A large body size in early adult life has been associated with an increased risk of atrial fibrillation (AF) later in life in men; however, this has not yet been investigated in women. Design: Prospective cohort study. Methods: We included all women in the Swedish Medical Birth Registry with known weight and height from 1982 to 2014. The main exposure body surface area (BSA) was calculated as the square root of (height [cm] × weight [kg]/3600). Information on hospital diagnoses of AF were obtained from the Patient Registry. The study population comprised 1,522,329 women (mean age 28.3 years). Results: A total of 6993 women (0.5%) were diagnosed with AF during a maximum follow-up of 33.6 years (mean 16.6 years, confidence interval [CI] 16.6–16.6). Risk of AF rose linearly with increasing BSA, body mass index (BMI) and height, with up to a threefold increased risk in the biggest women. Hazard ratios associated with BSA were 1.21 (95% CI 1.12–1.30), 1.45 (95% CI 1.35–1.56) and 2.11 (95% CI 1.97–2.26) when comparing the second, third and fourth quartiles, respectively, with the first. The elevated risk persisted after stratifying for different levels of BMI, even among women with low-normal BMI.Conclusion
A larger body size measured early in adulthood was, independent from BMI, associated with an increased risk of AF in women during follow-up of up to 33 years.