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My attitude to exercise was best summed up by cartoonist Paul Terry:
When I feel like exercising, I just lie down until the feeling goes away.
However, I am not deaf to the cacophony of advisers recommending that people should keep active, particularly the over 50s. The notion seems to be that the elderly serve some undefined but useful purpose which could be prolonged by physical exertion. I find this proposition doubtful on all grounds.
Nonetheless, even morning radio programs which normally deal with high matters of State have propagated the latest finding, that the over 50s should do at least 150 minutes of exercise per week, because a recent study, a meta-analysis no less, has shown that cognitive function was better preserved in those who took exercise.
At this stage we must make a detour. Health and longevity can be predicted by the 11+ IQ test, so ideally participants in these sorts of studies should be restricted to those on whom we have early life assessments of intelligence. Of course, this is impracticable, and if the papers are on properly randomized samples, they can still detect the effects of extra exercise. However, when control is made for early life assessments of intelligence and health there is little evidence that variations in self-reported exercise have any influence on mental status in the elderly. There is certainly plentiful evidence that lower ability (as tested at 11) is associated with greater hazard ratios. That is, brighter people live longer (right hand figure), and psychologically calm persons live longer than worriers (left hand figure). It would be good if more researchers paid attention to these findings, and included even brief measures of ability and personality in their assessments.
However, we cannot ignore a good quality meta-analysis implying that exercise can mitigate the impact of ageing on cognitive function. Additionally, I warm to this paper because they have not been prissily prescriptive about what constitutes exercise. Good on them. Any stirring of the body parts is worthy of commendation.
Joseph Michael Northey, Nicolas Cherbuin, Kate Louise Pumpa, Disa Jane Smee, Ben Rattray. Exercise interventions for cognitive function in adults older than 50: a systematic review with meta-analysis. British Journal of Sports Medicine, BMJ.
Here are their methods:
The search returned 12 820 records, of which 39 studies were included in the systematic review. Analysis of 333 dependent effect sizes from 36 studies showed that physical exercise improved cognitive function (0.29; 95% CI 0.17 to 0.41; p<0.01). Interventions of aerobic exercise, resistance training, multicomponent training and tai chi, all had significant point estimates. When exercise prescription was examined, a duration of 45–60 min per session and at least moderate intensity, were associated with benefits to cognition. The results of the meta-analysis were consistent and independent of the cognitive domain tested or the cognitive status of the participants.
The effect size is respectable, equivalent to 4.4 IQ points. However, they haven’t measured intelligence, and don’t actually find that overall cognition (measured by the mini mental state assessment) is preserved by such exertions. They do pick up some very promising effects for executive functions and memory. I cannot find which tests were used, nor the length of the follow-ups in the supplementary materials.
Neuropsychological tests were classified according to the domain of cognition being assessed, similar to previous reviews. The domains considered were global cognition (eg, The Mini-Mental State Examination), attention (sustained alertness, including the ability to process information rapidly), executive function (a set of cognitive processes responsible for the initiation and monitoring of goal-orientated behaviours), memory (storage and retrieval of information) and working memory (short-term manipulation of encountered information).
The effect of exercise on cognition was statistically significant for all domains, except global cognition. As prior reviews have indicated the effects of exercise on cognition may vary depending on the mode of exercise and cognitive domain, we included both these moderators as an interaction term in a separate model. Studies of resistance training had significant interaction effects on executive function (SMD=0.49, 95% CI 0.20 to 0.78; p<0.01), memory (SMD=0.54, 95% CI 0.23 to 0.85; p<0.01) and working memory (SMD=0.49, 95% CI 0.16 to 0.82; p<0.01). There was also a significant tai chi x working memory interaction (SMD=−0.70, 95% CI −1.21 to −0.19; p=0.01). All other interaction terms were non-significant.
Here are the main results on cognition after exercise:
Tai Chi seems to do well, though the number of studies is smaller than other forms of exercise. The frequency of taking exercise shows a dose-response relationship, but less for intensity and duration and length, which is a little surprising. Moving about a bit every day seems the best policy. More socially active control groups seem almost as good as exercise, as does the sham exercise of stretching, so this is somewhat of a worry for the “exercise saves your wits” hypothesis.
The type of control group was associated with differences in the statistical significance of the effect size estimated. When the control group involved either no contact (eg, waiting list, usual care; p<0.01) or education (eg, computer course, health lectures; p=0.01) the estimate was statistically significant. Where the control condition was exposed to an active control (eg, stretching; p=0.17) or social group (p=0.62), the effect size was still positive but no longer statistically significant.
This is a quibble, but when the authors say “the effect size was still positive but no longer statistically significant” what they in fact mean is “there was no effect”.
This is a very useful meta-analysis of intervention studies. Although we do not have prior measures of ability and personality, we can hope that random allocation to experimental groups should have balanced out those factors, though volunteers in such studies tend to be brighter than average. We do not know how long the follow-ups were, nor much about the previous health and nothing about the intellectual levels of the participants. However, those without mild cognitive impairment have done better than those already mildly cognitively impaired. I would like to see which executive function and memory tests were used, but all of them are moderately correlated with general ability. Reaction times, grip strength and a process measure like digit-symbol would be very welcome additions.
In sum, an interesting paper, which might provoke some people to walk about a bit, which is no problem so long as they do not clog up the traffic.
Disclosure of competing interests: 650 metres swim each weekday morning, since you may be wondering. Pointless.