohort . The results gave no support to previous reports of positive associat ions with cancer of the liver or gallbladder. Conclusions. The study s upports evidence of an increased risk of ischaemic heart disease in mu ltiparous women, which had been observed previously in three smaller p rospective studies. It confirms earlier observations of low risks of c ancer of the breast, corpus uteri and ovaries in women with high parit y.