Too Much of a Good Thing May Kill You!
We are constantly told that exercise is good for us, and there is overwhelming scientific evidence that this is true. Regular physical activity reduces the risk of heart disease, diabetes, obesity and premature death. But does it follow that the more exercise we undertake, the healthier we become? Not necessarily. Research suggests that there may be limits beyond which additional exercise provides little benefit and, in some circumstances, could actually become harmful.
A study published in the Mayo Clinic Proceedings in 2014 examined 2,377 people who had previously suffered heart attacks. Researchers followed them for an average of approximately ten years, comparing their exercise habits with their subsequent risk of death from cardiovascular disease. The results were striking. Moderate exercise substantially reduced cardiovascular mortality, with the most active groups below a certain threshold experiencing reductions of up to 63 per cent compared with those exercising very little. However, among participants undertaking the greatest amounts of exercise, much of this apparent protection disappeared.
The researchers found that cardiovascular mortality initially declined as exercise increased, but the benefits appeared to reverse at very high exercise levels. Those running the equivalent of more than approximately 50 kilometres per week appeared to lose much of the protection enjoyed by somewhat less active participants. This did not mean that the heaviest exercisers were demonstrably worse off than people who barely exercised. Rather, the study suggested that excessive exercise might cancel some of the benefits obtained from more moderate activity.
There are important qualifications. The study concerned people who had already suffered heart attacks, not healthy individuals. Relatively few participants undertook the highest levels of exercise, and the findings were observational rather than proof that excessive exercise caused additional deaths. Nevertheless, the results raise an interesting question: can the human body suffer from too much of something that is ordinarily beneficial?
Other research has raised similar concerns about extreme endurance exercise. Some studies have found that lifelong endurance athletes have higher rates of certain heart rhythm disturbances, particularly atrial fibrillation. Researchers have also investigated whether repeated extreme physical exertion might contribute to changes in heart tissue or increased coronary artery calcification. However, these findings do not establish that ordinary vigorous exercise damages the heart. Indeed, large studies generally show that physically active people live longer than inactive people, even when their exercise levels are relatively high.
The broader lesson is that the human body does not necessarily operate according to the principle that more is always better. Consider vitamins. They are essential for health, but excessive doses of certain vitamins can be toxic. Sunlight helps the body produce vitamin D, but excessive exposure increases the risk of skin cancer. Water is indispensable for life, yet drinking extraordinary quantities can produce dangerous disturbances in blood sodium levels. Even healthy activities have limits.
The ancient Greeks understood this principle through the idea of the golden mean. Aristotle argued that virtue generally involved avoiding the extremes of excess and deficiency. Although this philosophical principle cannot determine the ideal amount of exercise, it provides a useful reminder that moderation often makes more sense than pursuing extremes.
There is also a psychological dimension. Modern fitness culture sometimes encourages people to believe that greater effort, longer training sessions and ever-increasing physical challenges must produce better health. Yet the objective of exercise should be improved health and physical functioning, not simply the accumulation of kilometres or hours of exertion. Recovery, adequate nutrition and sensible training are important parts of maintaining fitness.
None of this provides an excuse for inactivity. The overwhelming problem in modern societies is insufficient exercise, not excessive exercise. Regular walking, swimming, cycling, resistance training and other forms of physical activity provide substantial benefits. Most people would improve their health by becoming more active rather than less active.
The lesson from the heart-attack survivor research is therefore not that exercise is dangerous, but that its benefits may have limits, particularly for people with existing cardiovascular disease. What is beneficial in moderate quantities does not necessarily become more beneficial when taken to extremes.
The sensible objective is to exercise regularly, maintain strength and cardiovascular fitness, and allow adequate recovery. Those with established heart disease should seek medical guidance before undertaking unusually demanding training programmes. For the rest of us, the evidence strongly supports remaining physically active without assuming that ever-greater exercise volumes must produce ever-greater benefits.
The central lesson is simple: exercise is essential for good health, but more is not necessarily better. Sometimes enough really is enough.
https://www.mayoclinicproceedings.org/article/S0025-6196(14)00437-6/abstract
