In a strange twist, a health initiative many cities have adopted may be leading to a rise in bicycle-related head injuries. Bike-sharing programs are springing up around the country both to give people a convenient way to get around and to encourage exercise.

The problem is that the rental stations don’t include helmets with the bicycles they lend. So unless renters bring helmets with them, they go without. Seeing the risks this could pose, a group of American and Canadian researchers compared data from trauma centers in five cities from both before and after these bicycle programs were installed. They also looked at data from five cities that don’t offer bike-sharing as a control group.

Overall, the study found that in the cities with bike-sharing programs, there was a 14 percent greater risk of bicycle-related head injuries. With cities as large as D.C. and Miami participating, that statistic represents a disturbingly high number of people with damaged heads.

Is seems short-sighted if not dangerous to sacrifice one type of health for another. As admirable as the goal of promoting exercise among a city’s population is, if the programs are also encouraging a disregard for head safety, perhaps the model should be tweaked.

*Scientists have no conclusive evidence as to whether or how the reduction of g-forces during impacts reduces the number or degree of concussions and head injuries. GelDefender products provide supplemental padding as well as cooling and comfort benefits when used with helmets and caps. Participants in activities in which head impacts can occur should always use tested and approved helmets for protection. However, no helmet or supplemental padding can protect the user from all serious head or neck injuries that can result from impacts.