Key result
High adolescent fitness linked to a ~4% reduction in non-AF CVD, outweighing excess AF risk.
Why the study?
Whether the higher risk of AF in young athletes and high-fitness adolescents reflects causal effects or shared familial factors remains uncertain.
Does high adolescent cardiorespiratory fitness increase the risk of atrial fibrillation compared to its cardiovascular benefits in young men?
Cohort (n=1,124,049)
Yes
Does high adolescent cardiorespiratory fitness increase the risk of atrial fibrillation compared to its cardiovascular benefits in young men?
Effect estimate: RD -3.91% (non-AF CVD) / RD 2.30% (AF) at age 65 (95% CI -5.40% to -2.42% (non-AF CVD) / 1.15% to 3.45% (AF))
High adolescent cardiorespiratory fitness is associated with a small excess risk of atrial fibrillation that is outweighed by larger reductions in non-AF cardiovascular disease later in life.
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Captured external expert commentary on this paper, strongest first. Original sources are linked where available.
“Our study shows that there are good reasons to nuance and tone down the message, which has been widespread at times, that high levels of fitness or participating in races would pose a big risk to a person's cardiovascular health. The risk of atrial fibrillation is certainly not zero, but that said, the benefits are significantly greater.”
“We were then able to see that the age-dependent effect disappeared. Instead, we saw that the net effect was positive from the start, and that the benefits were greater as age increased. From a lifelong perspective, the findings show that the benefits of high levels of fitness outweigh the risks.”
Net benefit of high adolescent fitness may outweigh AF risk; extends sibling-controlled observations but leaves causal effects open.
BACKGROUND: Young athletes and adolescents with high cardiorespiratory fitness appear to have a higher risk of atrial fibrillation (AF), but the extent to which this reflects causal effects or shared genetic, behavioral, and environmental factors remains uncertain. METHODS: This cohort study with sibling control analysis comprised Swedish men who participated in mandatory military conscription examinations from 1972 to 1995 and completed cardiorespiratory fitness testing. The outcomes were AF and non-AF cardiovascular disease (CVD; eg, stroke and ischemic heart disease), defined as a composite end point of diagnosis or death in the National Patient Register and the Cause of Death Register, until December 31, 2023. Flexible parametric regressions estimated standardized cumulative risk differences (RDs) by deciles of fitness. RESULTS: Among 1 124 049 men (mean age, 18.3 years), 45 179 (4.0%) experienced an AF event and 96 404 (8.6%) had a non-AF CVD event at a median age of 54.8 and 54.4 years. In population-wide analysis controlling for measured confounders, compared with the lowest decile of fitness, the highest decile had a small excess in AF that exceeded the reduction in non-AF CVD during early adulthood, whereas the reduction in non-AF CVD became larger from 45 years of age onwards. In full-sibling comparisons controlling for shared familial factors, the age-dependent trade-off disappeared entirely, leaving no age window with a net cardiovascular disadvantage. Already from 35 years of age, the reduction in non-AF CVD was larger (RD, -0.11% [95% CI, -0.21% to -0.01%]) than the excess in AF (RD, 0.06% [95% CI, -0.01% to 0.12%]). By 65 years of age, the gap further widened, with an even larger reduction in non-AF CVD (RD, -3.91% [95% CI, -5.40% to -2.42%]) compared with the excess in AF (RD, 2.30% [95% CI, 1.15%-3.45%]). CONCLUSIONS: High adolescent cardiorespiratory fitness is associated with a small excess in AF risk during early adulthood that is outweighed by larger reductions in non-AF CVD after controlling for familial confounders. These findings support population-level efforts to improve youth cardiorespiratory fitness and provide reassurance about the safety and benefits of high fitness levels.
Journal, society, and media accounts. Useful signal, not independent expert judgment.
Ballin et al. (2026) conducted a cohort in Atrial fibrillation and cardiovascular disease (n=1,124,049). High cardiorespiratory fitness (highest decile) vs. Lowest decile of fitness was evaluated on Atrial fibrillation (AF) and non-AF cardiovascular disease (CVD) (RD -3.91% (non-AF CVD) / RD 2.30% (AF) at age 65, 95% CI -5.40% to -2.42% (non-AF CVD) / 1.15% to 3.45% (AF)). High adolescent cardiorespiratory fitness is associated with a larger reduction in non-AF CVD (RD -3.91%) than the excess in AF risk (RD 2.30%) by age 65 after controlling for familial confounders.
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