A prospective study of reproductive factors in relation to risk of systemic lupus erythematosus among black women

Objective Systemic lupus erythematosus (SLE) occurs most commonly among reproductive age women, compatible with a potential role of reproductive factors, although past studies including women of mainly European ancestry have yielded conflicting results. We assessed relationships of reproductive factors to SLE risk among black women. Methods We followed 58,243 participants in the Black Women’s Health Study (BWHS) from 1995 – 2015 using biennial health questionnaires, on which participants reported reproductive and other factors. Self-reported incident SLE cases were confirmed as meeting 1997 American College of Rheumatology SLE classification criteria by medical record review. Cox proportional hazards regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (95% CI) for SLE for several reproductive factors, controlling for potential confounders. Results During 954,476 person-years of follow-up, 125 incident cases of SLE were confirmed. Later age at menarche and longer duration of breast feeding were associated with increased risk of SLE. The multivariable HRs were 2.31 (95% CI, 1.30–4.11) for age at menarche ≥15 relative to age 12, and 1.73 (95% CI, 1.01–2.94) for breast feeding ≥6 months relative to none. There were no clear associations with parity, age at first birth, menopausal status, hysterectomy, age at menopause, or history of endometriosis. Conclusion Our results suggest that later menarchal age and breastfeeding of infants for ≥6 months vs. none may be associated with increased SLE risk among black women, while other reproductive factors did not appear related. The biological mechanisms underlying these potential associations should be pursued.