Achieving and maintaining a healthy skeleton is determined largely by a person's genetic endowment, operating under the influence of numerous factors, including proper diet, regular physical activity, adequate production of female and male reproductive hormones, estrogen and testosterone. If one or more of these factors is inadequate, deficits in the amount and quality of bone appear, leading to an increased risk for fractures, even in the absence of serious trauma. Such fractures are called fragility-fractures. Osteoporosis is a condition in which the amount of bone is reduced and there is disruption of its normal microscopic appearance. When deficiencies of diet, activity, or hormone concentrations occur as an adult, bone loss ensues.
Illness also constitutes a challenge to the skeleton.
This happens in several ways. Some illnesses directly affect the skeleton, particularly if they are associated with fever, inflammation, and weight loss, that is, with systemic manifestations. The effects of other illnesses may be less direct. Treatment of some conditions may make it necessary to restrict the diet or physical activity in ways that jeopardize the skeleton. Finally, some disorders may themselves cause no harm to the skeleton, but require long-term treatment with medications that have toxic effects on bone.