The well-held belief that physical fitness in youth directly causes a lowered risk of early death is being challenged by new research from Uppsala University, which suggests that the true relationship between fitness and mortality may be far more complex than previously thought. The findings, published in the European Journal of Preventive Cardiology, reveal that even random factors—such as accidents—show similar associations to fitness and premature death as diseases, raising questions about the validity of past conclusions on the protective effects of fitness alone.
Thai readers may be familiar with the advice that regular exercise and strong cardiorespiratory fitness will significantly lower risks of dying from diseases like heart disease or cancer. This message is echoed in countless public health campaigns and even reflected in Thailand’s own Ministry of Public Health guidelines. The new Swedish study, however, highlights how observational studies—on which these recommendations are often based—may overstate the effects of fitness due to unaccounted factors.
The researchers tracked over 1.1 million Swedish men, all conscripted for military service between 1972 and 1995 at approximately age 18. Participants were grouped according to their fitness level and followed up to their 60s using national health and mortality registries. Consistent with earlier studies, those with higher adolescent fitness showed lower risk: a 58% reduction in cardiovascular deaths, a 31% reduction in cancer deaths, and a 53% overall reduction in mortality compared to those with the lowest fitness.
Yet, when researchers used a technique known as negative control outcome analysis—looking at deaths from random accidents, such as car crashes, drownings, and homicides—they found almost identical reductions: a 53% lower risk among the fittest individuals. In theory, cardiorespiratory fitness in youth should not protect against random accidents, which are unrelated to disease and typically occur by chance.
Lead researcher, an associated epidemiologist, explained, “It surprised us that the association with accidental mortality reflected the other associations, even after we controlled for all the factors that siblings share. This underlines how strong the assumptions are that you make in observational studies, since it appears to be very difficult to create comparable groups. The consequences may be that you overestimate the magnitudes of the effects you find.”
To strengthen their findings, the team also used a sibling comparison design, examining brothers with different fitness levels. This controlled for shared family and environmental factors, offering a more rigorous test of the effect. Still, the association persisted, suggesting that something besides fitness itself—perhaps personality, social factors, or genes—was influencing the risk.
These results align with other international research, including twin studies and genetic studies that suggest some genes may jointly increase both enthusiasm for physical activity and lower disease risk. The idea that survivors in higher fitness groups might also possess other traits—like risk aversion, conscientiousness, or socioeconomic advantages—offers a plausible explanation. “That the effects of good cardiorespiratory fitness may be overstated might sound controversial to some, but the fact is that if you look at the results from studies others than traditional observational studies, a more nuanced picture does emerge,” the lead author said.
The findings carry important implications for public health in Thailand, where policies and health interventions often aim to increase population fitness in hopes of reducing chronic disease. While exercise has proven benefits—improving quality of life, mobility, and mental health—the precise magnitude of its effect on longevity may need to be re-evaluated, especially before investing in large-scale interventions. As the lead researcher noted, “Large-scale interventions or policy changes intended to apply to the entire population must be based on reliable estimates—otherwise there is a risk of expecting effects that have in fact been overestimated.”
Importantly, this research does not advise abandoning exercise; rather, it calls for greater methodological rigor, and the use of multiple research designs to truly understand the effect size of fitness on various health outcomes. “Our results should not be interpreted as if physical activity and exercise are ineffective or that you should not try to promote it. But to create a more nuanced understanding of how big the effects of fitness actually are on different outcomes, we need to use several different methods,” the lead author added.
For Thai society, the lessons are multifaceted. First, physical activity remains a central pillar of a healthy lifestyle, supporting physical and mental well-being amid urbanization, work stress, and aging demographics. However, policymakers and the public alike should recognize that health depends on a broader set of factors, including genetics, socioeconomic status, healthcare access, and even accident prevention.
Cultural context is key: Thais have long valued traditional activities such as walking, cycling, and communal exercises like aerobics in public parks—a familiar scene around Bangkok’s Lumpini Park in the evening. Yet, as the country continues to modernize and faces an increase in non-communicable diseases, nuance in public health messaging is essential to set realistic expectations.
Looking forward, researchers are encouraged to employ methodologies such as negative control outcome analysis and sibling-comparisons to minimize confounding and clarify causality. This could help shape more precise health recommendations and interventions in Thailand, taking into account local customs and the full complexity of what influences lifespan.
For now, Thai readers are advised to continue regular physical activity for its wide range of benefits, while understanding that avoiding premature death involves many factors—some well beyond our individual control. Policy makers should critically assess the evidence before designing sweeping fitness interventions, ensuring public resources are invested based on the most reliable and nuanced science.
For further reading, see the original study report at News-Medical.net and published findings in the European Journal of Preventive Cardiology, along with background on lifestyle and health trends in Thailand from the Ministry of Public Health.