Some recent headlines have some reconsidering going for their next jog!
Could this be true? The media would never sensationalize such a topic, right? Let's clarify.
These articles were based on a recent research study titled, "Dose of Jogging and Long-Term Mortality: The Copenhagen City Heart Study", published in the Journal of the American College of Cardiology.6
The study followed a group of 1,098 joggers and 413 inactive, nonjoggers (aged 20 to 92 years of age) from 2001 to 2013. In 2001 to 2003 participants were asked about their jogging habits, and were followed until 2013 to determine who had died (i.e. mortality).
Overall, they support the importance of physical activity – finding that 2.6% of the joggers had died by 2013, while 31% of the inactive, nonjoggers died.
However, when all 4 groups of joggers were looked at, the 'strenuous jogger' and 'moderate jogger' did not differ in a 'hazard ratio' (explained below) for all-cause mortality (dying from anything) than the sedentary nonjoggers.
And it was these results that the media took off with.
Some Key Points of Caution
Despite being a very interesting and intriguing study, there are some key points that help us interpret these results with caution.
- There were only 36 'strenuous joggers' in the study's final analysis, compared to 394 sedentary non-joggers. These limited participants caution generalizing results, especially when dealing with probabilities of dying in the future.
- As shown in the following figure, only 5.5% strenuous joggers died over the 10 years (2 of the 36 people), while 30% of the sedentary non-joggers died (120 of the 394). In addition, only 1.2% and 3.1% died in the light and moderate jogging groups, respectively – again, compared to 30% in the sedentary nonjogger group!
Why didn't the media focus on these results!? The headline...
"New study confirms, physical activity is still awesome: To be added to lyrics of popular Lego® Movie song."
- The jogging amounts were measured in 2001-2003, at one time point. We have no idea of knowing whether or not their physical activity changed (for better or worse) until 2013. Can we really say that their self-reported jogging at one time point (in 2001) is the reason they died in 2013?
- The sedentary nonjoggers were more obese, nearly 20 years older, and had 5-6 times higher prevalence of hypertension and diabetes, compared to the joggers in the study.
- Other important behaviors, such as dietary behavior, were not taken into account.
So, what is the big deal with these hazard ratios? Well, See the figure below from the actual study.
The red dots represent the 'hazard ratio' of that particular jogging group – which is the probablility that someone in that group, who has not died by 2013, will die by the next measured time point.
However, if the horizontal line on either side of the red dot (the confidence interval) crosses the vertical dotted line (hazard ratio = 1.0), then those results are considered to be at no higher or lower risk than the reference group of sedentary nonjoggers.
Because the 'strenuous jogger' and 'moderate jogger' lines cross the vertical dotted line, they are not statistically significantly different than the sedentary nonjogger group. The authors conclude,
"Light and moderate joggers have lower mortality than sedentary nonjoggers, whereas strenuous joggers have a mortality rate not statistically different from that of the sedentary group."
Actually, it was only the light joggers (in bottom part of figure) who were found to be at lower risk than the sedentary nonjogger – once some other variables were accounted for (age, sex, smoking, smoking, alcohol use, education level, and who had diabetes).
NOTE: Since hazard ratio results can only be applied within the time frame of the study, and the outcomes should not be broadly inferred – as the popular media is trying to do.
A New Topic?
Despite the recent attention, this not a new topic. Overtraining has long been an area of concern for athletes, including the physiological and psychological consequences. The more recent transition has come in regards to the concern that excessive aerobic exercise can cause overuse damage to the heart and cardiovascular system – which I believe is a legitimate concern, and needed area of research.
- In 2012, a study presented as an abstract at a conference, found that those running ≥ 20 miles per week did not have a lower hazard ratio of dying from all-causes of death than those running 0 miles per week.1
- Also in 2012, a previous study from the Copenhagen City Heart Study followed 20,000 Danes since 1976, and found that joggers lived 6 years longer than non-runners, while also having a 44% lower risk of death during the study.4
A Controversial Topic?
Can we now add exercise to the list of 'too much of a good thing'? The jury is still out, as such findings are seemingly in contrast to years of research that has found a dose-response relationship with mortality and exercise amounts or fitness levels – 'the more the merrier.'
- For example, previous research has found that high levels of fitness are still at much less risk of mortality than sedentary, non-active individuals.2
- Another popular study found that 45 minutes/day of vigorous physical activity has more than twice the survivial benefit than 45 minutes/day of light to moderate exercise.7
- Perhaps more interesting, another study from the same Copenhagen City Heart Study following 19,329 men and women (aged 20-93) concluded that, "Long-term moderate or high physical activity was in both sexes associated with significantly lower mortality from coronary heart disease, cancer and all-causes."5
Despite what the media would have us think about this research, we must not lose sight of:
- Keep jogging! The study's results do not conflict with current physical activity guidelines, rather re-emphasize the importance of physical activity.
** The authors found that even < 1 hour of jogging per week or one time per week was associated with significantly lower risk than not being active at all.
- The study of interest, although intriguing, has too many limitations to draw any major conclusions. Way more research is needed to conclude that too much exercise is as bad as being a couch potato – especially in light of the research showing the benefits of higher amounts of exercise in reducing risk of death.
- The concern here, if there is one, is for those who exercise to extreme amounts. These results do not even concern most people – who are not training for multiple marathons and beyond.
** For most of us, we are active within the normally prescribed range – 150 minutes per week of moderate intensity aerobic activity – and we are enjoying the many wonderful benefits.
- Lee, D. C., Pate, R. R., Lavie, C. J., & Blair, S. N. (2012). Running and all-cause mortality risk - Is more better? Medicine and Science in Sports and Exercise, 44, 924-924. Annual Conference, San Francisco, CA: S699.
- Lee, D. C., Sui, X., Ortega, F. B., Kim, Y. S., Church, T. S., Winett, R. A., ... & Blair, S. N. (2010). Comparisons of leisure-time physical activity and cardiorespiratory fitness as predictors of all-cause mortality in men and women.British Journal of Sports Medicine, bjsports66209.
- O'Keefe, J. H., & Lavie, C. J. (2013). Run for your life… at a comfortable speed and not too far. Heart, 99(8), 516-519.
- Schnohr, P. (2012). Assessing prognosis: A glimpse of the future. Jogging healthy or hazard. EuroPRevent. In: Cardiology ESo, Ed. EuroPRevent 2012. Dublin, Ireland: European Heart Journal.
- Schnohr, P., Lange, P., Scharling, H., & Jensen, J. S. (2006). Long-term physical activity in leisure time and mortality from coronary heart disease, stroke, respiratory diseases, and cancer. The Copenhagen City Heart Study. European Journal of Cardiovascular Prevention and Rehabilitation, 13(2), 173-179.
- Schnohr, P., O’Keefe, J. H., Marott, J. L., Lange, P., & Jensen, G. B. (2015). Dose of jogging and long-term mortality: the Copenhagen City Heart Study. Journal of the American College of Cardiology, 65(5), 411-419.
- Wen, C. P., Wai, J. P. M., Tsai, M. K., Yang, Y. C., Cheng, T. Y. D., Lee, M. C., ... & Wu, X. (2011). Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study. The Lancet, 378(9798), 1244-1253.