Association Between Physical Activity and Risk of Depression: A Systematic Review and Meta-Analysis

Key Points

• Self-reported physical activity is inversely associated with risk of developing depression—no big surprise.
• But the surprise is, it doesn’t take even reaching the WHO-recommended “dose” of 30 minutes 5 times a week if this relationship is causal; half of that yields most of the benefit.
• How much are you getting?

Is exercise so obviously beneficial that you needn't bother with a meta-analysis? Well, the connection between exercise and mood may be, but there's more here. After all, this article by Matthew Pierce and colleagues recently appeared in JAMA Psychiatry, pretty much the premier research journal in our field. So, there must be more in here than, “Yeah, exercise is good for depression.” Let's see what that is.

Hi! Jim Phelps here for the Psychopharmacology Institute. The target for Pierce et al.'s analysis is: How much is enough to see mood benefit? And is more better? How much more? To address those questions, they identified 15 cohort studies that had quantified physical activity and then prospectively monitored the incidence of depression. Notice here that we're looking at the effect of exercise as prevention for depression. The follow-up duration in these cohorts was at least 3 years and some of them much longer. The Copenhagen City Heart Study, for example, was up to 26 years. The total sample across the 15 cohorts was 190,000 participants. Physical activity was reported differently in these cohorts so the authors converted all of the exercise data into METs. That's an acronym for the energy expended above the resting metabolic rate. For example, the World Health Organization recommends engaging in at least moderate intensity activity for 30 minutes, 5 times a week, which comes out to about 8.8 METs per week. Regular vigorous activity might get you up to 17 METs per week.

So, keeping in mind that range—8.8 being moderate and 17 being vigorous —the authors constructed a curve of depression incidents relative to METs per week. Compared with a completely sedentary lifestyle, those exerting 4.4 METs per week—about half of the WHO's recommended level—had an 18% lower likelihood of developing depression than those reporting nothing beyond basal metabolic rate for a week. Those reporting 8.8 METs—the WHO recommendation—had a 25% lower likelihood of developing depression over the course of the cohort study. From there, though, 8.8 METs at 25% lower likelihood, the curve of benefit relative to exertion, becomes quite flat. Now, the authors point out that the results at high levels of weekly exertion were uncertain because there were fewer cohort members exercising at those levels. Nevertheless, it appears that going beyond 8.8 METs per week—that's 30 minutes of moderate exercise 5 times a week—had no significant impact on the risk of developing depression. There is a ceiling effect here in terms of weekly intensity and duration.

Of course, the big problem with these data is so-called reverse causation. Maybe the lower incidence of depression amongst the more physically active is because depression lowers activity, not the other way around. But as Pierce et al. point out, habitual exercise was assessed at the outset of these cohort studies and then depression was counted when it began later. The long duration of follow-up, from 3–25 years, also argues really strongly against reverse causation when depression shows up much later and you can quantify exercise long before that. Another concern was that most of the participants probably didn't exercise at just the same level of intensity over all the years of follow-up. So, the observed connection between activity and risk of depression could've been stronger if the studies had repeated their assessments of exercise levels. The authors note that the cohorts were initiated in high-income countries, including 6 in the United States, with the exception of 1 that recruited participants from India, Ghana, Mexico, and Russia. So, perhaps the results could be quite different with a more ethnically and geographically diverse sample.

Two more items of interest here. First, at study entry, what percentage of the cohort population do you think was actually getting the WHO recommended level of physical activity? I'll give you 2 hints. First, except for a few people and 2 of the 15 cohorts, enrollees weren't depressed at the outset of these cohort studies. Second, what level of physical activity would you report yourself to be getting currently? Wouldn't you kind of fudge it toward the highest plausible number of hours or minutes per week? Well, even taking that into account, only 20% of the cohort participants reported exercising at the WHO-recommended level of 30 minutes a day, 5 days a week. How about 5 hours a week? That would be at a vigorous level of 17 METs. Only 5% reported that level of activity. Finally, the authors offer brief speculation about the possible mechanisms through which physical activity might account for the observed inverse association with incident depression. They invoke potential activation of endocrine and anti-inflammatory pathways and long-term changes in neural architecture. I'm telling you this because they cite a review by Kandola and colleagues, which I've included in the references because it's a detailed, thoughtful review of the possible mechanism behind the connection between exercise and depression prevention. The authors conclude that substantial mental health benefits could be achieved with physical activity levels even below the public health recommendations, with additional benefit for meeting the minimum recommended target but limited extra benefit beyond that.

For more on this, jump into that review by Kandola et al, which is linked here at the Psychopharmacology Institute. Even just skimming the topic headings could help organize your thinking about the connection between exercise and mood.

Abstract

Importance: Depression is the leading cause of mental health-related disease burden and may be reduced by physical activity, but the dose-response relationship between activity and depression is uncertain.

Objective: To systematically review and meta-analyze the dose-response association between physical activity and incident depression from published prospective studies of adults.

Data sources: PubMed, SCOPUS, Web of Science, PsycINFO, and the reference lists of systematic reviews retrieved by a systematic search up to December 11, 2020, with no language limits. The date of the search was November 12, 2020.

Study selection: We included prospective cohort studies reporting physical activity at 3 or more exposure levels and risk estimates for depression with 3000 or more adults and 3 years or longer of follow-up.

Data extraction and synthesis: Data extraction was completed independently by 2 extractors and cross-checked for errors. A 2-stage random-effects dose-response meta-analysis was used to synthesize data. Study-specific associations were estimated using generalized least-squares regression and the pooled association was estimated by combining the study-specific coefficients using restricted maximum likelihood.

Main outcomes and measures: The outcome of interest was depression, including (1) presence of major depressive disorder indicated by self-report of physician diagnosis, registry data, or diagnostic interviews and (2) elevated depressive symptoms established using validated cutoffs for a depressive screening instrument.

Results: Fifteen studies comprising 191 130 participants and 2 110 588 person-years were included. An inverse curvilinear dose-response association between physical activity and depression was observed, with steeper association gradients at lower activity volumes; heterogeneity was large and significant (I2 = 74%; P < .001). Relative to adults not reporting any activity, those accumulating half the recommended volume of physical activity (4.4 marginal metabolic equivalent task hours per week [mMET-h/wk]) had 18% (95% CI, 13%-23%) lower risk of depression. Adults accumulating the recommended volume of 8.8 mMET hours per week had 25% (95% CI, 18%-32%) lower risk with diminishing potential benefits and higher uncertainty observed beyond that exposure level. There were diminishing additional potential benefits and greater uncertainty at higher volumes of physical activity. Based on an estimate of exposure prevalences among included cohorts, if less active adults had achieved the current physical activity recommendations, 11.5% (95% CI, 7.7%-15.4%) of depression cases could have been prevented.

Conclusions and relevance: This systematic review and meta-analysis of associations between physical activity and depression suggests significant mental health benefits from being physically active, even at levels below the public health recommendations. Health practitioners should therefore encourage any increase in physical activity to improve mental health.

Reference

Pearce, M., Garcia, L., Abbas, A., Strain, T., Schuch, F. B., Golubic, R., Kelly, P., Khan, S., Utukuri, M., Laird, Y., Mok, A., Smith, A., Tainio, M., Brage, S., & Woodcock, J. (2022). Association between physical activity and risk of depression: A systematic review and meta-analysis. JAMA Psychiatry, 79(6), 550–559.

Association Between Physical Activity and Risk of Depression: A Systematic Review and Meta-Analysis