Dr. Mirkin writes:

Hip Fracture Usually Requires Hip Replacement

The most-feared injury among serious bicyclists is a broken hip. The femur hip bone is shaped like a shepherd’s crook. The blood supply to the ball at the top of the hip bone comes in through the neck just below the ball. If the neck or ball are broken, the blood supply is usually shut off and the top of the hip bone dies.  To prevent this from happening, fractures of the ball or neck of the hip bone are usually treated with immediate hip replacement.  Try to avoid this drastic surgery by keeping your bones as strong as possible.

1) All exercise strengthens bones.  Bicycling strengthens bones, but not as much as sports that exert greater forces on bones such as running or lifting weights. (Medicine & Science in Sports & Exercise, March 2009).
2) Exercise increases calcium absorption, which is necessary for strong bones.

Read points 3 and 4 at www.drkirkin.com