Actively Beneficial?

How should we describe a lifestyle change that doubles our likelihood of suffering a major traffic accident? Oddly,  evidence from Scotland suggests the answer is "worth making". Let me explain.

Active travel initiatives can be controversial, with some drivers wary of increased road congestion or other restrictions they fear might arise from dedicated active travel provision. On the other hand, active travel has been a great hope in public health policy, almost a proverbial holy grail. After all, truly attainable sources of prevention rather than cure in public health are few and far between. But to resolve this, we must face cold facts: infrastructure change is expensive, contested and difficult to deliver, often inspiring long-term skirmishes between interest groups. For this reason, potential and hope will never be enough by themselves - for such policies to become widespread, they have to be justified by hard evidence.

In July 2024 researchers from the universities of Glasgow and Edinburgh published longitudinal evidence from Scotland comparing health outcomes over the period 2001 to 2018 for three groups: non-active commuters, cycling commuters and pedestrian commuters. The two active travel categories, often bundled together in prior research, were compared long-term against the non-active control group, after controlling for pre-existing health conditions, and demographic and socioeconomic characteristics. To determine associations with a large variety of health outcomes, all subjects were linked to records of hospitalisation, death and medical prescriptions.

No study is perfect, and a notable restriction here lies in the available covariates from the Scottish Longitudinal Study, which did not include smoker status. It seems more than possible that smokers would cluster in the non-active and pedestrian active travel groups, due to the greater difficulty involved in cycling and smoking simultaneously. I say difficulty rather than impossibility because this writer has personally witnessed numerous smoking cyclists, but acknowledges that such sights are far from the norm! A further covariate-related weakness is that, even for the covariate set chosen, more than 25% of the initial sample had to be excluded for missing covariates. However, as with any analysis, the data is the data and the research must do the best it can. The final sample size of more than 82,000 participants remained substantial.

So, with those reservations in mind, what was found? It transpired that active travel of both types was significantly associated with reductions in a range of adverse physical and mental health outcomes. We will only cover some highlights here, but the open-access paper is worth reviewing. In summary, pedestrian commuters benefited from a 9% reduction in risk of any hospitalisation, 10% reduction in cardiovascular hospitalisation and 7% reduction in mental health prescriptions. Cyclists fared markedly better. Despite the previously flagged doubling of hospitalisation risk due to traffic collision, cycling was associated with a 47% reduction in risk for all-cause mortality, 51% lower risk of cancer mortality and 20% lower risk of mental health prescription over the period covered.

But what about that previously acknowledged concern that these results might be invalidated by cycling acting as a partial proxy for non-smoker status? This seems best addressed by considering earlier large scale research from University of Glasgow which used UK Biobank data with access to a smoking covariate. That study show a 41% reduction in all-cause mortality for two-wheeled commuters when smoker status was taken into account. In other words, while the mileage did vary a little, the direction of travel remains solidly towards strong benefit.

We can only imagine the difference such strong benefit might make at population level if we reduced the unacceptable risk from traffic collisions. Safety is a very real concern that stops many from getting on their bike in the first place. However, taking stock of the evidence in the round, it seems like the holy grail might not be a legend after all... Given that, I think I should head out for a cycle!