What condition is characterized by the loss of calcium from bones, leading to a weakened bone structure?

The condition characterized by the loss of calcium from bones, which results in a weakened bone structure, is osteoporosis. This disease often leads to an increased risk of fractures, as the bones become more fragile and less dense over time. Factors such as aging, hormonal changes (particularly in postmenopausal women), nutritional deficiencies, and sedentary lifestyle can contribute to the development of osteoporosis.

In contrast, arthritis involves inflammation of the joints, which can lead to pain and stiffness but does not primarily involve calcium loss from bones. Sarcoma refers to a type of cancer that originates in connective tissues such as bones, and while it can weaken bone structure, it's not specifically related to calcium loss. Osteomalacia involves the softening of bones due to vitamin D deficiency, affecting mineralization rather than a direct loss of calcium from existing bone tissue.