Universal prescription

In April 2017 the UK Government unveiled its Cycling and Walking Investment Strategy (CWIS), the first binding legislation ensuring government investment in cycling and walking provision in England. CWIS commits 1.2 billion GBP of spending by 2020/2021, coming from central and local government as well as from local enterprise partnerships. While clearly falling within transport planning, and despite being less directly revenue-friendly than the recent UK tax on sugar sweetened beverages, it is appropriate to view CWIS as a public health initiative. Indeed the foreword to the policy cites better health and improved air quality among the benefits sought by doubling cycling activity by 2025.

We'll consider this development through the lens of the mortality and morbidity impacts that could arise should this policy be successful. Why should a government be making such specific commitments to active travel? Encouraging people to make more journeys without a car isn't just about improving air quality, although, since World Health Organisation estimates suggest air pollution contributes to more than five percent of all deaths globally, that is one excellent reason.

In a wider context, high quality evidence for the impact of active travel on health has been accumulating to the point it can scarcely be ignored. A study into active commuting from the University of Glasgow covering more than 260,000 participants suggested a minimum 40% reduction in all-cause, cardiovascular, and cancer mortality between cycle commuters compared to non-active travellers. To paraphrase George Orwell's Animal Farm, this might be considered a case of "two-wheels good, four-wheels bad", although since statistically significant benefits on cardiovascular incidence were also observed for walking, and other recent research has found impressive longevity benefits arising from running, it appears the wheels are far from mandatory.

However, no area in science is completely without controversy. A recent twin-study from Finland sought to investigate causality between exercise and mortality outcomes. The study examined the impact where one twin exercised and the other did not. The human results for non-twin groups and non-identical twin groups supported the contention that exercise is protective, however, for monozygotic (MZ), or identical twins, it appeared to show no such effect. The team suggested that the genetic factors that increase propensity to high baseline physical activity, might also determine longevity. This hypothesis seems undercut by two facts, however. Firstly that the MZ twin population studied, despite sharing identical genes, by design did not share the same baseline physical activity levels. Furthermore, the human study dataset contained a mere thirty-four twin-pairs and a tiny number of deaths, which is too small to support any robust conclusion. There is clearly more science to be done here, but this result, by itself, appears insufficient to overturn a strong and growing consensus.

Another area of current societal concern is around mental health. Mental-illness, and the psycho-social impacts that may arise from it, can have alarming mortality consequences. One recent global review suggested a median impact on life expectancy of ten years, an impact comparable with that of lifelong heavy smoking. Here too, exercise has been consistently found to be of value, with protective effects found against both depression and anxiety disorders.

Finally, it has long been suggested that exercise may be protective for the aging brain, and recent research would seem to back this up. A meta-analysis across thirty-nine different studies found improved cognitive function went hand-in-hand with regular exercise. The review results were seen as providing clinicians with the evidence needed to prescribe exercise to their patients. Given the impressive evidence-base overall, a population-wide prescription for increased active travel seems, from a longevity perspective, to be just what the doctor ordered.