Adolescent Cardiorespiratory Fitness and the Trade-Off Between Atrial Fibrillation Risk and Cardiovascular Benefits: A Nationwide Sibling-Controlled Cohort Study
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 comparison | Absolute risk difference | Practical meaning |
|---|---|---|
| Non-atrial fibrillation cardiovascular disease by age 35 (primary) | 0.11% lower | About 909 associated with one fewer event |
| Non-atrial fibrillation cardiovascular disease by age 65 (primary) | 3.91% lower | About 26 associated with one fewer event |
| Atrial fibrillation by age 65 (primary) | 2.30% higher | About 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.
Discussion
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In this sibling-controlled cohort study, high adolescent cardiorespiratory fitness was associated by age 65 with RD +2.30% for atrial fibrillation and −3.91% for non-AF CVD versus the lowest fitness decile. Given the observational design cannot prove causality, how valid and applicable are these findings for counseling youth about high fitness? In this nationwide cohort study, why did comparing full siblings strengthen the authors’ assessment of the association between adolescent cardiorespiratory fitness and later atrial fibrillation/non-AF cardiovascular disease?