Reduced breast cancer mortality among fishermen's wives in Norway.

International comparisons show that populations having a high consumption of fish experience low incidence of breast cancer. We compared death rates from breast cancer among socioeconomic groups in a prospective study of 533,276 Norwegian women aged 35-54 years who were followed from 1970 through 1985. Compared with the reference group (wives of unskilled workers) the fishermen's wives had a decreased risk of breast cancer with a relative risk (RR) of 0.67 (95% confidence interval [CI] = 0.47-0.94) adjusted for age and the number of children. Among fishermen's wives who were parous, adjustment for age at first birth gave an RR of 0.62 (CI = 0.43-0.91). This study supports the hypothesis that certain aspects of diet, i.e., fish consumption, may be associated with lower breast-cancer mortality.