Background: Evidence exists to suggest that bicycle helmets may reduce the risk of head injuries to cyclists, however helmets are not uniformly worn by all bicycle users. Legislation has been enacted in some countries to mandate helmet use by cyclists, however the issue remains controversial with opponents arguing that this may inhibit people from bicycle riding and thus from gaining the associated health benefits, or that other countermeasures may have been responsible for decline in head injuries.
Objectives: To assess the effects of bicycle helmet legislation on bicycle-related head injuries and helmet use, and the occurrence of unintended adverse consequences.
Search strategy: We searched CENTRAL, the Cochrane Injuries Group's specialised register, MEDLINE, EMBASE, TRANSPORT and other specialist electronic databases, up to February 2006. In addition we searched government websites, handsearched selected journals and examined the reference lists of selected publications.
Selection criteria: We included studies that reported changes in either the number of head injuries, helmet use or bicycle use post- versus pre-legislation. Only studies that included a concurrent control group and which reported on the effect of legislation implemented at either the country, state or province wide level were included.
Data collection and analysis: Two authors independently extracted data and assessed methodological quality. The data were not appropriate for meta-analysis, thus the results of the included studies have been reviewed narratively.
Main results: Five studies, all from North America, met the inclusion criteria. For each of the studies, bicycle helmet legislation had been enacted for children only. Adults were used as controls in four of the studies, whilst jurisdictions with no helmet legislation were used as controls in the fifth. Three of the studies reported on changes in head injury rates and three reported on changes in helmet use. There were no included studies reporting change in bicycle use or other adverse consequences of legislation. In two studies, statistically significant decreases in head injuries were reported following the implementation of helmet legislation compared with controls, whilst one reported a non-statistically significant decline. Bicycle helmet use increased statistically significantly post-legislation in all three of the studies reporting on helmet use.
Authors' conclusions: Bicycle helmet legislation appears to be effective in increasing helmet use and decreasing head injury rates in the populations for which it is implemented. However, there are very few high quality evaluative studies that measure these outcomes, and none that reported data on an possible declines in bicycle use.