Saturday 23 November 2013

Too much running will kill you, just as sure as none at all (or so the Telegraph says anyway...)

Once again, we see another worrying study indicating that "running is bad for you". In this case, it is a story in the Telegraph with the title "Too much exercise as bad as too little". Ignoring for a moment the syntactic tautological verisimilitude of this statement, is there anything to this claim? Or is it a case of the media leaping on a piece of research and blowing it out of all proportions for a good byline?

The paper in question is this study in the journal Archive of Disease in Children, titled "Weekly sport practice and adolescent well-being". The study took a cohort of 1,245 adolescents (aged 16-20) and asked them to fill in an online survey asking them various questions about their exercise habits, socio-economic background, height, weight, and questions on their "well-being" (more on exactly what this means in a second). They split the individuals up into a number of groups based on whether they took part in:
  • A low amount of weekly sport (0-3.5 hours)

  • An average amount of weekly sport - the recommended 7 hours (3.6 - 10.5 hours)

  • A high amount of weekly sport - around double the recommended (10.6 - 17.5 hours)

  • A very high amount of weekly sport (> 17.5 hours)
They then show that, when compared against the recommended amount, doing a higher level of sport resulted in individuals being "healthier", whilst doing less resulted in individuals being "unhealthier" (as you might expect). However, when they did the same for those individuals who did a very high amount of weekly sport, they found that they were in fact "unhealthier". So not only are there diminishing returns to your health by increasing the amount of exercise that you do, but doing too much can actually result in a negative effect on your health. Hence the tag line of "too much exercise as bad as too little".

So this seems to be another paper indicating that overdoing training is actually deleterious to our health, which is particularly applicable to us idiots who might run more than 17.5 hours in a single session. But what is "too much exercise"? Sure for someone who has never run before doing a marathon right off the bat is probably not a great idea. But if you have been training for years and built your body up gradually then it is no problem at all. Too much is obviously bad as it is - by definition - more than you should be doing. But that level is going to be different for different people.

Now don't get me wrong, I have no doubt that what we do in particular isn't necessarily healthy, but that's really more from a musculo-skeletal point of view than a cardio-vascular or mental one. I'm yet to be convinced by all of these studies that actually show that doing more than X hours of exercise will cause my heart to explode. I've already made my feelings on some of these studies clear. It's not like I do this for any kind of health benefits anyway - it's just a nice added bonus that it makes me feel great!

So what are we to make of this paper? Should we be worried? Well first of all I would ask a very important question about this study - what do they mean by "healthy"? The way that the newspaper article is written makes it sound like they measured the individual's health in terms of things like blood pressure, cholesterol levels, heart rate, VO2 max, cytokine levels, general fitness, weight or BMI, or any one of myriad measures that one might associate with overall "health". Instead, the study was more focused on well-being, a more esoteric idea of how an individual feels, that is more related to mental health than to physical health. The measure that they used was the results of the WHO-5 Well Being test - a series of 5 questions asking you to score the following 5 statements based upon how they have applied to you over the previous 2 weeks - from 0 (at no time) to 5 (all of the time):
  1. I have felt cheerful and in good spirits

  2. I have felt calm and relaxed

  3. I have felt active and vigorous

  4. I woke up feeling fresh and rested

  5. My daily life has been filled with things that interest me
A score less than 13 (out of a maximum of 25) is classified as being indicative of poor well-being. Now I don't know about you, but I find this selection of questions a little odd as a way of determining the effect of exercise on health. Psychology is most definitely not my field, but it all just seems a little... I dunno. Hippy dippy? I mean, I'm pretty sure that I have pretty good well-being, but I also have a 9 month old who doesn't sleep more than 2 hours at a time. I can't say that I come off too well in this test! But compared to the fact that I am fitter and stronger than I have ever been, and extremely happy with my life (although a bit more uninterrupted sleep maybe wouldn't go amiss), I think that saying that I have poor well-being is a bit much.

I can also see many correlative factors that don't seem to be taken into account here. For one thing, I would imagine that one big difference between the group of adolescents in the very high exercise group compared to those in the high is that it likely contains a higher proportion of more elite athletes - i.e. athletes who are regularly competing. Inevitably this brings with it a level of stress that will not be felt by someone just exercising for fun or to keep fit.

Another problem is that it does not take into account the nature of the exercise. Is that 17+ hours of walking or 17+ miles of high intensity sprint intervals? I would wager that the people in the very high exercise group are likely also working much harder (which is going to have an effect on how active and vigorous you feel).

What we have here is a correlation between the amount of exercise and the levels of well-being, but what is not obvious is what the causality is. Are people who exercise more stressed? Or are stressed people more likely to do more exercise (many people, particularly runners, see exercise as a cathartic escape from the stress of daily life)? Or is it just that the sort of people more likely to have the inclination to train more are also more likely to experience stress because of it (i.e. athletes training to compete). The authors do acknowledge this point, although only after suggesting that their findings should be used in the clinical setting to:

"inform patients of this association: adolescents practising sport in accordance to once or twice the recommended duration have shown higher levels of well-being. In contrast, those practising lower or higher duration have shown poor well-being."
There are also a few problems with the study design which might result in bias in the data. For instance, the number of people in the very high exercise group was low compared to the other groups (60 individuals, or 4.8%), so these results are based on a relatively low cohort. Also, the sample was not randomly selected as it required recruitment from sports centres, websites, social networking etc. And since the results were self-reported there may be some bias there as well. Again, these limitations are discussed and acknowledged by the authors, and realistically no study is perfect.

Overall I think that it is an interesting study, but I'm not sure that it speaks to an overarching health concern. To me it suggests that people who train more can get more knackered! I feel like that sometimes, but generally I love the way that running makes me feel. I also never resent running - it is never a chore that I have to do, but is something that I do purely for fun. As soon as it stops being fun I will stop.

But one thing that jumps right out at me in this paper is Figure 1. This shows the mean well-being scores for the different groups, and the thing that jumps out at me is this simple fact - the mean well-being score for the very high group is actually very similar to that of the average group. And that is despite the fact that we know that almost 20% of these individuals have a score less than 13 - more so than in the other group. So this must mean that the other 80% actually have very good well-being scores. So perhaps exercising more is in fact better for your well-being, but this group is also more likely to contain individuals suffering more stress (for one if the reasons discussed previously)? Who knows. The point is that it is a bit early to draw any firm conclusions.
Figure 1 from Merglen et al (2013) Weekly sport practice and adolescent well-being, Archives of Disease in Childhood.
As ever, for every story which shows that exercising too much is bad for you there is a story showing that it is good for you. This story looks at a study comparing the survival rates of over 15,000 Olympic medal-winning athletes with matched normal individuals (i.e. they paired each athlete with a normal person with the same sex, age, etc.). The source paper can be found here. It shows that, when you look at death rates in the 30 years following the year the medal was won, the Olympic medalists showed a survival advantage of nearly 3 years. Interestingly athletes involved in endurance sports showed a bigger survival advantage than those doing power sports such as weight lifting. There are several possible explanations for this, including genetic factors, improved diet, the "wealth and status that come with international sporting glory" (although I wonder how many of these athletes actually saw much in the way of wealth?), and increased physical activity. So sure, they may have lower well-being according to the WHO-5 scale, but they are clearly still healthier. 

Of course bear in mind that this study itself likely has its own flaws, so should also be taken with a pinch of salt. My point is mainly that the situation is more complex than the media would have you believe. 

Case in point is a story in the Daily Mail yesterday (I refuse to link to it) that boldly claims that "90% of obese people could have mutation that means they're programmed to eat more and move less". The paper that they are referring to is this recent study in the American Journal of Human Genetics that identifies a mutation in the gene cep19 that seems to be associated with obesity. The paper itself is very cool. They took a large family of 44 individuals and split them up into those that were affected (13) or unaffected (31) by obesity based on their BMI. Now one point to make is that actually the entire family had very high BMIs, so the controls were not exactly "normal". But essentially this mutation was detected in all 13 affected individuals, but not in the unaffected. When they went on to knock the gene down in mice, they found that the mice became very obese as they seemed to just eat more. So somehow this mutation seems linked to appetite suppression (although given it's known role its not exactly obvious how the pathology works. But hey, that's another story!). 

So this is a very interesting finding indicating that there may be some genetic component to obesity (unsurprisingly in my opinion). But this particularly mutation isn't one that makes you fat. It just affects the way your body signals to you that you are full, so self-control is needed. And where in the hell did the Daily Mail get this "90% of obese people have it" quote from? In this study, only 13 out of about 25 of the family members that would be classed as "clinically obese" (i.e. BMI >= 30) have the mutation. And this is in a single family (genetics tends to be relatively similar between family members y'know) that was pre-selected based on their high weight. I doubt this is more prevalent in the population at large.

Oh yeah, and this mutation makes you infertile. So yeah, probably not that prevalent at all really. 

One of the big problems is that people want a quick fix. They want to be told that their problem is not their fault - it is their genes, so what can they possibly do about it? And hey, if it's their genes then there is probably a pill they can take to make them thin right? Unfortunately it's just not that easy. Nothing good comes for free, and if you want to look like a runway model (although why the hell would you) it's not going to happen without some effort on your part. 

We see the same sort of "easy fix", "silver bullet" approach to running. People are always looking for something to help them improve their PB without any work. James Adams wrote a great blog post (somewhat superseding a post I was working on) about the kind of quick fixes that people look for when trying to improve their running. 

But hey, if you're really serious about improving your PBs, forget about magnet bracelets, Kinesio tape, beetroot juice and the Paleo diet. The real key is to chop your foreskin off. What can I say, sometimes it takes true dedication to see real results. 

Failing that of course, you could always try the old (but somehow forgotten) technique of getting out there, training harder, and trying to run faster. It's your call.

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