Overview

• A study of over 1.1 million Swedish men found that higher fitness levels in late adolescence were linked to a 53% lower risk of all-cause mortality but also to a similar reduction in accidental deaths.
• The findings suggest that unobserved confounding factors, such as socioeconomic background and genetics, may explain the observed associations rather than fitness itself.
• Negative control outcomes, like accidental deaths, and sibling comparisons revealed that the fitness-mortality link is likely overstated due to bias in observational studies.
• Researchers recommend using advanced methods, including twin studies, Mendelian randomization, and cross-country analyses, to better understand fitness's true impact on longevity.
• Despite uncertainties about long-term mortality effects, physical activity during adolescence remains beneficial for mood, sleep, and overall mental health.