Animation of a close-up of healthy bone tissue, which then starts to break down due to osteoporosis. Healthy bone has a dense sponge-like structure which provides strength while keeping the bone light. Osteoporosis is shown beginning with a red flash, and then the bone starts to break down, losing much of its mass and weakening the bone. Osteoporosis results from an imbalance between bone formation and resorption, with too much resorbed. It is often due to hormone imbalances, notably in post-menopausal women, where low oestrogen levels lead to excess resorption. Affected bones become weak and prone to fracture.