Osteoporosis is the thinning of bone tissue and loss of bone density over time.

Osteoporosis is the most common type of bone disease.

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 have a fracture of the hip, wrist, or vertebra (bones of the spine).

Osteoporosis occurs when the body fails to form enough new bone, when too much old bone is reabsorbed by the body, or both.

Calcium and phosphate are two minerals that are essential for normal bone formation. Throughout youth, your body uses these minerals to produce bones. If you do not get enough calcium, or if your body does not absorb enough calcium from the diet, bone production and bone tissues may suffer.

As you age, calcium and phosphate may be reabsorbed back into the body from the bones, which makes the bone tissue weaker. This can result in brittle, fragile bones that are more prone to fractures, even without injury.

Usually, the loss occurs gradually over years. Many times, a person will have a fracture before becoming aware that the disease is present. By the time a fracture occurs, the disease is in its advanced stages and damage is severe.

The leading causes of osteoporosis are a drop in estrogen in women at the time of menopause and a drop in testosterone in men. Women over age 50 and men over age 70 have a higher risk for osteoporosis.

Other causes include:

• Being confined to a bed
• Chronic rheumatoid arthritis, chronic kidney disease, eating disorders
• Taking corticosteroid medications (prednisone, methylprednisolone) every day for more than 3 months, or taking some antiseizure drugs
• Hyperparathyroidism

White women, especially those with a family history of osteoporosis, have a greater than average risk of developing osteoporosis. Other risk factors include:

• Absence of menstrual periods (amenorrhea) for long periods of time
• Drinking a large amount of alcohol
• Family history of osteoporosis
• History of hormone treatment for prostate cancer or breast cancer
• Low body weight
• Smoking
• Too little calcium in the diet