I received this today, from Gabe Mirkin, MD's weekly newsletter:
Dr. Gabe Mirkin's Fitness and Health e-Zine
February 8, 2015
Slow Runners Don't Come Out Ahead
A new Danish study agrees with most previous studies that regular joggers as a group live longer than sedentary non-joggers (Journal of the American College of Cardiology, February 2, 2015). However, most of the news media reported that this study showed that slow, low-intensity joggers are less likely to die than intense exercisers ("Slow Runners Come Out Ahead," proclaimed the New York Times headline). The joggers who ran faster than 7 mph for more than four hours a week had the same death rate as the non-joggers. Joggers who moved at the very slow pace of 5 mph (12-minute miles) had a 49 percent lower risk of dying, while the faster joggers (7 mph pace) had a six percent lower risk of dying. A 7 mph pace (8 minutes, 36 seconds per mile) is fast for older people but slow for young ones. As a person ages, he loses strength and has to work much harder to run fast, so what is slow for a 20-year old can be fast for a 70-year old.
This study does not show that intense running is harmful. It implies that long, intense running does not prolong life compared to those who do not exercise, but there are no studies comparing the death rate in top marathon runners who run faster than 12 miles per hour (sub-5 mph pace) to those who jog slow and short. News reporters should have been suspicious of this study when it also reported that the optimal frequency of jogging was no more than three times a week. The majority of studies show that three times week is far less effective in promoting health and longevity than daily exercise.
Flaws in the Copenhagen Heart Study
The study followed 1,098 healthy joggers and 3,950 non-joggers, ages 20 to 93, for 12 years and found that 28 of the joggers and 128 of the non-joggers died. The authors said that "The dose of running that was most favorable for reducing mortality was jogging 1 to 1.4 hours per week, with no more than three running days per week, at a slow or average pace." They defined a slow or average running pace as 5 mph, or 12-minute miles, which is incredibly slow for young people. Problems with the study include:
* It did not report whether the subjects participated in other forms of exercise besides running.
* Study participants self-reported their running, and runners often lie about their pace and distance.
* Only 127 of almost 1100 joggers were not slow joggers. This is too small a percentage to calculate death risk.
* The number of "fast" runners in this study was only 80 men and women, too small to be very statistically significant.
* Only 28 joggers and 128 non-joggers in the study died. These small numbers do not come to statistical significance to separate runners by jogging speed.
* There is no analysis of the causes of death, so we don’t even know what killed them.
* Joggers in the study were younger, had lower blood pressure and body mass index and a lower prevalence of smoking compared to the non-joggers.
Studies That Disagree with This Study
* Fast walkers tend to live longer than those who walk slowly, even if they cover the same distance (PLOS One, November 19, 2013).
* Cyclists in Denmark who ride fast regularly live longer and were less likely to die of heart attacks than those who rode slowly, even if the slow riders spent more time on the road (Eur J Prev Cardiol, 2012 Feb;19(1):73-80).
* Intensity, not the duration of cycling, is of more importance in relation to all-cause and heart attack deaths. The same authors of the most recent study conclude: "Thus our general recommendations to all adults would be that brisk cycling is preferable to slow" (Eur J Prev Cardiol, 2012 Feb;19(1):73-80). Men with fast-intensity cycling survived 5.3 years longer, and men with average intensity survived 2.9 years longer than men with slow cycling intensity. For women the figures were 3.9 and 2.2 years longer, respectively.
* The same authors showed that fast walkers live longer than slow walkers. They concluded : "Our findings indicate that the relative intensity and not the duration of walking is of most importance in relation to all-cause mortality. Thus our general recommendation to all adults would be that brisk walking is preferable to slow." (Eur J Cardiovasc Prev Rehabil, 2007 Feb;14(1):72-8).
* Small increases in exercise in inactive people have the same health benefits as much larger increases in exercise in people who already exercise (BMJ Open, 2013 Oct 18;3(10):e003509).