Osteopenia and osteoporosis are diseases in which the bone’s mineral density is low, which increases the risk for fractures because the bones are thin. Osteoporosis is usually caused one by three things: excess parathyroid hormone, advanced age, and lack of estrogen in older females. If a patient fits into more than one of these categories, the risk is compounded. Osteopenia is similar, but simply refers to a lower bone mineral density (BMD) that is lower than normal but not quite low enough to classify as osteoporosis.