There have been headlines the media in the last week reporting on research that concluded there may be an upper limit to the level of exercise that should be considered “safe”. The Danish study looked at 1,098 healthy joggers and 3,950 healthy non-joggers over a period of 12 years. The joggers were classified as “light”, “moderate” or “strenuous”, and grouped according to frequency and quantity of jogging. The groups were compared by rates of mortality (of any cause) over the period of the study. The researchers concluded that light and moderate-paced joggers, who jogged between one hour and two and a half hours a week had a lower rate of mortality, whereas strenuous joggers had a similar mortality rate to non-joggers.
So, if you’ve just signed up for a marathon and are training hard, what does this mean for you? Well, frankly, don’t panic. It’s an interesting study, and further research might help clarify what’s happening – but there’s nothing here that should stop the keen runner. In the Danish study, the group size for the “strenuous joggers” was very small – only 36. Of these 36, two people died over the 12-year study period. And remember, the study looked at “all-cause mortality”. These people may have died in road accidents, or of infectious disease – there’s no suggestion here that the jogging was in any way causal. The study highlights a pattern linking exercise level and mortality; but the numbers are just too small to draw any conclusions.
Some media outlets have reported on the “warning” lesson of the death of Jim Fixx, the keen runner who is credited with kick-starting a running revolution. He died of a heart attack whilst out on his daily run, at age 52, in 1984. They didn’t mention that there was a family history of heart disease (Jim’s father had died of a heart attack age 43), that he had been a heavy smoker up until the age of 35, and that, despite his svelte looks, his friends talked of his less-than-healthy diet. If he hadn’t been a keen runner, perhaps he would have died sooner? Unsurprisingly, there’s no single solution to looking after ourselves – we need to eat well and exercise to be healthy.
The statistic less reported from the Danish study is that, of the 394 people in the “sedentary” group, 120 died. That’s over 30% (as opposed to the less-than-6% deaths in the “strenuous” group). The message that should be jumping out here is the one we already know – inactivity is the big problem. It’s estimated that the cost of physical inactivity to the country is £7.4 billion a year. Public Health England are running a big campaign to encourage people off their chairs, get out, get fitter, slimmer, lower their risk of diabetes, cancers, heart disease… So if the question is “to exercise or not to exercise?”… I think the answer’s clear.
Dose of Jogging and Long-Term Mortality Journal of the American College of Cardiology Vol 65 Issue 5
Stop that binge jogging! Daily Mail article 2 Feb 2015
Strenuous jogging “as bad as no exercise” claim NHS online article published 3 Feb 2015
Everyone Active, Every Day Public Health England campaign