We often hear of cases in the media describing the deaths of marathoners or other distance runners. Ryan Shay, Jim Fixx, and Pheidippides* are all high profile runners who tragically collapsed and died while running. However, let’s make one thing clear, running is good for you! Since the 1950s studies have confirmed that exercise improves cardiovascular health and decreases your susceptibility of dying during a given period (A.K.A. mortality). So, we know that running is healthy, but how much should we run and how intensely should we run for maximum health benefits? A study published in the Journal of the American College of Cardiology in February 2015 suggests that light and moderate jogging 2-3 times per week is most beneficial in terms of reducing overall mortality when compared to a sedentary lifestyle. Higher-intensity jogging did not show any reductions in mortality compared to sedentary folks.
In terms of aerobic exercise, current Center for Disease Control and Prevention (CDC) guidelines on exercise recommend, “2 hours and 30 minutes (150 minutes) of moderate-intensity aerobic activity (i.e., brisk walking) every week,” or, “1 hour and 15 minutes (75 minutes) of vigorous-intensity aerobic activity (i.e., jogging or running) every week.” Most studies have found that regular exercise reduces mortality compared to sitting on your butt all the time. Some studies have tracked exercisers and non-exercisers over decades and found that physically active people have about a 30% reduction in risk of death during the study period.
The 2015 study by researchers involved with the Copenhagen City Heart Study focused on studying the relationship between the pace, amount, and frequency of jogging and overall mortality. They studied a randomly selected group of healthy joggers (1,098 men and women) and non-joggers (3,950 men and women), all individuals were white in this study group. Anybody in this group with a history of coronary stroke, heart disease, or cancer was excluded from the study. Patients were followed-up from 2001-2013 or until their death, so the period of time studied was about 12 years. Using a survey the researchers assessed the quantity of jogging, frequency of jogging, and a relative perception of running intensity. To assess the influence of running on mortality joggers were split into 3 groups, light joggers, moderate joggers, and strenuous joggers** based on their amount and intensity of jogging or “dose”. The study analyzed the relationship between quantity of jogging, frequency of jogging, and a relative perception of running intensity and overall mortality using a statistical technique called the Cox proportional hazards regression analysis. Basically, this analysis method examines the treatment effect (quantity, frequency, and intensity of joggin) on survival after adjusting for other potential explanatory values (age, sex, smoking, alcohol consumption, education, and diabetes).
Overall, joggers had fewer deaths (28) than sedentary non-joggers (128). The optimal jogging “dose” for reduced mortality was jogging at a slower or moderate pace for 1 to 2.4 hours per week at a frequency of 2-3 times per week. Out of the light, moderate, and strenuous jogger groups the hazard ratio (mortality risk) was significantly (see central illustration from the paper below) lower than the moderate and strenuous joggers. Strenuous joggers did not have a mortality risk that was any different (statistically speaking) than sedentary individuals. Looking at the figure below, the authors point out that the dose-response curve or running “dose” versus hazard ratio is U-shaped or J-shaped.
There are a few drawbacks to this study and it doesn’t quite prove that strenuous exercise actually has an equal mortality rate with a sedentary lifestyle. One caveat is that all levels of activity were self-reported and one individual’s perception of strenuous versus non-strenuous exercise is very subjective. Also, the low, moderate, and strenuous jogger groups seem somewhat arbitrarily define. Another point is that compared to other treatment groups the strenuous jogger group confidence intervals are quite large and overlap with some of the other treatments, this could be due to a small sample size. However, the study authors state that the strenuous jogging group mortality risk is significantly higher than the light jogger group. This is also a correlative study and can only show associations between running and mortality and cannot prove any causal relationships. So, while the findings of this study are interesting and definitely continue to show that light and moderate exercise is associated with lower mortality rates, it hints at but doesn’t really prove that running at higher paces, mileages, and number of runs per week is dangerous.
*some historians do not believe that Pheidippides, a professional running courier, died after running a marathon to Athens to proclaim a Greek victory over the Persians in the Battle of Marathon. Some believe that the story is a romantic invention, others believe that after reaching Athens he continued on running to Sparta (another 137 miles).
**Light joggers ran 3 times or less each week, for less than 2.5 hours of running each week, and at a slow or average pace of ~5 miles per hour (12 minute mile). Moderate joggers fit several conditions. They ran at slow or average pace (5-7 miles per hour, or between a 12-8:34 minute mile), with 2.5 or more hours of running per week less, and went on 3 or fewer runs per week. Moderate runners were also considered those runners who ran at a fast pace of more than 7 miles per hour (less than an 8:34 mile) for 4 hours or less per week at a frequency of 3 or fewer jogs per week. Additionally, moderate runners were those with a slow or average pace running more than 3 time per week or a fast pace running less than 2.5 hours per week for more than 3 runs per week. Joggers in the strenuous category had a pace of more than 7 miles per hour (less than an 8:34 mile) and greater than 4 hours of jogging per week or alternatively 2.5 hours or more of jogging time more than 3 times per week.