Is cycling bad for the bones? A number of intriguing studies published in the past 18 months, including Smathers’, have raised that possibility

Bone scans showed that almost all of the cyclists had significantly less bone density in the spine than the control group. Some of the racers, young men in their 20s, had osteopenia in their spines, a medical condition only one step below full-blown osteoporosis.

The riders, aged 27 to 44, began with slightly below-average bone density. By the conclusion of the race season, they had lost a significant portion of their total, already-low bone mass in their hips

Other endurance sports don’t seem to hurt bones in the same way and are typically beneficial.

many serious riders burn more calories in a day than they consume, an energy imbalance that is being studied to determine its impact on bone loss. And sweat could play a role. A rider can lose hundreds of milligrams of calcium an hour through sweat.