Butting heads over bicycle helmets
==================================

* John C. LeBlanc

In her editorial,1 Mary Chipman states that the introduction of bicycle helmet legislation in Nova Scotia may have reduced cycling activity and the proportion of child cyclists2 (see Table 1 of her article). However, our study design precludes drawing this conclusion. We sought to maximize the number of cyclists observed in a fixed observation period. Due to availability of observers, we could not standardize observation times from year to year. Not surprisingly, we observed large variations in the number of cyclists per unit time, depending on the time of day, the day of the week, or the month. For example, during 1998 and 1999 we collected data almost exclusively during weekdays, which largely reflected adult commuter traffic. These variations in collection methods are a far more plausible explanation for the variation in cycling rates and proportion of child cyclists than the legislation. In support of this view, the owners of 3 major Halifax bicycle shops informed me that although bicycle helmet sales surged after the introduction of the legislation, there was no reduction in the sale of bicycles and no discernable impact on cycling activity.

Chipman refers to an Australian report by Dorothy Robinson3 that revealed cycling by children under 12 fell by 36% after the introduction of helmet legislation. However, Robinson did not discuss whether the decline persisted or whether those who stopped cycling substituted other equally beneficial activities. Chipman did not cite the study conducted by her colleagues who directly assessed the impact of helmet legislation on cycling behaviour in Toronto.4 They found that the rate of child cyclists before and after the introduction of bicycle helmet legislation actually increased from 4.3 cyclists per hour in the preceding year to 6.8 cyclists per hour in the year following the introduction of a law similar to the Nova Scotia legislation.

Wilhelm Kreyes raises important points about the influence of correct use of helmets on their effectiveness. Incorrect size, orientation or misuse of buckles undoubtedly reduce a helmet's ability to protect from injury. However, a proper assessment of these elements would necessitate a different study design.

Thomas DeMarco continues to be dumbfounded by the widespread support of the medical profession for helmet legislation. Without offering any evidence, he concludes that “ultimately, helmet laws save a few brains but destroy many hearts.” Such a conclusion cannot be drawn without knowing about the habits of those who abandoned cycling, and what activities if any they substituted in their quest for freedom from the burden of helmets. 

Finally, based on calculations not warranted by our study design, Malcolm Wardlaw comes to the remarkable conclusion that cycling activity in Halifax has been cut in half. In addition, he ignores published literature that shows cycling rates continue to increase after the introduction of legislation4 as well as accumulating evidence, summarized in a Cochrane review5 and a subsequent able defence against its critics,6 that has already shown that helmets are effective in preventing head injuries. This evidence cannot be dismissed by inappropriate secondary analysis of our data.

In summary, opponents of helmet legislation speculate that helmet legislation leads to increased cardiovascular deaths by discouraging exercise. First, is there clear evidence that the introduction of helmet legislation is followed by reduced cycling? Although our study cannot be used to address this question, the Australian study shows reduced cycling following legislation. However, the Canadian study indicates cycling continued to increase after the introduction of legislation. Second, do cyclists who oppose legislation and decide to stop become inactive and obese, or do they substitute other physical activity? No empirical evidence exists to respond to this question scientifically. Policy debate concerning the benefits and risks of helmet legislation must be rooted in evidence, not in speculation or strongly held views that ignore evidence to the contrary.

**John C. LeBlanc** Assistant Professor Dalhousie University Department of Pediatrics IWK–Grace Health Centre Halifax, NS

## References

1.  1. Chipman ML. Hats off (or not?) to helmet legislation [editorial]. CMAJ 2002;166(5):602.
    
    [FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiRlVMTCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiY21haiI7czo1OiJyZXNpZCI7czo5OiIxNjYvNS82MDIiO3M6NDoiYXRvbSI7czoyMDoiL2NtYWovMTY3LzQvMzM4LmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==) 

2.  2. LeBlanc JC, Beattie TL, Culligan C. Effect of legislation on the use of bicycle helmets. CMAJ 2002; 166(5):592-5.
    
    [Abstract/FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiY21haiI7czo1OiJyZXNpZCI7czo5OiIxNjYvNS81OTIiO3M6NDoiYXRvbSI7czoyMDoiL2NtYWovMTY3LzQvMzM4LmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==) 

3.  3. Robinson DL. Head injuries and bicycle helmet laws. Accid Anal Prev 1996;28(4):463-75.
    
    [CrossRef](http://www.cmaj.ca/lookup/external-ref?access_num=10.1016/0001-4575(96)00016-4&link_type=DOI) 
    
    [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=8870773&link_type=MED&atom=%2Fcmaj%2F167%2F4%2F338.atom) 
    
    [Web of Science](http://www.cmaj.ca/lookup/external-ref?access_num=A1996VE55200006&link_type=ISI) 

4.  4. Macpherson AK, Parkin PC, To TM. Mandatory helmet legislation and children's exposure to cycling. Inj Prev 2001;7(3):228-30.
    
    [Abstract/FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6MTA6ImluanVyeXByZXYiO3M6NToicmVzaWQiO3M6NzoiNy8zLzIyOCI7czo0OiJhdG9tIjtzOjIwOiIvY21hai8xNjcvNC8zMzguYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9) 

5.  5. Thompson DC, Rivara FP, Thompson R. Helmets for preventing head and facial injuries in bicyclists. *Cochrane Database Syst Rev* 2000;(2): CD001855.
    
    

6.  6. Keatinge R, Thompson DC, Thompson R, Rivara FP. Helmets for preventing head and facial injuries in bicyclists. Comments. *Cochrane Database Syst Rev* 2000;(2):CD001855.