Bad news for the lazy – jogging isn’t actually bad for you

    6 February 2015

    There’s nothing the health editors of the nation love more than a counter-intuitive story. We’ve been over the red-wine-is-good-for-you, chocolate-is-good-for-you ones before (which tend to fall at various points on the spectrum between ‘sort of true but misleading’ and ‘downright false’). But there is the reverse kind of stories, too: the ‘exercise is actually bad for you’ ones.

    The one that did the rounds this week was the news that ‘too much’ jogging is as bad for you as not doing any exercise at all. ‘The study, which examined hours of jogging, frequency, and the individual’s perception of pace, found that strenuous joggers were as likely to die as sedentary non-joggers, while light joggers had the lowest rates of death,’ reports the Daily Mail.  The BBC and Telegraph both run the story too.

    You can see, as always, why this appeals. It’s nice for the reader to be told that those smug joggers hauling their scrawny bottoms around the local park are wasting their time, or even trotting into an early grave. The sensible thing to do, clearly, is to sit on your sofa, drinking the health-giving red wine and eating the health-giving chocolate.

    But it’s nonsense. The marvellous NHS Choices website took a look at the claims (I shouldn’t admit this, but NHS Choices should absolutely be your very first port of call for any dodgy health claims in the media). There were various limitations to the study, but the most important one was this: there were about 1,000 joggers in the study. That sounds a lot, but when you divide it up by how fast, how far, how often and so on the various joggers jogged for, you’re soon dealing with very small groups.

    ‘This was particularly the case in the most active jogging categories (those who jogged more often, for longer, and at a higher pace),’ says NHS Choices. ‘For example, there were only 36 people who were classed as “strenuous” joggers, and only two of these people died.’ The study looked at ‘all-cause mortality’ over a two-year period, so it would literally only take one of those deaths being some guy randomly getting hit by a car to double the apparent death rate.

    The study, then, is an interesting one that flags a possible area for research. But it is nowhere near statistically powerful enough to suggest that strenuous jogging is bad for you. None of the news outlets looking at the story acknowledge the weaknesses of the research: they all say things like ‘a study shows’ or ‘scientists have discovered’.

    And, of course, even if the study were absolutely true – so what? The study found that ‘1 to 2.4 h of jogging per week was associated with the lowest mortality’. The NHS recommends two and a half hours of moderate exercise a week, or 75 minutes of vigorous exercise. Moderate exercise includes walking; vigorous exercise would include jogging. So the upper end of the low-mortality range, the people running for 2.4 hours a week, are already doing almost double the recommended amount of vigorous exercise. People doing more than that are not ordinary park joggers.

    As always, the headline (‘too much jogging is bad for you!’, as though too much of anything, almost by definition, isn’t bad for you) is undermined immediately, both by the fact that the study isn’t anywhere near big enough to support the claims, and by the fact that the claims it makes are less sensational than the headline implies. And, as always, the worry is that someone will read the stupid headlines, and say ‘Well, better not go for that jog, it’s too dangerous. Better stick to the red wine and chocolate. Doctor’s orders.’