Reproductive and menopausal factors and risk of systemic lupus erythematosus in women.

OBJECTIVE: Systemic lupus erythematosus (SLE) occurs predominantly in women, and hormones may play a role in its etiology. This study was carried out to examine associations between female reproductive and menopausal factors and the development of SLE.
METHODS: A cohort of 238,308 women was prospectively examined. Subjects were older women (ages 30-55 years at start) and younger women (ages 25-42 years at start) from the Nurses' Health Study (NHS) and NHSII cohorts. Incident SLE diagnosed between 1976 and 2003 was confirmed by medical record review. The relative risk (RR) of SLE was estimated separately in each cohort using Cox proportional hazards models, and then pooled using meta-analysis random effects models.
RESULTS: Two hundred sixty-two incident cases of SLE were confirmed among the women. In multivariable models adjusted for reproductive and other risk factors, age<or=10 years at menarche (pooled RR 2.1, 95% confidence interval [95% CI] 1.4-3.2), oral contraceptive use (pooled RR 1.5, 95% CI 1.1-2.1), and use of postmenopausal hormones (RR 1.9, 95% CI 1.2-3.1) significantly increased the risk of SLE. An elevation of SLE risk was observed among postmenopausal women primarily after surgical menopause (RR 2.3, 95% CI 1.2-4.5), and also among women with earlier age at natural menopause (P for trend<0.05). Menstrual irregularity was associated with an increased risk of SLE among women in the younger (NHSII) cohort. Age at first birth, parity, and total duration of breastfeeding were not associated with SLE.
CONCLUSION: Early age at menarche, oral contraceptive use, early age at menopause, surgical menopause, and postmenopausal use of hormones were each associated with an increased risk of SLE. These associations may point to the mechanisms underlying the pathogenesis of SLE.