Summary: New research strengthens evidence that higher levels of physical activity lower the risk of developing depression. The study found objectively measured activity reduced depression risk even in people with genetic vulnerability to depressive disorders.
Source: Mass General
Background
Many observational studies report an association between greater physical activity and lower rates of depression, but the direction of that relationship has been uncertain: does physical activity protect against depression, or does depression lead people to become less active? Researchers from Massachusetts General Hospital (MGH) applied a genetically informed approach to address this question and provide strong support for physical activity as a preventive measure against depression. Their report was published in JAMA Psychiatry.
Lead author Karmel Choi, PhD, of the Psychiatric and Neurodevelopmental Genetics Unit in the MGH Center for Genomic Medicine, explained: “Using genetic data, we found evidence that higher levels of physical activity may causally reduce risk for depression. Knowing whether an associated factor actually causes an outcome is important because we want to invest in preventive strategies that really work.”
Methods: Mendelian randomization and objective activity measurement
The team used Mendelian randomization (MR), a method that leverages genetic variants as natural experiments to estimate causal effects of a non-genetic exposure on an outcome. Because gene variants are inherited randomly across populations, they can act as less biased proxies for lifetime differences in traits such as physical activity and help distinguish causal directionality: whether activity influences depression, depression influences activity, or both.
For genetic instruments the researchers drew on large-scale genome-wide association studies (GWAS). Physical activity GWAS came from the UK Biobank and included two measures: self-reported activity from approximately 377,000 participants, and objective measures from wrist-worn accelerometers for about 91,000 participants. The GWAS for major depressive disorder (MDD) used data from more than 143,000 participants with and without the condition.
Key findings
The MR analyses indicated that accelerometer-measured physical activity—but not self-reported activity—was causally associated with a lower risk of depression. Specifically, a 1-standard-deviation increase in mean acceleration (the accelerometer measure) corresponded to an estimated 26% lower odds of MDD (OR = 0.74; 95% CI, 0.59–0.92; P = .006). In contrast, there was no evidence that genetic liability to MDD causally reduced accelerometer-measured activity, and no significant causal relationships were identified between self-reported activity and MDD in either direction.
The discrepancy between objective and self-reported measures likely reflects limitations of self-report, such as imperfect recall or social desirability, and the inability of questionnaires to capture incidental movement—walking to transit, climbing stairs, household tasks—that accelerometers record.
Choi summarized the practical takeaway: “On average, doing more physical activity appears to protect against developing depression. Any activity is better than none. Our rough calculations suggest that replacing sitting with about 15 minutes of vigorous, heart-pumping activity like running, or about an hour of moderately vigorous activity, produces an average increase in accelerometer-measured activity that was linked to lower depression risk.”
Senior author Jordan Smoller, MD, ScD, director of the Psychiatric and Neurodevelopmental Genetics Unit and professor of Psychiatry at Harvard Medical School, noted the value of MR: “Gene variants do not determine a person’s behavior or destiny, but their average associations with traits in very large studies can help answer whether a tendency to engage in more physical activity has a likely causal effect on depression. Those answers can guide the design of clinical trials and prevention strategies.”
Implications and future directions
The study highlights two important implications for research and public health. First, objective measurement of physical activity is crucial in epidemiologic studies of mental health, because accelerometer data captured a protective effect that self-reports did not. Second, the findings support the hypothesis that increasing physical activity could be an effective prevention strategy against depression. However, translating this knowledge into action requires more research on how best to promote sustained activity across diverse groups, including people with genetic vulnerability to depression or those under considerable stress.
Choi emphasized ongoing work: “We are now exploring whether and how much physical activity benefits different at-risk groups, to better tailor recommendations and promote resilience to depression.”
Additional co-authors of the JAMA Psychiatry report include Chia-Yen Chen, PhD; Murray Stein, MD, MPH; Karestan Koenen, PhD; Min-Jung Wang, MSc; and Yann Klimentidis, PhD. Funding and support for the study included National Institute of Mental Health grants T32 MH017119 and K24 MH094614, as well as support from private foundations and institutional research funding.
Abstract (condensed)
Importance: Growing evidence links physical activity to lower depression risk, but causality and direction remain unclear.
Objective: To examine bidirectional relationships between physical activity and depression using Mendelian randomization with genetic instruments derived from large GWAS of objective and self-reported activity and of major depressive disorder.
Design and participants: Two-sample MR analyses used genetic variants associated with self-reported activity (n ≈ 377,234), accelerometer-based activity (n ≈ 91,084), and MDD (n ≈ 143,265) from large, nonoverlapping GWAS in adults of European ancestry.
Results: MR evidence supports a protective relationship between objectively measured physical activity and MDD (OR 0.74 per 1-SD increase in mean acceleration). There was no evidence of a causal effect from MDD to accelerometer-measured activity, nor were there significant causal effects involving self-reported activity.
Conclusions: Robust genetic-instrument evidence supports that objectively assessed physical activity reduces the risk of major depression. These findings underscore the importance of objective activity measurement in mental health research and support the potential of activity promotion as a prevention strategy for depression.