BREAST-FEEDING, OTHER REPRODUCTIVE FACTORS AND RHEUMATOID-ARTHRITIS -A PROSPECTIVE-STUDY

The evidence regarding reproductive events as risk factors for rheumat oid arthritis (RA) is not conclusive. In the present study a populatio n-based cohort consisting of 63 090 women were followed from 1961 to 1 989. Detailed data on reproductive factors were collected through pers onal interviews in the period 1956-9. The endpoint used was mention of RA on the death certificate. Mortality rate ratios were estimated by Poisson regression, controlling for various demographic variables. Dur ing 1 485 400 person-yr of observation, a total of 355 cases with RA m entioned on the death certificate were identified. Total time of lacta tion was associated with a decreased mortality of RA, with an approxim ate dose-response relationship. The results did not support a role of parity, age at first and last birth, or age at menarche and menopause in the development of RA. This protective effect of lactation on the d evelopment of RA has not previously been described, and since a defini te biological explanation is lacking, the association should be confir med in other populations.