The National Osteoporosis Foundation recommends at least 30 minutes of weight-bearing activity most days of the week to help you preserve and build bone density. Weight-bearing exercise, such as jumping, running, walking or even using an elliptical trainer, stresses your bone tissue and encourages regeneration. Bicycling does not qualify as weight-bearing exercise because you don't support your weight against gravity. Always consult your doctor before starting this or any other exercise regimen.

Increased Risk

A February 2009 issue of "Medicine and Science in Sports and Exercise" published a study from the University of Oklahoma found that competitive male cyclists had lower bone density than a control group, with some even having the precursor to osteoporosis — osteopenia — despite otherwise being in excellent physical condition. Weak bones put women and men at risk of osteoporosis and fractures later in life.

Keep Bones Strong

You don't have to abandon cycling to keep your bones strong. Simply augment your weekly rides with strength-training exercises and occasional cross-training activity such as running, playing basketball or dance. If you need low-impact exercise, opt for the stair-step machine or a brisk walk outdoors or on a treadmill. Consume at least the recommended daily intake of 1,000 milligrams of calcium, advises "Bicycling," from foods such as yogurt, milk and greens.