Youth fitness benefits outweigh arrhythmia risk

High adolescent fitness was linked to net long-term cardiovascular benefit.
*Nationwide cohort with sibling control; Level 2 (OCEBM).

Citation

Ballin M, Carlsson AC, Wändell P, et al. Circulation. 2026;154:7-15. doi:10.1161/CIRCULATIONAHA.125.078250

Background

High youth fitness is generally heart-protective, but prior studies suggested very fit young people may have more atrial fibrillation. This study tested whether that apparent risk persisted after comparing full siblings, which helps account for shared family factors.

Patients

1,124,049 Swedish men, mean age 18.3 years, undergoing mandatory military conscription from 1972 to 1995. Exclusions included missing fitness or covariate data, extreme fitness values, and extreme body mass index values; women were not included.

Intervention

Highest tenth of adolescent cardiorespiratory fitness measured by maximal bicycle testing.

Control

Lowest tenth of adolescent cardiorespiratory fitness.

Outcome

First atrial fibrillation diagnosis or death, and first non-atrial fibrillation cardiovascular disease diagnosis or death.

Follow-up Period

Until December 31, 2023; up to about 5 decades.

Results

Sibling-controlled comparisonAbsolute risk differencePractical meaning
Non-atrial fibrillation cardiovascular disease by age 35 (primary)0.11% lowerAbout 909 associated with one fewer event
Non-atrial fibrillation cardiovascular disease by age 65 (primary)3.91% lowerAbout 26 associated with one fewer event
Atrial fibrillation by age 65 (primary)2.30% higherAbout 44 associated with one extra event

In population-wide analysis, early atrial fibrillation risk briefly exceeded cardiovascular benefit. In sibling comparisons, that trade-off disappeared: no age window showed net cardiovascular disadvantage. Results were observational, not randomized.

Limitations

Only Swedish men were studied, limiting generalizability. Fitness was measured once in adolescence. Smoking, alcohol use, physical activity, and body composition were unavailable. Registry diagnoses may miss milder disease. Sibling analyses reduce but cannot eliminate confounding.

Funding

No funding; several authors reported industry honoraria/advisory roles.

Clinical Application

Encourage youth fitness; this study reassures that small atrial fibrillation excess is outweighed by broader cardiovascular benefit.