Potential, but Unobserved, Adverse Cardiovascular Effects From Endurance Exercise

To the Editor:

The review by O'Keefe et al¹ in the June 2012 issue of Mayo Clinic Proceedings discusses the hypothesis that excessive strenuous exercise may result in adverse cardiovascular effects. Data from Wen et al² are cited as supportive evidence that the mortality benefits of exercise “peak at 50 to 60 minutes of vigorous exercise per day.” The reproduced figure, however, does not show a peak; rather, it possibly shows a plateau in the benefit of exercise at the highest level observed, and even the case for a plateau is unconvincing. Turning to the primary data, O'Keefe et al wrote a letter to the journal of publication³ and received a response that proved their interpretation to be incorrect. Wen et al⁴ responded to their letter with a description of data that show not only the absence of peak but also no evidence of a plateau, with a continuing trend to improved all-cause mortality and even better hazard ratios for cardiovascular disease at the highest level of exercise. Wen et al wrote, “We were not able to identify an upper limit of physical activity, either moderate or vigorous, above which more harm than good will occur… .” The interpretation of the data provided in the review by O'Keefe et al is misleading, particularly given the response of the authors of the original data.