Birth cohort effects on diagnosed atrial fibrillation incidence: nationwide cohort study from 1980 to 2018

Background The incidence of atrial fibrillation (AF) shows substantial temporal trends, but the contribution of birth cohort effects is unknown. These effects refer to the relationship between birth year and the likelihood of developing AF. We aimed to assess trends in cumulative incidence of diagnosed AF across birth cohorts and to disentangle the effects of age, birth cohort and calendar period by using age–period–cohort analyses. Methods In a Danish nationwide population-based cohort study, 4.7 million individuals were selected at a given index age (45, 55, 65 and 75 years) free of AF and followed up for diagnosed AF. For each index age, we assessed trends in 10-year cumulative incidence of AF across six 5-year birth cohorts. An age–period–cohort model was estimated using Poisson regression with constrained spline functions collapsing data into 1-year intervals across ages and calendar years. Results Cumulative incidence of AF diagnosis increased across birth cohorts for all index ages (p trend <0.001). Compared with the first birth cohort, the diagnosed AF incidence rate ratio in the last birth cohort was 3.0 (95% CI 2.9 to 3.2) for index age 45 years, 2.9 (2.8 to 3.0) for 55 years, 2.8 (2.7 to 2.8) for 65 years and 2.7 (2.6 to 2.7) for 75 years. Age–period–cohort analyses showed substantial birth cohort effects independent of age, with no clear period effect. Compared with individuals born in 1930, the diagnosed AF incidence rate was 0.125 smaller among individuals born in 1885 and was four times larger among individuals born in 1975. Conclusion Substantial birth cohort effects, independent of age and calendar period, influence trends in diagnosed AF incidence.