Analysis of a large epidemiological database here shows that sufficient exercise correlates with a halving of the risk of mortality due to influenza. Like many other studies, it also shows that too much exercise may be harmful, actually increasing the risk of mortality. While correlation does not imply causation, there is plenty of evidence for physical fitness and physical activity to reduce impacts of aging related to immune function. Alternative explanations revolve around the tendency of more robust individuals to conduct more exercise, while also tending to be more resilient independently of the effects of exercise.
A nationally representative sample of US adults (aged ≥18 years) who participated in the National Health Interview Survey from 1998 to 2018 were followed for mortality through 2019. Participants were classified as meeting both physical activity guidelines if they reported ≥150 minutes/week of moderate-intensity equivalent aerobic physical activity and ≥2 episodes/week of muscle-strengthening activity. Participants were also classified into five volume-based categories of self-reported aerobic and muscle-strengthening activity.
Among 577,909 participants followed for a median of 9.23 years, 1,516 influenza and pneumonia deaths were recorded. Compared with participants meeting neither guideline, those meeting both guidelines had 48% lower adjusted risk of influenza and pneumonia mortality. Relative to no aerobic activity, 10-149, 150-300, 301-600 and greater than 600 minutes/week were associated with lower risk (by 21%, 41%, 50% and 41%). Relative to fewer than 2 episodes/week of muscle-strengthening activity, 2 episodes/week was associated with 47% lower risk.
At the opposite end, we found that ≥7 muscle-strengthening activity episodes/week was associated with an increased risk. A J-shaped dose-response between muscle-strengthening activity and all-cause mortality has been observed elsewhere. While beyond the scope of this study, plausible explanations range from inaccurate responses (such as reporting occupational physical activity, which may not confer the same protective effect as leisure-time physical activity) to haemodynamic ramifications of frequent, high-intensity activity.