A study last year by the Institute of BioSciences in Brazil found that adolescents who practiced Judo had a significant increase in bone mineral density. This increase resulted in benefits to bone health associated with protection against osteoporosis and fractures that typically come with age and inactivity later in life.
The study found that "high-magnitude forces through muscle pulling on the bone, ground reaction forces intensified by the absence of footwear to attenuate impact shocks and high-impact loading of the skeleton due to repeated falls on the ground" has a significant positive influence on bone mass development.
In short: Judo throws and falls are one of the best ways to ensure bones develop strong and healthy.
See the full study here: http://www.sciencedirect.com/science/article/pii/S2359348215000913