Longevity Briefs: The Not-So-Simple Link Between Exercise And Longevity

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

We all know exercise is good for us. But how good? And how much physical exercise is necessary? While many observational studies link physical activity to lower mortality risk, the evidence is often based on single time-point assessments. That is to say, participants that were exercising at the time of the study live longer, but there’s a lack of data on whether these people maintained consistent exercise throughout life. Observational studies also struggle to disentangle correlation from causation, and results can be further confounded by the complex interplay between genes and exercise. Here, a study aimed to address these gaps with a large, longitudinal twin study. Comparing twin pairs reduced the possible influence of genetic differences (or in the case of identical twins, rules them out entirely), while studies that follow participants over a long period of time provide a more complete picture of the benefits of long-term vs short-term exercise.

The discovery:

Researchers looked at data from the older Finnish Twin Cohort (FTC), a dataset following same-sex twins born before 1958. The study included 22,750 twins whose physical activity levels were measured using questionnaires in 1975, 1981, and 1990. Based on the responses, participants were categorized into four long-term physical exercise patterns: sedentary, moderately active, active, and highly active. Mortality data was then tracked until 2020.

After controlling for confounding factors, researchers found that the greatest reduction in mortality was in the moderately active group compared to the sedentary group, which represented a 7% reduction in mortality long-term. This increased to 16% when comparing only identical twins. Doing more exercise than this did not lead to a further statistically significant mortality reduction. However, when the researchers looked at this relationship in the shorter term, by looking at deaths only going up to 2011, they found that further increases in activity were associated with mortality reduction. This could be because people who were undertaking above-moderate levels of activity did not continue to exercise heavily into old age, and so did not maintain the benefits.

The researchers also looked at the relationship between exercise and biological ageing using epigenetic clocks. Epigenetic clocks are algorithms that look at molecular tags that are added to the DNA molecule throughout life in order to estimate how rapidly someone is ageing. They found that the relationship was ‘U-shaped’ – ageing was accelerated in those who exercised the least, but also in those who exercised the most.

The implications:

This study aligns with previous research suggesting that increasing levels of exercise yield diminishing returns when it comes to longevity long-term, possibly even becoming harmful at the highest levels. However, the level of benefit estimated here is a lot lower than suggested by most previous studies, including much larger studies. Many of those studies only take a ‘snap shot’ of physical activity, whereas the present study assessed activity at multiple moments in time over a 15 year period. The authors also note than when they relaxed their stringent compensation for confounding factors, they obtained figures closer to those of previous studies. This could imply that many studies do not sufficiently control for environmental and genetic confounding factors, leading them to overestimate the long-term benefits of exercise. The authors give smoking as an example: many studies control only for whether participants smoke or not, yet smokers who exercise generally smoke less than those who are sedentary.

This study is by no means challenging the notion that exercise is beneficial. It does suggest that the long-term benefits might have been overestimated, and also suggests that some benefits from higher levels of activity in earlier life might not persist into old age unless activity levels are maintained. However, even if exercise didn’t improve lifespan at all, it would still be highly valuable for the improvement in health and quality of life that results from being physically fit, not to mention the well established short-term mental health benefits.