Does playing tennis make you live 9.7 years longer?

Episode Summary

Executive Summary: The episode examines a viral claim that tennis adds 9.7 years of life, tracing it to a Mayo Clinic study and evaluating whether the association is real or confounded by wealth, education, and general fitness. Expert Adam Jacobs says the study is decent but too small and observational to prove causation, though the adjusted result remains similar to the unadjusted one. The likely takeaway: tennis correlates with longer life, but we cannot say it causes it.

Main Topics: Viral claim about tennis and longevity (Priority: 5/5): The episode opens by addressing a social-media claim that tennis can extend life by 9.7 years and notes that the figure comes from a peer-reviewed study. Study design and strengths (Priority: 5/5): Adam Jacobs explains that the underlying study is unusually strong for this topic because it had over 8,000 participants, 25 years of follow-up, and a clear all-cause mortality outcome. Confounding by socioeconomic status (Priority: 5/5): The discussion tests whether tennis appears beneficial simply because players are wealthier, better educated, and generally healthier than non-players. Statistical adjustment and its limits (Priority: 4/5): The episode explains Cox proportional hazards regression and how adjusting for education, income, and other variables reduced the estimate only slightly, from 10.4 to 9.7 years, while still leaving measurement limitations. Small tennis-player sample size (Priority: 5/5): Despite a large overall cohort, only a small number played tennis, and only 16 deaths occurred in the adjusted tennis group, making the estimate vulnerable to random variation. Possibility that tennis is part of a broader active lifestyle (Priority: 4/5): The episode suggests the benefit may reflect playing multiple sports or being generally more active, especially since many tennis players also cycled in Denmark.

Key Arguments: The tennis longevity figure is based on a peer-reviewed observational study, so it is not invented, but it does not prove that tennis causes longer life. The study is relatively good for an observational analysis because it included more than 8,000 participants and followed them for 25 years. Socioeconomic confounding is a real concern because wealthier and more educated people tend to live longer, but adjustment only reduced the estimate from 10.4 to 9.7 years. The remaining association could still be biased because education and income were measured in broad categories and are hard to adjust for precisely. The tennis sample was small, especially after adjustment, so random chance may have produced an unusually large estimate. Tennis participants also played other sports frequently, so the observed effect may reflect an overall active, varied exercise pattern rather than tennis alone.

Data Points: Total participants: Over 8,000 - Size of the Danish cohort in the Mayo Clinic study Follow-up period: 25 years - Length of time participants were tracked for mortality outcomes Sports analyzed: 8 - The study compared longevity across eight sports Life expectancy gain from tennis: 9.7 years - Adjusted estimate reported for tennis players Life expectancy gain from tennis, unadjusted: 10.4 years - Estimate before adjusting for education, income, and other factors Life expectancy gain from badminton: 6.2 years - Reported estimate for badminton Life expectancy gain from soccer: 4.7 years - Reported estimate for soccer Life expectancy gain from cycling: 3.7 years - Reported estimate for cycling Life expectancy gain from swimming: 3.4 years - Reported estimate for swimming Life expectancy gain from jogging: 3.2 years - Reported estimate for jogging Life expectancy gain from calisthenics: 3.1 years - Reported estimate for calisthenics Life expectancy gain from health club activities: 1.5 years - Lowest reported gain among listed sports Tennis players in original group: 167 - Number of participants classified as tennis players before adjustment Tennis players in adjusted analysis: 111 - Number of tennis players remaining after adjustment Deaths among adjusted tennis group: 16 - All-cause mortality events in the adjusted tennis subgroup Cycling among tennis players: About 80% - Approximate share of tennis players who also cycled in Denmark

Pivotal Quotes: "Can we say that playing tennis makes you live 9.7 years longer? No, we cannot say that." — Adam Jacobs: Core conclusion on causation versus correlation "It may just be that they were lucky." — Adam Jacobs: Explanation for why the small tennis subgroup may have produced an inflated estimate "That tells me maybe it's not a massively strong confounding here, which surprised me." — Adam Jacobs: Assessment of how much socioeconomic confounding changed the result

Implications: Listeners should treat tennis-longevity claims as correlational, not causal. The episode reinforces why small subgroups, observational data, and incomplete confounder adjustment can mislead, even when a study sounds impressive.