The study authors, however, suggest that their findings should be treated with caution for a number of reasons. First, they note that only the healthiest and fittest individuals are able to compete in the tour, making it difficult to fairly compare them with the broader French community in which there are many men with prevalent chronic disease and illness. Second, participation in the Tour de France represents only a small time period in a cyclists' lifespan, limiting the ability to conclusively link participation in the tour with decreased mortality. Finally, the study authors were not able to directly estimate any effects of doping on cyclists.
"Due to a multitude of confounding factors, it is difficult to draw concrete and meaningful conclusions regarding the effects of endurance exercise itself on mortality from the data presented," said Abbas Zaidi, MD, and Sanjay Sharma, Department of Cardiovascular Sciences, St. George's University of London, UK, in a related commentary. Although providing food for thought, the study … ultimately leaves key questions on the optimal exercise dose and risk-benefit ratio of endurance sport unanswered."