Not that facts will get in the way of idiots, but I'll give it a try:
New large study from New England Journal of Medicine 10/18/2018 :
Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing
Design, Setting, and Participants This retrospective cohort study enrolled patients at a tertiary care academic medical center from January 1, 1991, to December 31, 2014.Consecutive adult patients referred for symptom-limited exercise treadmill testing were stratified by age- and sex-matched cardiorespiratory fitness into performance groups: low (under 25th percentile), below average (25th-49th percentile), above average (50th-74th percentile), high (75th-97.6th percentile), and elite (≥97.7th percentile).
Exposures Cardiorespiratory fitness, as quantified by peak estimated metabolic equivalents on treadmill testing.
Main Outcomes and Measures All-cause mortality.
Results The study population included 122 007 patients (mean [SD] age, 53.4 [12.6] years; 72 173 [59.2%] male). Death occurred in 13 637 patients during 1.1 million person-years of observation. ... Extreme cardiorespiratory fitness (≥2 SDs above the mean for age and sex) was associated with the lowest risk-adjusted all-cause mortality compared with all other performance groups.
Conclusions and Relevance Cardiorespiratory fitness is inversely associated with long-term mortality with no observed upper limit of benefit. Extremely high aerobic fitness was associated with the greatest survival and was associated with benefit in older patients and those with hypertension. Cardiorespiratory fitness is a modifiable indicator of long-term mortality, and health care professionals should encourage patients to achieve and maintain high levels of fitness.
TLDR: Keep running marathons, you'll live longer.