Osteoporosis is caused by calcium deficiency. Due to the loss of calcium inside the bones, calcium deficiency leads to bone thinning, decreased bone mass, increased brittleness, and susceptibility to osteoporotic fractures. As age increases, the osteogenic effect of bone osteoblasts decreases and the osteoclastic effect of osteoclasts increases, which can lead to bone calcium loss and cause bone calcium deficiency. In women, after menopause, estrogen level decreases, which also leads to bone calcium loss and thus bone calcium deficiency causing osteoporosis. In addition, secondary factors are often due to medications, such as long-term, heavy use of glucocorticoids, such as prednisone and dexamethasone, or long-term bed rest resulting in reduced activity. Reduced absorption of calcium due to gastrointestinal disorders, such as frequent diarrhea, can also cause calcium deficiency in the bones, leading to osteoporosis.