Many More Reasons to Stay Fit: Aerobic Fitness Protects Against Chronic Disease

Every year, nearly three out of four deaths worldwide are caused by non-communicable diseases, primarily heart disease, cancer, diabetes, and lung diseases. Around 17 million people globally die from these conditions before reaching the age of 70. Aerobic fitness, which can be improved through physical activity, is considered one of the strongest factors in reducing the risk of dying from these diseases, alongside other risk factors such as age, sex, smoking, and genetic predisposition.

While the link between aerobic fitness and mortality from heart disease, vascular disease, and cancer has been well-established in many studies, other non-communicable diseases have been far less studied in this context. A new study now aims to bridge this knowledge gap by examining the connection between aerobic fitness and mortality from these other diseases.

A 30-Year Study on Fitness and Health

The study was based on data collected from 36,645 men residing in Dallas, USA, in their fourth and fifth decades of life, who participated in an ongoing study on chronic disease prevention between 1971 and 2003. For inclusion in the study, lifestyle habits such as diet, smoking, and physical activity were examined, and participants were asked to undergo a stress ECG test, which assesses physical fitness and heart function. Additionally, participants who were underweight, had abnormal ECG findings, or had a history of stroke, heart attack, or cancer were excluded from the study. This produced a sample that allowed researchers to examine the effect of fitness alone on otherwise healthy men.

Over 17 years of follow-up, 2,317 participants died, just over a quarter of them (694) from causes unrelated to heart disease or cancer. The risk of death increased with age and decreased as the participants’ fitness level improved. Even when adjusted for other risk factors—such as age, obesity, smoking, diabetes, hypertension, and high cholesterol—aerobic fitness remained an independent protective factor against death from diseases unrelated to heart disease and cancer. Compared to participants with low physical fitness, mortality from these other diseases was 43% lower in those with moderate aerobic fitness and 57% lower in those with high aerobic fitness.

When examining specific diseases, the protective contribution of physical fitness was evident.  High aerobic fitness was associated with up to an 83% reduction in mortality from diabetes or kidney disease, up to a 91% reduction from lung diseases, and a 66% reduction in mortality from acute infections. There was also a 28% reduction in mortality from injuries. The relationship between higher physical fitness and lower mortality was observed across all ages, body weights, and activity levels, strengthening the likelihood that aerobic fitness itself is a key protective factor, regardless of other health metrics.

Despite these positive findings, the study has several important limitations. First, aerobic fitness was measured only at baseline, making it unclear how it changed over time; consequently, the relationship between changes in fitness and mortality cannot be determined. Second, the measurement of fitness was not ideal: although it involved a demanding treadmill stress test, participants were required to reach at least 85% of their age-predicted maximum heart rate, based on a formula that may not be accurate for everyone. Moreover, although participants were categorized into three fitness levels using a recognized, standardized medical measure, the study’s conclusions may not apply to individuals with genuinely low fitness levels. In other words, a participant classified as “high fitness” relative to others in the study may not have met the medical definition of high fitness—making it difficult to generalize the findings to the broader population. Finally, it is possible that men with particularly high fitness levels were already in excellent health at the outset, and that their good health was simply reflected in their fitness.

The findings reinforce the understanding that aerobic fitness not only reflects overall health but also independently protects against a range of chronic diseases beyond heart disease and cancer. In a world where most deaths result from chronic illness, it is essential to measure physical fitness directly, rather than merely tracking physical activity, and to recognize fitness as a central objective in both disease prevention and treatment.

Future studies will need to track participants’ fitness levels over time rather than only at baseline, using standardized and comparable measures. They should also investigate the physiological mechanisms that connect physical fitness to mortality from each of the diseases examined. Equally important, future research must include women, broader age ranges, and populations from diverse countries and cultures.