A recent Gaceta Sanitaria letter concluded bicycle helmet use should not be mandated in urban areas.1 Mandatory helmet legislation (MHL) is controversial and a balanced presentation of all scientific evidence is therefore critical. This letter will briefly discuss relevant literature uncited by the authors.
The authors note bicycle use declines with MHL. However, there is ample evidence the contrary is possible. South Australian household surveys found similar cycling rates prior to and after MHL regardless of gender, age or level of urbanisation.2 Adelaide cycling counts increased by 2.9% after MHL. Other surveys from Victoria, Australia3 and Ontario, Canada4 indicate either no change or an increase in cycling following MHL.
New South Wales surveys were commissioned around the 1991 MHL to estimate changes in helmet wearing.5 These reports were designed to estimate helmet wearing and not cycling rates. No such surveys exist for NSW and conclusions using this data are therefore weak. However, this data forms the basis for the argument MHL leads to less cycling. Importantly, this data does not produce unequivocal results as Sydney adult cycling counts increased 22% following MHL.
Regarding the effects of MHL on urban cycling, the cycling mode share in Australian cities changed little after MHL from 1.14% in 1986 to 1.13% in 1991 after most Australians were subjected to MHL.
The above examples of non-decreasing cycling rates following MHL have important health implications. The de Jong paper, cited by Rojas-Rueda et al., assumes cycling rates only decline with MHL. However, as evidenced above, this does not hold uniformly. Importantly, for non-decreasing cycling rates, this model always estimates a benefit to MHL.
A New Zealand evaluation by Clarke and cited by Rojas-Rueda et al. ignores critical analyses found in the original source material.6 This research demonstrates serious traumatic brain injury rates per million hours spent cycling declined significantly following MHL. Clarke only considered all cycling injuries and, since helmets are designed to protect the head only, his analysis could mask any positive impact of MHL.
The manuscript mentions Australian research demonstrating a benefit of MHL, yet cites a rejoinder critical of this work. Missing from the letter was a full-length response to the rejoinder demonstrating the criticisms were unfounded and the original analysis was rigorous and robust.7 Briefly, the original study estimated a 29% decline in bicycle related head injury hospitalisations attributable to MHL compared with limb injuries. There was a concurrent helmet wearing increase from about 25% to 80%. Note the rejoinder self-cites a paper retracted due to numerous arithmetic errors.8
There is strong evidence helmet wearing, either voluntarily or compulsory, mitigates the risk of bicycle related head injury. Of note, head injury is the most common cause of cycling-related hospitalisation in Catalonia.9 Helmets, however, should not be viewed as a panacea and instead are an important part of any cycling safety strategy along with segregated cycling facilities and lower speed limits for motorised traffic. The benefits of each intervention are situational -- helmets will help a cyclist in an accident and segregated cycling infrastructure will help avoid accidents. I therefore believe the decision to mandate helmet use should be in conjunction with a comprehensive strategy and not in isolation.
