There is rarely a silver lining that does not come with a cloud, and often the cloud is bigger than the lining. A fine example is bicycle helmets. They provide such an obvious good that, at first glance, you’d think everyone would wear one, even without a law mandating it. Why would anyone risk their skull in a bicycle accident if injury were prevented by merely wearing a particular hat? Yet half the people ride without, even when there are laws and fines. There are some down-side to helmets, but they are so small that even mentioning them seems small. Helmets are inconvenient, and this causes people to ride a little less, so what?

Hospital admissions for bicycle-related, head injuries, red, left scale, and bicycle-related, non-head injuries, blue, right scale. The ratio is 1:2 before and after the helmet law suggesting that helmet law did nothing but reduce ridership.

As to turns out, helmets hardly stop accidental injury, yet cause people to ride a lot less, and this lack of exercise causes all sorts of problems — far more than the benefits. In virtually every city where it was studied, bicycle ridership dropped by 30-40% when helmets were required, and as often as not, those who still rode, rode unhelmeted. There was a 30-40% decrease in head-trauma injuries, but it appears that this was just the result of 30-40% less ridership. You’d expect a larger decrease if the helmet helped, as such.

Take the experience of Victoria, Australia; head and non-head bicycle injury data plotted above. Victoria required bicycle helmets in January 1990. Before then, in the peak summer months, hospital records show some 50 bicycle-related head injuries per month, and 100 bicycle-related, non-head injuries — a 1:2 proportion. Later, after the law went into effect, each summer month saw about 35 bicycle-related, head injuries, and 70 bicycle-related, non head injuries. This proportion, 1:2, remained the same suggesting the only effect of the helmet law was to reduce ridership, with no increase in safety. The same 30% decrease was seen by direct count of riders on major streets, though now a greater proportion of those still riding were flaunting the law, and not wearing helmets.

One reason that helmets don’t help much is that the skull is already a very good helmet. As things stand, the main injury in a bicycle flip does not come from your skull cracking, it comes from your brain hitting the inside of your skull, and a second helmet doesn’t help stop that. There’s no increase in safety, and perhaps a decrease as the helmet appears to decrease vision. In a study of bicycle-injury-related highway deaths, Piet de Jong found that countries with the highest helmet use had the highest highway death rates. The country with the highest helmet use (the USA, 38% helmeted) had the highest cyclist death rate, 44 deaths per 1,000,000,000 km. By comparison, the nation with the least helmet use (Holland, 1% helmeted) had among the lowest death rates, only 10.7 deaths per 1,000,000,000 km. There are many explanations for this finding, one sense is that the helmets hurt vision making all types of injury and death more likely.

From the national cancer institute. An hour or three of exercise per week adds years to your life — especially among the middle aged. Note these are healthy weight individuals. 

Worse than the effect on visibility, may be the effect on exercise. Exercise is tremendously beneficial, especially for middle-aged people in a sedentary population like the US. The lack of exercise is a lot more deadly, it turns out, than any likelihood of flying over the handlebars. How do I know? From studies like the National Cancer institute, shown at right. To calculate the cost/benefit of a little riding, less say you ride 3 hours per week at 10 mph (slow roll). The chart at right suggests a middle-aged person will add 3.4 years to your life, or about 10% life extension. Now consider the risks. This person will ride 30 miles per week, or 2400 km per year. Over 35 years the chance of death is only 0.36%. In order to get a 10% chance of death, you’d have to ride, over 2.3 million km, or 1000 years. Clearly the life extension benefit far outweighs the risk from fatal accident.

But life extension isn’t the total benefit of exercise. Exercise is shown to improve metal health, reducing depression and ADD in children, and likely in adults. Exercise also helps with weight loss, and that is another big health benefit (the chart above was for healthy body weight riders). So my first suggestion is get rid of bicycle helmet laws. I would not go so far as to ban helmets, but see clear disadvantages to the current laws.

The other suggestion: invent a better helmet. While most helmets are vented, and reasonably cool while you ride. They become uncomfortably hot when you stop. And they look funny in a store or restaurant. You can’t easily take them off, either: Restaurants no longer have hat racks, and stores never had them. What’s needed is a lighter, cooler helmet. Without that, and with helmet laws in place, people in the US tend to drive rather than ride a bicycle — and the lack of exercise is killing them.

Robert Buxbaum, January 19, 2017. One of my favorite writing subjects is the counter-intuitiveness of health science. See, eg. on radiation, or e-cigarettes, or sunshine, or health food. Here is a general overview of how to do science; I picked all the quotes from Sherlock Holmes.