How did active travel relate to later BMI and mental health?

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Active travel, such as walking and cycling, is increasingly recognized as a potential way to increase physical activity and contribute to physical and mental health. Much of the evidence on its health benefits, however, comes from cross-sectional data, leaving it uncertain whether active travel improves health or healthier people are more inclined to travel actively.

The study systematically examined relationships in both directions between active travel and two health outcomes: body-mass index (BMI) and mental health. Researchers estimated random-intercept cross-lagged panel models using 10 waves (years) of data from the Longitudinal Internet Studies for the Social sciences panel, which is representative of the Dutch population. Active travel was assessed using walking frequency, and mental health was measured with the 5-item mental health inventory (MHI-5).

The results indicated that active travel did not affect later BMI, whereas BMI negatively influenced later active travel. This pattern was consistent with earlier research on general physical activity and BMI. For mental health, the pattern was the opposite: the effect of active travel on later mental health was significant, while the reverse effect was not, at the 5% significance level.

The findings underline that cross-sectional estimates of effects between active travel and health outcomes should be interpreted with care, because effects can occur in either direction. They also suggest that lowering BMI in the population, for example through dietary programs, may increase the uptake of active travel.