I guess I’m biased against the idea that exercise is very important for health. I hated sports as a kid, and efforts at getting “fit” as an adult have generally ended in failure within months. Speaking of the word “fit”, one of my favourite quotes from Terry Pratchett’s discworld novels is this little exchange, from the book “Moving Pictures”:
‘That would be the senior masters, Master,’ said the Bursar. ‘I would say they are supremely fit, myself.’
‘Fit? The Dean looks like a man who’s swallered a bed!’
‘Ah, but Master,’ said the Bursar smiling indulgently,‘the word ‘fit’, as I understand it, means ‘appropriate to a purpose,’ and I would say the body of the Dean is supremely appropriate to the purpose of sitting around all day and eating big heavy meals.’
Yes, while other kids were kicking a ball around outside, I was safely ensconced in bed reading Discworld novels. I guess that puts me at odds with other doctors with an interest in health optimization, such as Peter Attia and Shawn Baker, who were more or less professional athletes long before they ever started studying medicine, and who are therefore clearly biased in the opposite direction.
I’ve written previously about how exercise is not a particularly effective way to lose weight, and about how vigorous exercise will not make you live longer than if you stick with moderate exercise, such as walking – in fact, 10,000 steps of moderate intensity walking per day is all you need, if the goal is to maximize longevity. Which suits me just fine, because that’s about as much exercise as I can bring myself to do.
But there could be other benefits associated with exercise. Elderly people who suffer from sarcopenia (muscle wasting) clearly benefit from strength training as a means to maintain functional independence for as long as possible, as do people with osteoporosis (a weak and fracture-prone skeleton). It has also frequently been claimed that exercise improves cognitive function. That claim has however up to now been based more on wishful thinking than on any actual evidence.
A systematic review carried out by the Cochrane Collaboration in 2015 failed to show any benefits of aerobic exercise on cognitive function, but that review was limited by the fact that all the included trials were small and short term – in other words the data was statistically underpowered. Which is why it’s nice to see that a large randomized controlled trial has now been published in the American Journal of Clinical Nutrition, that sought to answer definitively the question of whether exercise improves cognitive function.
This new trial included 1,401 participants in total and they were followed for an average of four years, so if there is a meaningful difference it should be detectable. The trial was conducted in the city of Kuopio in Finland and ran from 2005 to 2011. It’s strange that it’s taken the researchers ten years to get their results published – I’ll discuss why I think that is at the end of this article.
The study wasn’t blinded, which is always a problem, because it introduces some measure of bias – the control group will tend to perform worse since they know they’re the control group, and the researchers will tend to rate them worse since they want the study to produce a positive result (positive studies get more attention and get cited more often, and are therefore more helpful for researchers from a career perspective). On the other hand, it’s hard to blind a study involving exercise interventions (maybe impossible), so it’s hard to be too critical of the lack of blinding in this type of study.
The average age of the participants was 67 years. They were randomized to one of six different groups, with roughly 230 participants in each group. The first group was a control group that was more or less left to its own devices. The second was an aerobic exercise group that was told to do 60 minutes of moderate intensity aerobic exercise five times a week. The participants in the aerobic exercise group were allowed to choose the type of exercise themselves, although they were coached in a peculiar Finnish form of exercise called “Nordic walking”, which is basically brisk walking with ski poles.
The third group was a resistance training group that was told to do at least two strength training sessions per week. While the aerobic exercise group was unmonitored during exercise, the strength training group engaged in supervised exercise at the research centre’s own gym. The fourth group was a diet group that was told to follow the standard diet recommendations that were being promulgated by the Finnish health authorites at the time:
- Eat at least four servings of fruit, vegetables and, berries per day
- Eat at least two servings of fish per week.
- Eat at least 14 gramsof dietary fibre per 1000 calories of food.
- Get at most 10% of calories from saturated fat.
nonsense message, in other words. The fifth group did both aerobic exercise and diet modification, and the sixth group that did both resistance training and diet modification. The two exercise only groups received eleven individualized face-to-face counseling sessions over the course of the four years and three group sessions, as did the diet only group. The purpose of all these sessions was to educate and motivate the participants and make sure that they kept following their prescribed interventions. The two exercise + diet groups each received twice as many counseling and group sessions – in other words 22 face-to-face sessions and six group sessions.
Obviously this is a problem. The control group basically received zero attention, the single intervention groups received some attention, and the dual intervention groups received a lot of attention. Any difference in outcomes between the groups could thus simply be due to differences in how much attention they were getting from the people conducting the study – it is a well known fact that the more attention study participants are getting, the better they will tend to perform. This is poor trial design. A properly designed trial should give equal attention to all participants, including those in the control group, so that any difference seen in outcomes isn’t just due to differences in how much attention the participants are getting.
Cognitive function was assess used using a battery of tests called CERAD. The maximum possible score on CERAD is 100, and the participants had an average score at the start of the trial of 83 out of 100. The trial has a 98% statistical power to detect a 3.5 point difference on the CERAD, which the researchers determined to be the minimum clinically meaningful difference – in other words the study had a lot of statistical power, and if there was any meaningful difference in results between the groups, the study was almost certainly going to detect it.
The participants averaged half an hour per day of moderate intensity exercise at baseline. In other words, the average participant was already doing half an hour per day of walking at normal speed at the beginning of the study. That means this study cannot say what will happen to cognitive function if you take someone who literally just lies in bed all day, and then get them to do some exercise – it tells us what will happen if you take someone who already does some walking per day (as most people do), and then get them to do more exercise. The average participant did no strength training at the beginning of the study.
When it comes to diet, the average participant already ate four servings per day of vegetables, fruits and berries and already consumed 14 grams of fibre per 1000 calories. They consumed a little bit more than the recommended amount of saturated fat (11% of total calories), and they ate less fish than recommended (45 grams compared with the recommended 250 grams). Overall, in other words, apart from a low fish consumption, the participants were already largely following the official Finnish dietary recommendations.
Let’s get to the results.
I think it’s worth stating up front that the diet intervention groups did not differ in any meaningful way in terms of what they ate at the end of the study from the other groups. That means that this study cannot say anything about effects of diet on cognitive function. It also shows how hard it is to get people to change their diets. The diet intervention groups didn’t even noticeably increase their intake of fish, even though it was very low to start with, and that would have been an easy and concrete thing to do. It makes me a little depressed to be honest – in spite of regular coaching and lots of attention from the people running the study, there was no change over the four years.
Fortunately, that’s not really what this article is about. We want to know what happened to the exercise intervention groups. These groups did noticeably change their behaviour. The aerobic exercise group increased the amount of aerobic exercise by about 47 minutes per week, which represents a 25% increase in time spent engaging in aerobic exercise. The resistance training group went from averaging 0.1 strength training sessions per week to averaging 1.3 – also a marked difference.
Unfortunately, all this effort had exactly zero impact on cognitive function. None of the five intervention groups showed an improvement in cognitive function at four years when compared with the control group. There were marginal variations between the groups but they were neither statistically significant nor clinically significant. The difference between the aerobic exercise group and the control group was 0.1 points (on the 100 point scale). The difference between the resistance training group and the control group was 0.4 points. The difference between the diet only group and the control group was 0.8 points (funny when you consider that the diet group did not actually change its diet in any noticeable way). The difference between the “resistance training + diet” group and the control group was also 0.8 points.
The biggest difference between the control group and one of the intervention groups was with the “aerobic exercise + diet” group: 1.4 points on the 100 point CERADS test. If you think that’s in any way a meaningful difference, then I would remind you that the researchers had themselves set the bar for a minimum clinically meaningful difference at 3.5 points, so a 1.4 point difference isn’t even close to being clinically significant, even if it had been statistically significant (which it wasn’t).
That marginal difference can likely be explained completely by the facts that the study was unblinded and that the intervention groups received much more attention than the control group. It certainly can’t be explained by some extra benefit seen when aerobic exercise is combined with dietary change, since there was no noticeable dietary change.
That isn’t the impression you’ll get if you read the authors’ own conclusion. They write:
The main finding of the study is that regular at least moderate-intensity aerobic exercise combined with a healthy diet … showed a trend toward improved global cognition during 4 y in middle-aged and older individuals from a general population ... These findings could be used to encourage people to increase physical activity and improve diet and for health care professionals to emphasize these lifestyle changes for the prevention of dementia.
It’s a conclusion that would be hilarious if it wasn’t so typical. They’ve taken completely negative findings and turned them in to a recommendation to exercise more and improve your diet – If your results go against the prevailing dogma, pretend like they are actually perfectly in line with it. It confirms again that you can never trust what the authors of studies write in their conclusions – you have to look at the data yourself.
This is likely the reason why it took the researchers ten years to publish their data – the study showed something different from that they wanted it to show, so they sat on it for as long as they could. When that was no longer an option, they published, but made sure to spin the results as hard as they could and hoped that nobody would notice.
What can we conclude?
Two things. First, you can’t trust what researchers claim their research shows. Second, exercise does not noticeably improve cognitive function.