Really? Anahad O’Connor tackles health myths.

THE FACTS

Last week, New York City began its long-awaited bicycle sharing program, the largest in the nation. As in many other cities, helmet use was made optional, in part to encourage greater participation.

But a look at the statistics suggests that riding without a helmet is not a decision to make lightly. While football tends to dominate the discussion of sports-related head injuries, research shows that bike accidents account for far more traumatic brain injuries each year.

According to the American Association of Neurological Surgeons, cycling accidents played a role in about 86,000 of the 447,000 sports-related head injuries treated in emergency rooms in 2009. Football accounted for 47,000 of those head injuries, and baseball played a role in 38,394.

Cycling was also the leading cause of sports-related head injuries in children under 14, causing 40,272 injuries, roughly double the number related to football (21,878).

Part of the reason is that bicycling is so ubiquitous. But people are also more cavalier about taking precautions, said Dr. Gonzalo Vazquez-Casals, a neuropsychologist at Jamaica Hospital Medical Center in New York.

Bicyclists are also at high risk of colliding with motor vehicles, and when riders are not wearing helmets, such collisions frequently result in serious head injuries. For example, about 90 percent of bicyclists killed in the United States in 2009 were not wearing helmets. A majority were middle-aged men.

In New York City, 75 percent of all fatal bike accidents involve a head injury. In addition to wearing a helmet, another helpful precaution is using a marked bike lane: Streets that have them have 40 percent fewer crashes ending in death or serious injury.

THE BOTTOM LINE

Bike accidents contribute to more sports-related head injuries than any other activity.