Bone Loss—Osteoporosis

Very similar to muscle loss, bone loss is the end result of various causes. Sickness behavior is once again at the center, as it causes immobility and loss of appetite. Since it was positively selected for short-term inflammatory reactions, it is also used again in chronic inflammations. This is accompanied by the loss of growth hormone, androgens, and the activation of stress axes, all of which promote bone degradation. In chronic inflammation, the activation of the immune system plays the largest role; in old age, the other conditioning factors are more significant. This also includes reduced sun exposure and thus a lower level of active vitamin D. Physical activity is the decisive factor in old age, as voluntarily increased activity leads to increased food intake and enhanced muscle and bone build-up, which often is missing during the process of aging.