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Bone loss is a known and well studied hazard of microgravityexd.
Low gravity is one of the unanswered questions, 0g has been studied with humans, mice, and other animals. Higher than 1g has been studied with chickens but there have so far been no low-g studies.
These effects can be mitigated on the Moon by exposing the settlers continuously to a centrifuge and with a strong exercise program.