Flipping over lids

An extra from City cycling: health versus hazard

Should cyclists be made to wear helmets? It’s a question that sparks bitter debate within medical and public health communities. It's also a hot-button issue among cycling advocacy groups.

Bicycle helmets exist to protect their wearers from head injuries: anything from cuts and bruises to skull fractures. They can avert or reduce the severity of head traumas – but they are not perfect.

Today’s designs are largely ineffective at reducing rotational acceleration – the jiggling motion of the brain inside the skull that causes concussion – so designers have some catching up to do. One new approach is the angular impact mitigation system, which uses an elastically suspended honeycomb liner capable of absorbing some of the problematic rotational acceleration. It’s the subject of further study by a team of researchers from the USA, Austria and France.

New technology aside, few public health officials would argue with the idea that helmets offer protection in the event of a crash. The point of contention comes when people call for making helmet use mandatory. One fear is that forcing people to wear helmets creates the image of cycling as an unusually risky activity, one that requires special equipment that may be inconvenient to use. As such, it has the potential to deter people from cycling. The converse fear is risk compensation – the possibility that cyclists take more chances as a consequence of wearing a helmet.

“If you’re going to get a bang on the head, you’re better having a helmet on,” says Professor Ian Roberts from the London School of Hygiene and Tropical Medicine. He says that although bicycle helmets reduce injury in the event of a crash, whether they should be compulsory is a different question, and one that goes beyond science into the realm of values. As a regular cycle commuter and former paediatric trauma doctor who has seen more than his fair share of children seriously injured or killed in traffic accidents, Roberts wears a helmet, but doesn’t think that their use should be made compulsory.

Focusing on studies about helmet use in isolation, away from the other factors that contribute to the cycling environment, is also problematic. John Neary, Assistant Professor of Internal Medicine at McMaster University in Hamilton, Canada, and a local cycling advocate, explains: “The great majority of road traffic accidents are inflicted by motor vehicles, either on the users of other motor vehicles, or on non-users of motor vehicles,” he says. “Collision with a motor vehicle is so commonplace in our modern world that we think of it as a normal fact of life,” says Neary. “But it shouldn’t be.” And when research on helmets focuses on cycling behaviour, and ignores motorist behaviour, “that is victim blaming,” he says, “and should not be tolerated”.

What do the data say? Piet de Jong, a Professor in the Department of Applied Finance and Actuarial Studies at Macquarie University in Australia, crunched the numbers on the effects of helmets on cycling deaths and the health benefits of cycling for multiple countries, including the UK, the Netherlands and Denmark. His finding: helmets provide a small net benefit to health only in dangerous bicycling environments and, even then, under optimistic assumptions about the effectiveness of helmets and the likelihood of people’s wearing them. In places where cycling is safe, his analysis suggests that helmet laws have a substantially negative health impact.

The bike helmet debate represents a challenge for epidemiology, risk communication and evidence-based policy, say Dr Ben Goldacre, Wellcome Research Fellow in Epidemiology at the London School of Hygiene and Tropical Medicine, and Professor David Spiegelhalter from the University of Cambridge. In a recent commentary in the British Medical Journal, they note that cycling injury rates are low in Denmark and the Netherlands, even though many people cycle there and few cyclists wear helmets.

They say that low injury rates are achieved in these countries “through interventions such as good infrastructure; stronger legislation to protect cyclists; and a culture of cycling as a popular, routine, non-sporty, non-risky behaviour”. They add: “The current uncertainty about any benefit from helmet wearing or promotion is unlikely to be substantially reduced by further research.” Enmeshed in aspects of culture, psychology and politics, this contentious debate is unlikely to end any time soon.