August 8, 2018

expert reaction to physical activity linked to improved mental health

A new cross-sectional study, published in The Lancet Psychiatry, investigates the association between physical exercise and mental health in 1.2 million individuals in the USA between 2011 and 2015.

Prof Stephen Lawrie, Head of Psychiatry, University of Edinburgh, said:

“This is an impressively large study and that alone gives the results impact and plausibility, but it has to be remembered that it is an observational, cross-sectional study of self-reported measures of both activity and mental health.  That means that we cannot be sure from these results alone whether exercise is good for mental health, but the size of the study, the careful analytical approach taken by the authors and the other evidence already available makes this very likely.

“I would summarise the results as indicating that activity, and especially social and ‘mindful’ exercise, is good for mental health – but that one can do too much. Every second day for 45-60 mins might be optimal.  Certainly, the results suggest that exercising every day is associated with worse mental health.  I suspect we all know people who seem ‘addicted’ to exercise and if this starts to impact on other aspects of life – like foregoing social activities because one has to be up at the crack of dawn to run several miles – it might actually be bad for people.

“As the authors point out, the next stage is to develop ways of encouraging specific types of exercise – preferably evaluated through clinical trials – for particular populations.”

Dr Brendon Stubbs, NIHR Clinical Lecturer, King’s College London’s Institute of Psychiatry, Psychology and Neuroscience, and Head of Physiotherapy, South London and Maudsley NHS Foundation trust, said:

“There is rapidly growing interest in the potential protective effects of physical activity against poor mental health and mental illness.

“This is an important study, which replicates findings from previous multinational studies showing that physical activity (and not exercise per se) is cross-sectionally associated with better mental health.

“The finding that reporting of engaging in 120-360 minutes physical activity per week is of considerable public health importance.  The message reinforces government guidelines which recommend people should seek to achieve over 150 minutes of physical activity per week, which could include 30 minutes 5 times a week.  The good news is that lots of different types of physical activity appear to be associated with better mental health. Thus, the key message from this paper and the wider literature is that people should find a physical activity they enjoy and try and do it regularly but just getting started is key.

“The obvious strengths of the study are the large sample size and the adjustment for other important confounders such as BMI, physical health (although self-report) among others.

“The major limitation is the cross-sectional design.  People with poor mental health or a diagnosis of a mental illness such as depression are known to engage in substantially less physical activity and the authors paper may tell us that greater mental health burden is associated with less physical activity.

“Another limitation is the physical activity questionnaire relies on self-report.  These are known to be unreliable (particularly in people with poor mental health and mental illness) and this questionnaire does not appear to be validated against a robust measure of objectively measured physical activity such as an accelerometer.

“Finally, the authors measure physical activity and not physical exercise (see below footnote for definitions from seminal paper) and this misinterpretation is evident in the paper and press release.  Thus, the message from the paper should be about physical activity and not exercise.”

Footnote:

Caspersen et al 1985 Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research, Public Health Rep. Mar-Apr; 100(2): 126–131.

“Physical activity,” “exercise,” and “physical fitness” are terms that describe different concepts. However, they are often confused with one another, and the terms are sometimes used interchangeably. This paper proposes definitions to distinguish them. Physical activity is defined as any bodily movement produced by skeletal muscles that results in energy expenditure. The energy expenditure can be measured in kilocalories. Physical activity in daily life can be categorized into occupational, sports, conditioning, household, or other activities. Exercise is a subset of physical activity that is planned, structured, and repetitive and has as a final or an intermediate objective the improvement or maintenance of physical fitness.

Dr Dean Burnett, Neuroscientist and Honorary research Associate, School of Psychology, Cardiff University, said:

“The idea of there being a link between exercise and mental health is widely held, but thus far it has remained scientifically uncertain and difficult to pin down. This new study, with its impressively vast number of subjects, strongly suggests that there is a definite association between the two. Impressively extensive analyses were used to rule out many other explanations. However, the nature of the study means it’s difficult to say more than that with any real certainty.

“The authors themselves admit up front that there’s no robust way of telling which way the association goes, which is cause and which is effect (i.e. does exercise lead to better mental health, or do people with better mental health tend to exercise more because they can?), and while the press release is reassuringly measured and specific, there are a few telling details which suggest this study has many limitations. For instance, as the authors point out, the study is based on subjects self-reporting, meaning they had to accurately appraise their own mental health and exercise habits, which introduces the possibility of many subjective biases and errors.

“As well as this, the very wide definition of ‘exercise’ introduces more potential problems. Going to the gym and doing housework are very different things; one is voluntary, the other is essentially mandatory, one can be easily quantified (distance run, weight lifted etc.) and the other is far more vague and general. Drawing specific conclusions and applications from vague data is always questionable.

“More telling is the fact that people with diagnosed mental health problems (aside from depression) were excluded from the study, so any conclusions about the therapeutic application of the data are seriously constrained as a result.

“Overall, it’s a useful study, especially due to the substantial body of information contained within it and the efforts made to rule out other variables. It seems safe to say that the link between exercise and better mental health is a real and reliable one. The press release fairly and accurately points out many different interpretations of this data, but the main concern would be that those who don’t read that far into the specifics, even if they’re clinical practitioners, will see basic headlines like ‘exercise linked to mental health’ and feel more confident in encouraging (or even cajoling) those with mental health problems to exercise more. The true relationship, as the study itself repeatedly points out, is clearly far more complicated and variable, and such an approach could lead to more harm than good in the long run.”

* ‘Association between physical exercise and mental health in 1·2 million individuals in the USA between 2011 and 2015: a cross-sectional study’ by Chekroud et al. published in The Lancet Psychiatry on Wednesday 8^th August. 

Declared interests

Prof Stephen Lawrie: “In my role as Head of the NHS Research Scotland Mental Health Network, I co-ordinate several drug trials around Scotland which some may think biases me towards pharmacological interventions for mental health/illness. As a researcher primarily interested in schizophrenia, I have done some development work towards evaluating an exercise intervention for people with schizophrenia and other major mental disorders.  As a golfer, who does regular pilates, and only some swimming, I may be biased towards social and mindful activities.”

Dr Brendon Stubbs: “No conflicts of interest, no active grants, no financial ties etc.  Only declaration is I am lead author on the imminent European Psychiatric Association guidelines and position statement on physical activity for mental illness.”

Dr Dean Burnett: “I joined a gym a few months back and still resent using it.”