Exercise benefits mental health, so why is the genetic evidence so mixed?

By Hugo Francisco de SouzaReviewed by Susha Cheriyedath, M.Sc.Nov 11 2026

Does moving more really protect your brain, or does physical fitness matter more? A review of 61 genetic studies examines the connections between exercise, muscle strength, depression, and cognitive health, raising important questions about what the evidence can tell us.

Review: Physical activity, fitness, sedentary behaviour, and brain health: a systematic review of Mendelian Randomisation studies. Image Credit: JaySi / Shutterstock

In a recent systematic review published in npj Exercise Medicine and Health, the researchers evaluated evidence for potential causal relationships between physical activity (PA), sedentary behavior, physical fitness, and psychiatric and neurocognitive outcomes.

Scientists from Amsterdam University Medical Center, the Amsterdam Public Health and Amsterdam Neuroscience research institutes in the Netherlands, conducted the research in collaboration with the University of Manchester and Greater Manchester Mental Health NHS Foundation Trust in the United Kingdom.

The researchers synthesized the findings of 61 Mendelian Randomization (MR) studies to assess whether genetically predicted differences in activity, sedentary behavior, and fitness influence participants' overall “brain health”.

Across the included studies, causal evidence linking general physical activity to improved brain health currently remains limited and mixed, with roughly half of the evaluated investigations (30 of 61) reporting exclusively null or directionally opposite outcomes.

Encouragingly, the evidence was more consistent for associations between structured aerobic exercise and lower depression risk, and between muscular strength and muscle mass and favorable mental health and cognitive outcomes. These findings do not establish that exercise interventions produce those effects.

Background

“Brain health” is an umbrella term encompassing mental well-being, psychiatric outcomes, and cognitive function. Previous reviews and public health reports focused on brain health highlight that these conditions represent a significant global burden, with mental disorders estimated to affect nearly 30% of individuals across the lifespan.

Decades of research have aimed to identify risk factors and modifiable behaviors that could be addressed to mitigate declines in brain health. Traditionally, observational epidemiology has linked physical activity to better mental health, and US and UK guidelines recommend at least 150 minutes of moderate-to-vigorous physical activity per week to reduce the risk of depression. The World Health Organization (WHO) separately recommends regular exercise to support cognitive health.

Researchers have raised concerns that observational studies may be vulnerable to residual confounding (including unmeasured socioeconomic factors) and reverse causation, wherein healthier individuals may exercise more. Previous reviews also report that while randomized controlled trials (RCTs) show short-term improvements, whether habitual physical activity exerts lifelong protective causal effects remains uncertain.

About the review

Researchers sought to address this knowledge gap and to inform future lifestyle psychiatry research and recommendations by systematically evaluating genetically informed studies of potential causal relationships between physical activity and psychiatric and cognitive outcomes. They identified relevant publications using a custom keyword search of PubMed and the medRxiv preprint server, yielding 1,130 records and 1,114 unique articles after duplicate removal.

Title, abstract, and full-text screening identified 61 eligible Mendelian Randomization studies for qualitative synthesis. Mendelian Randomization uses inherited genetic variants, commonly single-nucleotide polymorphisms (SNPs), as proxies for physical activity and other characteristics to investigate possible causal relationships. The method can reduce bias from environmental confounding and reverse causation when its genetic assumptions are satisfied.

The quality of the included publications was assessed using phenotype measurement, sample size, instrument strength, and study-specific sensitivity methods.

Researchers assessed three exposure categories: 1. Physical activity (encompassing self-reported questionnaires and device-measured accelerometers), 2. Sedentary behaviors (e.g., television viewing, computer use, and napping), and 3. Physical fitness phenotypes (assessed through measures including handgrip strength, appendicular lean mass [ALM], and walking pace).

The review's primary endpoints comprised metrics and outcomes pertaining to major depressive disorder (MDD), anxiety disorders, schizophrenia, bipolar disorder, Alzheimer’s disease (AD), and participants’ overall cognitive performance.

Review findings

Overall, strong genetic evidence for general physical activity was sparse, with almost half (30 of the 61 included studies) reporting solely null or directionally opposite findings for brain health endpoints.

Quality assessments showed that 52% of studies (32 of 61) exhibited low methodological quality, with only 11% demonstrating sufficiently strong genetic instruments. The authors cited lenient genetic variant selection thresholds, small numbers of variants, or incomplete instrument statistics as common weaknesses. Only 26 of the 61 studies used independent genetic summary statistics for a given exposure-outcome pair, meaning some apparently consistent results may reflect repeated analyses of the same datasets rather than independent confirmation.

Specific activity types showed different association patterns with brain health. For example, aerobic exercise (such as swimming and cycling) was linked to lower depression risk across all three studies evaluating this activity type, but these genetic findings do not directly establish the benefits of an exercise program.

Physical fitness phenotypes showed greater consistency than total activity volume, with potentially protective mental health associations in six of eight studies and favorable cognitive outcomes in nine of twelve studies. Several studies linked greater handgrip strength and greater appendicular lean mass to reduced depression risk and better cognitive performance. These measures may also reflect age-related frailty and underlying health conditions, complicating their interpretation as independent protective factors.

Evidence for sedentary behaviors was mixed, but prolonged television viewing was repeatedly associated with increased depression risk, and several estimates weakened after adjusting for body mass index (BMI). Socioeconomic and genetic factors could also influence these associations.

Conclusions

Taken together, the evidence suggests that physical fitness traits show more consistent protective associations with mental and cognitive health, while aerobic exercise may be linked to reduced depression risk. Current genetic evidence does not establish that routine physical activity uniformly prevents psychiatric disorders.

The authors recommend triangulating evidence by combining genetically informed designs with randomized trials and family-based cohorts to develop reliable clinical guidance for supporting lifelong brain health. The absence of clear genetic associations does not rule out benefits from physical activity that genetic studies may fail to capture.