A high level of cardiorespiratory fitness (CRF) among adolescents was associated with a small excess risk of atrial fibrillation (AFib) during early adulthood – but this was outweighed by larger reductions in non-AFib cardiovascular disease later in life and after controlling for familial cofounders, according to research published May 21 in Circulation.
The cohort study followed 1,124,049 Swedish young adult men for up to 50 years, from 1972-1995 to 2023. CRF was assessed with a maximal ergonomic bicycle test during Sweden’s mandatory military conscription exam (mean age at test, 18.3 years).
Compared with lower deciles of adolescent CRF, men in higher deciles were born later, had a higher BMI and had parents with a higher level of education and income.
Results showed that 45,179 men (4.0%) experienced a first AFib event at a median age of 54.8 years, and 96,404 men (8.6%) experienced a first non-AFib cardiovascular event at a median age of 54.4 years.
Furthermore, better CRF in adolescence was associated with higher risk of AFib and lower risk of non-AFib cardiovascular disease – with a switch by the age of 45 to greater non-AFib risk reduction, which became more pronounced with age.
Within a sub-cohort of 477,453 full siblings from 219,304 families, when controlling for all behavioral, environmental and genetic factors, the excess AFib risk was outweighed by non-AFib benefit at all ages. By age 35, reduction in non-AFib cardiovascular disease was substantially larger (risk difference [RD], –0.11%) than excess risk in AFib (RD, 0.06%), and by 65 years, the gap widened further (RD, –3.91% vs. RD, 2.30%).
“Although current guidelines such as those from the European Society of Cardiology and the American College of Cardiology/American Heart Association emphasize the benefits of exercise and CRF in relation to [AFib] risk, uncertainties remain concerning the role of high intensity exercise and high levels of CRF specifically,” write study authors Marcel Ballin, PhD, et al. “Our findings add reassuring evidence on the safety and benefits of high adolescent CRF, which may alleviate concerns about potential long-term arrhythmic harm.”