Active commuting, anxiety symptoms and mental wellbeing: a dose-response study

Technical Summary: Active Commuting, Anxiety Symptoms, and Mental Wellbeing

Problem Statement
While active commuting (walking and cycling for transportation) is well-established as a sustainable behavior with significant somatic health benefits, its relationship with mental health remains inconsistent. Previous literature reports small positive, null, or even adverse associations between active travel and mental health outcomes. Furthermore, the potential for a dose-response relationship—where higher volumes of active commuting might yield different mental health outcomes than lower volumes—remains under-explored, particularly regarding anxiety and mental wellbeing. Additionally, it is unclear whether environmental factors, specifically the perceived greenness of commuting routes, moderate these associations. From a planetary health perspective, understanding these dynamics is crucial to determining if active commuting supports both human wellbeing and environmental sustainability.

Methodology
This cross-sectional study utilized data from the "Environment and Health Survey" conducted by the Finnish Institute for Health and Welfare (THL) between June and September 2023. The survey targeted inhabitants of the ten largest cities in Finland.

• Sample: The final analytical sample consisted of 1,672 employed adults (mean age 45.3 years; 53.8% women) who were not retired, on family leave, or students, and who had commutes under 20 km. Participants with recent medication use for anxiety or depression were excluded.
• Exposure: Active commuting was defined as traveling the entire commute by walking or cycling (including e-biking). Exposure was quantified in two ways:
  1. Distance: Approximated annual km/week, derived from self-reported frequency and distance, weighted by summer (7 months) and winter (5 months) seasons.
  2. Energy Expenditure: Approximated annual MET-h/week, calculated using standard MET values (4 METs for walking/cycling) and speeds from the Compendium of Physical Activities.
• Outcomes:
  • Anxiety Symptoms: Measured using the Generalized Anxiety Disorder-7 (GAD-7) scale. A binary variable was created (minimal vs. at least mild symptoms) for primary analysis due to data skew.
  • Mental Wellbeing: Measured using the World Health Organization-Five Well-Being Index (WHO-5) as a continuous score (0–100).
• Moderator: Perceived commute greenness was assessed via a single item regarding the proportion of the route covered by green space, dichotomized into <50% vs. ≥50%.
• Statistical Analysis: The study employed logistic regression (for anxiety) and linear regression (for wellbeing) with restricted cubic splines (3 knots) to evaluate non-linear dose-response associations. Models were adjusted for age, gender, education, income satisfaction, relationship status, smoking, alcohol use, leisure-time physical activity, and occupational physical strain. Interaction terms tested whether greenness moderated the relationship.

Key Contributions

• Dose-Response Modeling: The study applied flexible dose-response modeling (restricted cubic splines) to examine non-linear associations between active commuting volume and mental health, addressing a gap in previous literature that often relied on categorical comparisons.
• Dual Metrics: Active commuting was quantified using both distance-based (km/week) and energy expenditure-based (MET-h/week) metrics, enhancing comparability with public health guidelines and tools like the WHO Health Economic Assessment Tool (HEAT).
• Greenness Moderation: The study explicitly tested whether the perceived greenness of the commuting route modifies the relationship between active commuting and mental health outcomes.
• Seasonal Consideration: The methodology accounted for seasonal variations in commuting behavior by deriving weighted annual averages based on Finnish climate conditions.

Results

• Dose-Response Associations: The study found no statistically significant dose-response relationships between active commuting (whether measured in km/week or MET-h/week) and anxiety symptoms or mental wellbeing. This null finding persisted across minimally adjusted and fully adjusted models.
• Moderation by Greenness: No effect modification was observed. The interaction terms between active commuting and commute greenness were non-significant ($P_{interactions} > 0.167$ for anxiety; $P_{interactions} > 0.123$ for wellbeing).
• Correlations: While higher active commuting correlated slightly with higher anxiety symptoms ($\rho=0.05$) and greater commuting greenness correlated with lower anxiety and better wellbeing, these correlations did not translate into significant causal or dose-response associations in the regression models.
• Sensitivity Analyses: Results remained consistent when adjusting for Body Mass Index (BMI) and when analyzing summertime commuting data separately.

Significance and Claims
The authors claim that, contrary to the established somatic benefits of active commuting, there is no evidence in this Finnish sample of a dose-response relationship between active commuting volume and anxiety or mental wellbeing. The study suggests that the mental health outcomes of active commuting may not follow a simple "more is better" or "more is worse" trajectory.

The paper posits that the discrepancy between somatic and mental health benefits may be due to the specific context of commuting (e.g., lack of autonomy, necessity vs. choice, and lower enjoyment compared to leisure-time activity). While greenness was correlated with higher active commuting, it did not enhance the mental health benefits of the activity in this dataset.

The authors conclude modestly that while active commuting supports planetary health through reduced emissions and improved cardiometabolic health, its role in promoting psychological wellbeing requires further investigation. They suggest that future research should focus on identifying specific modifications to active commuting environments or practices that could foster psychological benefits, thereby strengthening the integration of active commuting into the planetary health framework from a mental health perspective.