Running for Your Life? Not So Much
The New York Times, Runner’s World, and a host of other media outlets recently hyped a new study published in Progress in Cardiovascular Diseases on the benefits of running. The study asserts that running, if performed regularly, leads to 3.2 additional years of life. From the authors:
Running still provides 2.8 years of additional life even after subtracting the total running time of 0.43 years from the 3.2 years of extended life. . . . Therefore, a net “running” to “longevity benefit” ratio is roughly 1:7 (0.43:2.8), suggesting 1 hour of running provides an additional 7 hours of extended life.
Sounds great? Look more closely. Imagine if you invested $1 today and were guaranteed $7 in return. You can’t judge if that is a good return on investment because there is a critical piece of information missing: time. For example, $1 invested in the S&P 500 in 1981 would be worth about $50 today. The same logic can be used to analyze the results of the new running study.
The study compares the “investment” of running an average of two hours a week for 36 years (3,744 hours) with the “return” of 2.8 additional years (24,500 hours) tacked on to the end of your life. Think of this like contributing $2/week from the age of 44 to 80 to your 401k and eventually accumulating $24,500 in retirement savings. Is this a good investment? The study, along with the media reporting on it, certainly suggests that it is.
To answer this question ourselves, we can turn to a simple mathematical tool: cost-benefit analysis. Simply replace hours with dollars, and compare the discounted net present value (NPV) of running (the cost) with the NPV of the additional longevity (the benefit).
Using a 10 percent discount rate, the present value cost of running two hours a week for 36 years is 1,006 hours, while the discounted present value benefit of 3.2 years is just 824 hours. Put differently, if you discount the value of your future time similar to the average returns earned in a diversified stock portfolio, running for longevity yields a below average return, not the phenomenal return the media implies.
There is, however, an additional factor to consider: roughly one-third of the additional hours of longevity will be spent sleeping. Much like a capital gains tax on investment, sleep will reduce the return. The seven additional hours would really be about five waking hours. Accounting for time spent sleeping reduces the NPV of longevity from 824 hours to 577 hours – 42 percent less than the calculated cost.
Of course, a weakness of long-duration cost-benefit analysis is that the results are dependent on the assumed discount rate. While an assumed 10 percent discount rate implies running to be an irrational strategy for achieving longevity, a 7.7 percent discount rate yields a “break-even” cost-benefit result. However, the economic literature indicates that many consumers’ implied discount rates are much higher, often higher than 20 percent. This result may be due, in part, to “hyperbolic discounting” – that is, consumers discounting events far into the future at annual rates much higher than shorter-term tradeoffs. This may explain why 80 percent of U.S. adults don’t exercise as much as is recommended.
In the end, running may be a worthwhile endeavor, but for reasons more obvious and tangible than the alleged “promise” of additional years later in life (years potentially marred by sickness or immobility). Running can make you feel and look good, and it can be enjoyable. However, time is valuable so don’t run for your life if it means not spending time living your life.
The media coverage of the study and “click bait” embedded in the study itself would lead us to believe that only a fool wouldn’t lace up their sneakers to take advantage of such a simple way to extend their life. But as with many things that blow up our social media feeds, there’s more to it than meets the eye.
Alex Brill is a research fellow at the American Enterprise Institute. In his free time, he enjoys running an occasional leisurely 30-minute 5k.