Bones are made up of cells, protein, and minerals. The presence of minerals, chiefly calcium and phosphorus, make the bone rigid. The more calcium and phosphorus you have in your bones, the larger and more dense they are. If these minerals are lost from bone, the bone becomes weaker and is more prone to fracture. When the loss of minerals is minor, it is called osteopenia and when it severe, it is called osteoporosis.
What causes mineral loss? From birth to death, bones are constantly undergoing a process of remodeling in which portions of the bone are broken down (called resorption) and then built back up again. Each bone in your body is completely turned over once every two to three months or so. Typically, before the age of 30 the rate of bone formation is higher than the rate of resorption so your bones increase in density. After bone mass peaks around the age of 30, the rate of resorption begins to exceed the rate of bone formation and so the bones lose mass.
The rate of bone loss is slowed considerably by the sex hormones testosterone and estrogen. In women, the onset of menopause that occurs around age 50 causes a rapid decline in the levels of estrogen in the body, greatly accelerating bone loss. Women can lose up to 20 percent of their bone mass in the five to seven years after menopause making them susceptible to osteoporosis. While testosterone levels also decline in men as they age, the decline is more prolonged. This difference largely accounts for why women are much more likely than men to experience bone loss and osteoporosis.
Besides the changes in hormone levels that probably cause most cases of osteoporosis, some other possible causes include:
- Being confined to a bed.
- Bone cancer.
- Cushing syndrome.
- Long-term use of corticosteroid drugs for conditions such as asthma, arthritis, skin diseases, and COPD.
- Thyroid problems.
- Inadequate intake of calcium or vitamin D (which helps you absorb calcium from your diet).
Researchers estimate that about 1 out of 5 American women over the age of 50 have osteoporosis. About half of all women over the age of 50 will suffer a fracture of the hip, wrist, or vertebra (bones of the spine).