Is Fitness Overrated? Study Questions the True Impact of Fitness on Early Death

The study analysed data from over 1.1 million Swedish men conscripted for military service between 1972 and 1995, with an average age of 18 at the time. These men were grouped by fitness levels and followed until their 60s or death, with researchers accessing cause-of-death data through the National Cause of Death Register. The initial analysis confirmed previous findings: the most physically fit had a 58% lower risk of dying from cardiovascular disease, 31% lower risk from cancer, and 53% lower risk of all-cause mortality compared to the least fit group.

However, when the researchers turned their attention to deaths from random accidents, such as car crashes, drownings, and homicides, they found a 53% lower risk among the fittest men as well. Given that physical fitness should not significantly impact the likelihood of dying in random accidents, this result suggests the presence of confounding factors. This method, known as negative control outcome analysis, casts doubt on the assumption that the observed associations are purely due to fitness.

"Our results should not be interpreted as if physical activity and exercise are ineffective or that you should not try to promote them. But to create a more nuanced understanding of how big the effects of fitness are on different outcomes, we need to use several different methods. If we just ask the question in the same way, we will always get the same answer. It's only when we get the same answer to a question that we have asked in slightly different ways that we can be sure that the findings are accurate," says Marcel Ballin, associated researcher in epidemiology and lead author of the study.

Reference: https://www.uu.se/en/news/2025/2025-05-15-the-effect-of-physical-fitness-on-mortality-is-overestimated