Intended for healthcare professionals

Letters Commuting and incident disease

Benefits of active commuting—causality matters

BMJ 2017; 357 doi: https://doi.org/10.1136/bmj.j2425 (Published 19 May 2017) Cite this as: BMJ 2017;357:j2425
  1. David Colquhoun, research professor
  1. University College London, London, UK
  1. d.colquhoun{at}ucl.ac.uk

Although the paper by Celis-Morales and colleagues on active commuting has the usual token nod to the problem of causality, it is written as though it shows that cycling to work has numerous benefits.1 The related editorial is even more cavalier—its title, “Active commuting is beneficial for health,” is a direct statement of causality.2

Celis-Morales and colleagues do not mention the possibility of reverse causality. People with heart disease or cancer might be incapable of walking or cycling to work, or at least be disinclined to do so. People who cycle to work are also very likely to be health conscious in other ways.

Of course I am 100% in favour of people walking or cycling to work. It would make the streets a lot more pleasant for everyone. But evangelism should not replace science. Causality really matters.

Footnotes

  • Competing interests: None declared.

References