Cycling is a non-weight bearing activity and this, combined with the biomechanics of cycling, is thought to be insufficient to stimulate bone formation.
Several observational studies indicate that cyclists can have low (or reduced) bone density in the lumbar spine and femoral neck . Moreover, another study showed that two-thirds of professional cyclists have low bone mineral density .
Cyclists can lower their risk of bone density issues by combining cycling with weight-bearing activities such as resistance training, and consuming adequate calcium (1200-1500 mg/day) and vitamin D (800+ IU/day) .
Find more information on nutrition for cyclists in our ultimate guide here.
 Beatty, T., Webner, D., & Collina, S. J. (2010). Bone Density in Competitive Cyclists. Current Sports Medicine Reports, 9(6), 352–355. https://doi.org/10.1249/jsr.0b013e3181ffe794
 Olmedillas, H., González-Agüero, A., Moreno, L. A., Casajus, J. A., & Vicente-Rodríguez, G. (2012). Cycling and bone health: a systematic review. BMC Medicine, 10(1). https://doi.org/10.1186/1741-7015-10-168