Lessons we need to learn from a Lancet Psychiatry study of the association between exercise and mental health

The closer we look at a heavily promoted study of exercise and mental health, the more its flaws become obvious. There is little support for the most basic claims being made – despite the authors marshaling enormous attention to the study.

giphyThe closer we look at a heavily promoted study of exercise and mental health, the more its flaws become obvious. There is little support for the most basic claims being made – despite the authors marshaling enormous attention to the study.

Apparently, the editor of Lancet Psychiatry and reviewers did not give the study a close look before it was accepted.

The article was used to raise funds for a startup company in which one of the authors was heavily invested. This was disclosed, but doesn’t let the authors off the hook for promoting a seriously flawed study. Nor should the editor of Lancet Psychiatry or reviewers escape criticism, nor the large number of people on Twitter who thoughtlessly retweeted and “liked” a series of tweets from the last author of the study.

This blog post is intended to raise consciousness about bad science appearing in prestigious journals and to allow citizen scientists to evaluate their own critical thinking skills in terms of their ability to detect misleading and exaggerated claims.

1.Sometimes a disclosure of extensive conflicts of interest alerts us not to pay serious attention to a study. Instead, we should question why the study got published in a prestigious peer-reviewed journal when it had such an obvious risk of bias.

2.We need citizen scientists with critical thinking skills to identify such promotional efforts and alert others in their social network that hype and hokum are being delivered.

3.We need to stand up to authors who use scientific papers for commercial purposes, especially when they troll critics.

Read on and you will see what a skeptical look at the paper and its promotion revealed.

  • The study failed to capitalize on the potential of multiple years of data for developing and evaluating statistical models. Bigger is not necessarily better. Combining multiple years of data was wasteful and served only the purpose of providing the authors bragging rights and the impressive, but meaningless p-values that come from overly large samples.
  • The study relied on an unvalidated and inadequate measure of mental health that confounded recurring stressful environmental conditions in the work or home with mental health problems, even where validated measures of mental health would reveal no effects.
  • The study used an odd measure of history of mental health problems that undoubtedly exaggerated past history.
  • The study confused physical activity with (planned) exercise. Authors amplified their confusion by relying on an exceedingly odd strategy for getting estimate of how much participants exercised: Estimates of time spent in a single activity was used in analyses of total time spent exercising. All other physical activity was ignored.
  • The study made a passing acknowledgment of the problems interpreting simple associations as causal, but then went on to selectively sample the existing literature to make the case that interventions to increase exercise improve mental health.
  • Taken together, a skeptical of assessment of this article provides another demonstration that disclosure of substantial financial conflicts of interests should alert readers to a high likelihood of a hyped, inaccurately reported study.
  • The article was pay walled so that anyone interested in evaluating the authors claims for themselves had to write to the author or have access to the article through a university library site. I am waiting for the authors to reply to my requests for the supplementary tables that are needed to make full sense of their claims. In the meantime, I’ll just complain about authors with significant conflicts of interest heavily promoting studies that they hide behind paid walls.

I welcome you to  examine the author’s thread of tweets. Request the actual article from the author if you want to evaluate independently my claims. This can be great material for a masters or honors class on critical appraisal, whether in psychology or journalism.

title of article

Let me know if you think that I’ve been too hard on this study.

A thread of tweets  from the last author celebrated the success of well orchestrated publicity campaign for a new article concerning exercise and mental health in Lancet Psychiatry.

The thread started:

Our new @TheLancetPsych paper was the biggest ever study of exercise and mental health. it caused quite a stir! here’s my guided tour of the paper, highlighting some of our excitements and apprehensions along the way [thread] 1/n

And ended with pitch for the author’s do-good startup company:

Where do we go from here? Over @spring_health – our mental health startup in New York City – we’re using these findings to develop personalized exercise plans. We want to help every individual feel better—faster, and understand exactly what each patient needs the most.

I wasn’t long into the thread before my skepticism was stimulated. The fourth tweet in the thread had a figure that didn’t get any comments about how bizarre it was.

The tweet

It looks like those differences mattered. for example, people who exercised for about 45 minutes seemed to have better mental health than people who exercised for less than 30, or more than 60 minutes. — a sweet spot for mental health, perhaps?

graphs from paper

Apparently the author does not comment on an anomaly either. Housework appears to be better for mental health than a summary score of all exercise and looks equal to or better than cycling or jogging. But how did housework slip into the category “exercise”?

I begin wondering what the authors meant by “exercise” or if they’d given the definition serious consideration when constructing their key variable from the survey data.

But then that tweet was followed by another one that generated more confusion with a  graph the seemingly contradicted the figures in the last one

the type of exercise people did seems important too! People doing team sports or cycling had much better mental health than other sports. But even just walking or doing household chores was better than nothing!

Then a self-congratulatory tweet for a promotional job well done.

for sure — these findings are exciting, and it has been overwhelming to see the whole world talking openly and optimistically about mental health, and how we can help people feel better. It isn’t all plain sailing though…

The author’s next tweet revealed a serious limitation to the measure of mental health used in the study in a screenshot.

screenshot up tweet with mental health variable

The author acknowledged the potential problem, sort of:

(1b- this might not be the end of the world. In general, most peple have a reasonable understanding of their feelings, and in depressed or anxious patients self-report evaluations are highly correlated with clinician-rated evaluations. But we could be more precise in the future)

“Not the end of the world?” Since when does the author of the paper in the Lancet family of journals so casually brush off a serious methodological issue? A lot of us who have examined the validity of mental health measures would be skeptical of this dismissal  of a potentially fatal limitation.

No validation is provided for this measure. On the face of it, respondents could endorse it on basis of facing  recurring stressful situations that had no consequences for their mental health. This reflects ambiguity of the term stress for both laypersons and scientists. “Stress” could variously refer to an environmental situation, a subjective experience of stress, or an adaptational outcome. Waitstaff could consider Thursday when the chef is off, a recurrent, weekly stress. Persons with diagnosable persistent depressive disorder would presumably endorse more days than not as being a mental health challenge. But they would mean something entirely different.

The author acknowledged that the association between exercise and mental health might be bidirectional in terms of causality

adam on lots of reasons to believe relationship goes both ways.PNG

But then made a strong claim for increased exercise leading to better mental health.

exercise increases mental health.PNG

[Actually, as we will see, the evidence from randomized trials of exercise to improve mental health is modest, and entirely disappears one limits oneself to the quality studies.]

The author then runs off the rail with the claim that the benefits of exercise exceed benefits of having greater than poverty-level income.

why are we so excited.PNG

I could not resist responding.

Stop comparing adjusted correlations obtained under different circumstances as if they demonstrated what would be obtained in RCT. Don’t claim exercising would have more effect than poor people getting more money.

But I didn’t get a reply from the author.

Eventually, the author got around to plugging his startup company.

I didn’t get it. Just how did this heavy promoted study advance the science fo such  “personalized recommendation?

Important things I learned from others’ tweets about the study

I follow @BrendonStubbs on Twitter and you should too. Brendon often makes wise critical observations of studies that most everyone else is uncritically praising. But he also identifies some studies that I otherwise would miss and says very positive things about them.

He started his own thread of tweets about the study on a positive note, but then he identified a couple of critical issues.

First, he took issue with the author’s week claiming to have identified a tipping point, below which exercise is beneficial, and above which exercise could prove detrimental the mental health.

4/some interpretations are troublesome. Most confusing, are the assumptions that higher PA is associated/worsens your MH. Would we say based on cross sect data that those taking most medication/using CBT most were making their MH worse?

A postdoctoral fellow @joefirth7  seconded that concern:

I agree @BrendonStubbs: idea of high PA worsening mental health limited to observation studies. Except in rare cases of athletes overtraining, there’s no exp evidence of ‘tipping point’ effect. Cross-sect assocs of poor MH <–> higher PA likely due to multiple other factors…

Ouch! But then Brendan follows up with concerns that the measure of physical activity has not been adequately validated, noting that such self-report measures prove to be invalid.

5/ one consideration not well discussed, is self report measures of PA are hopeless (particularly in ppl w mental illness). Even those designed for population level monitoring of PA https://journals.humankinetics.com/doi/abs/10.1123/jpah.6.s1.s5 … it is also not clear if this self report PA measure has been validated?

As we will soon see, the measure used in this study is quite flawed in its conceptualization and its odd methodology of requiring participants to estimate the time spent exercising for only one activity, with 70 choices.

Next, Brandon points to a particular problem using self-reported physical activity in persons with mental disorder and gives an apt reference:

6/ related to this, self report measures of PA shown to massively overestimate PA in people with mental ill health/illness – so findings of greater PA linked with mental illness likely bi-product of over-reporting of PA in people with mental illness e.g Validity and Value of Self-reported Physical Activity and Accelerometry in People With Schizophrenia: A Population-Scale Study of the UK Biobank [ https://academic.oup.com/schizophreniabulletin/advance-article/doi/10.1093/schbul/sbx149/4563831 ]

7/ An additional point he makes: anyone working in field of PA will immediately realise there is confusion & misinterpretation about the concepts of exercise & PA in the paper, which is distracting. People have been trying to prevent this happening over 30 years

Again, Brandon provides a spot-on citation clarifying the distinction between physical activity and exercise:, Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research 

The mysterious pseudonymous Zad Chow @dailyzad called attention to a blog post they had just uploaded and let’s take a look at some of the key points.

Lessons from a blog post: Exercise, Mental Health, and Big Data

Zad Chow is quite balanced in dispensing praise and criticism of the Lancet Psychiatry paper. They noted the ambiguity of any causality in cross-sectional correlation and that investigated the literature on their own.

So what does that evidence say? Meta-analyses of randomized trials seem to find that exercise has large and positive treatment effects on mental health outcomes such as depression.

Study Name     # of Randomized Trials             Effects (SMD) + Confidence Intervals

Schuch et al. 2016       25         1.11 (95% CI, 0.79-1.43)

Gordon et al. 2018      33         0.66 (95% CI, 0.48-0.83)

Krogh et al. 2017          35         −0.66 (95% CI, -0.86, -0.46)

But, when you only pool high-quality studies, the effects become tiny.

“Restricting this analysis to the four trials that seemed less affected of bias, the effect vanished into −0.11 SMD (−0.41 to 0.18; p=0.45; GRADE: low quality).” – Krogh et al. 2017

Hmm, would you have guessed this from the Lancet Psychiatry author’s thread of tweets?

Zad Chow showed the hype and untrustworthiness of the press coverage in prestigious media with a sampling of screenshots.

zad chou screenshots of press coverage

I personally checked and don’t see that Zad Chow’s selection of press coverage was skewed. Coverage in the media all seemed to be saying the same thing. I found the distortion to continue with uncritical parroting – a.k.a. churnaling – of the claims of the Lancet Psychiatry authors in the Wall Street Journal. 

The WSJ repeated a number of the author’s claims that I’ve already thrown into question and added a curiosity:

In a secondary analysis, the researchers found that yoga and tai chi—grouped into a category called recreational sports in the original analysis—had a 22.9% reduction in poor mental-health days. (Recreational sports included everything from yoga to golf to horseback riding.)

And the NHS England totally got it wrong:

NHS getting it wrong.PNG

So, we learned that the broad category “recreational sports” covers yoga and tai chi , as well as golf and  horseback riding. This raises serious questions about the lumping and splitting of categories of physical activity in the analyses that are being reported.

I needed to access the article in order to uncover some important things 

I’m grateful for the clues that I got from Twitter, and especially Zad Chow that I used in examining the article itself.

I got hung up on the title proclaiming that the study involved 1·2 million individuals. When I checked the article, I saw that the authors use three waves of publicly available data to get that number. Having that many participants gave them no real advantage except for bragging rights and the likelihood that modest associations could be expressed in expressed in spectacular p-values, like p<2・2 × 10–16. I don’t understand why the authors didn’t conduct analyses with one-way and Qwest validate results in another.

The obligatory Research in Context box made it sound like a systematic search of the literature had been undertaken. Maybe, but the authors were highly selective in what they chose to comment upon, as seen in its contradiction by the brief review of Zad Chow. The authors would have us believe that the existing literature is quite limited and inconclusive, supporting the need for like their study.

research in context

Caveat Lector, a strong confirmation bias is likely ahead in this article.

Questions accumulated quickly as to the appropriateness of the items available from a national survey undoubtedly constructed with other purposes. Certainly these items would not have been selected if the original investigators were interested in the research question at the center of this article.

Participants self-reported a previous diagnosis of depression or depressive episode on the basis of the following question: “Has a doctor, nurse, or other health professional EVER told you that you have a depressive disorder, including depression, major depression, dysthymia, or minor depression?”

Our own work has cast serious doubt on the correspondence of reports of a history of depression in response to a brief question embedded in a larger survey with results of a structured interview in which respondents’ answers can be probed. We found that answers to such questions were more related to current distress, then to actual past diagnoses and treatment of depression. However, the survey question used in the Lancet Psychiatry study added the further ambiguity and invalidity with the added  “or minor depression.” I am not sure under what circumstances a health care professional would disclose a diagnosis of “minor depression” to a patient, but I doubt it would be in context in which the professional felt treatment was needed.

Despite the skepticism that I was developing about the usefulness of the survey data, I was unprepared for the assessment of “exercise.”

Other than your regular job, did you participate in any physical activities or exercises such as running, calisthenics, golf, gardening, or walking for exercise?” Participants who answered yes to this question were then asked: “What type of physical activity or exercise did you spend the most time doing during the past month?” A total of 75 types of exercise were represented in the sample, which were grouped manually into eight exercise categories to balance a diverse representation of exercises with the need for meaningful cell sizes (appendix).

Participants indicated the number of times per week or month that they did this exercise and the number of minutes or hours that they usually spend exercising in this way each time.

I had already been tipped off by the discussion on twitter that there would be a thorough confusion of planned exercise and mere physical activity. But now that was compounded. Why was physical activity during employment excluded? What if participants were engaged in a number of different physical activities,  like both jogging and bicycling? If so, the survey obtained data for only one of these activities, with the other excluded, and the choice could’ve been quite arbitrary as to which one the participant identified as the one to be counted.

Anyone who has ever constructed surveys would be alert to the problems posed by participants’ awareness that saying “yes” to exercising would require contemplating  75 different options, arbitrarily choosing one of them for a further question how much time the participant engaged in this activity. Unless participants were strongly motivated, then there was an incentive to simply say no, they didn’t exercise.

I suppose I could go on, but it was my judgment that any validity what the authors were claiming  had been ruled out. Like someone once said on NIH grant review panel, there are no vital signs left, let’s move on to the next item.

But let’s refocus just a bit on the overall intention of these authors. They want to use a large data set to make statements about the association between physical activity and a measure of mental health. They have used matching and statistical controls to equate participants. But that strategy effectively eliminates consideration of crucial contextual variables. Persons’ preferences and opportunities to exercise are powerfully shaped by their personal and social circumstances, including finances and competing demands on their time. Said differently, people are embedded in contexts in which a lot of statistical maneuvering has sought to eliminate.

To suggest a small number of the many complexities: how much physical activity participants get  in their  employment may be an important determinant of choices for additional activity, as well as how much time is left outside of work. If work typically involves a lot of physical exertion, people may simply be left too tired for additional planned physical activity, a.k.a. exercise, and the physical health may require it less. Environments differ greatly in terms of the opportunities and the safety of engaging in various kinds of physical activities. Team sports require other people being available. Etc., etc.

What I learned from the editorial accompanying the Lancet Psychiatry article

The brief editorial accompanying the article aroused my curiosity as to whether someone assigned to reading and commenting on this article would catch things that apparently the editor and reviewer missed.

Editorial commentators are chosen to praise, not to bury articles. There are strong social pressures to say nice things. However, this editorial leaked a number of serious concerns.


In presenting mental health as a workable, unified concept, there is a presupposition that it is possible and appropriate to combine all the various mental disorders as a single entity in pursuing this research. It is difficult to see the justification for this approach when these conditions differ greatly in their underlying causes, clinical presentation, and treatment. Dementia, substance misuse, and personality disorder, for example, are considered as distinct entities for research and clinical purposes; capturing them for study under the combined banner of mental health might not add a great deal to our understanding.

The problem here of categorisation is somewhat compounded by the repeated uncomfortable interchangeability between mental health and depression, as if these concepts were functionally equivalent, or as if other mental disorders were somewhat peripheral.


A final caution pertains to how studies approach a definition of exercise. In the current study, we see the inclusion of activities such as childcare, housework, lawn-mowing, carpentry, fishing, and yoga as forms of exercise. In other studies, these activities would be excluded for not fulfilling the definition of exercise as offered by the American College of Sports Medicine: “planned, structured and repetitive bodily movement done to improve or maintain one or more components of physical fitness.” 11 The study by Chekroud and colleagues, in its all-encompassing approach, might more accurately be considered a study in physical activity rather than exercise.

The authors were listening for a theme song with which they could promote their startup company in a very noisy data set. They thought they had a hit. I think they had noise.

The authors’ extraordinary disclosure of interests (see below this blog post) should have precluded publication of this serious flawed piece of work, either simply for reason of high likelihood of bias or because it promoted the editor and reviewers to look more carefully at the serious flaws hiding in plain sight.

Postscript: Send in the trolls.

On Twitter, Adam Chekroud announced he felt no need to respond to critics. Instead, he retweeted and “liked” trolling comments directed at critics from the twitter accounts of his brother, his mother, and even the official Twitter account of a local fried chicken joint @chickenlodge, that offered free food for retweets and suggested including Adam Chekroud’s twitter handle if you wanted to be noticed.

chicken lodge

Really, Adam, if you can’t stand the heat, don’t go near  where they are frying chicken.

The Declaration of Interests from the article.

declaration of interest 1

declaration of interest 2


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