Objective Limited data exist on the association between menopause and atrial fibrillation (AF). We sought to examine the relationship between menopausal age, postmenopausal hormone therapy (PHT) use and incident AF.

Methods The Women’s Health Study (WHS) enrolled 39 876 female health professionals between 1992 and 1995. We prospectively examined 30 034 women in WHS using Cox proportional-hazard models. Participants were free of cardiovascular disease and AF at baseline and had not undergone hysterectomy without bilateral oophorectomy prior to menopause. Incident AF was confirmed by medical record review.

Results At baseline, median age was 53 years (IQR 49–60), median menopausal age was 50 years (IQR 46–52) and 14 415 (48.0%) had prior PHT use. Over a median follow-up of 20.5 years, 1350 AF events occurred. In multivariable analysis, relative hazards for AF were lower among women with younger age at menopause but did not differ significantly from women with the oldest menopausal age (<45: HR 0.82, 95% CI 0.67 to 1.02; 45–49: HR 0.90, 95% CI 0.74 to 1.08; 50–54: HR 0.89, 95% CI 0.75 to 1.06; >54 years: referent). Use of oestrogen-alone PHT, but not oestrogen and progesterone, was independently associated with AF risk (HR 1.22; 95% CI 1.02 to 1.45 vs HR 1.04; 95% CI 0.86 to 1.26). This relationship was not attenuated by intermediary cardiovascular events.

Conclusions In this large prospective study, menopausal age was not significantly related to incident AF, while use of oestrogen monotherapy was associated with increased AF risk. Our findings suggest a pathophysiological link between unopposed oestrogen exposure and AF in women.

Clinical trial registration NCT000000479; Post-results.