Both osteoporosis and osteopenia are medical terms for progressive loss of bone density and thinning of bone tissue. Osteoporosis is a metabolic bone disease characterized by a severe decrease in bone mass that increases the risk of a fracture. Osteopenia refers to milder bone loss that doesn't yet meet the criteria of osteoporosis.

A simple, painless bone density test (densitometry) can detect the presence and degree of bone loss. Bone loss has many causes. The leading cause in women is a deficiency of the female hormone estrogen after menopause. The leading causes in men are decreased testosterone production and use of corticosteroid medications.

People with osteopenia can slow the progression to osteoporosis by doing weight-bearing exercise, such as walking, and consuming an adequate amount of calcium.

If you're a woman, the National Osteoporosis Foundation recommends that you have a bone density test if you aren't taking estrogen and any of the following conditions apply to you:

• You use medications that can cause osteoporosis, including corticosteroids such as prednisone, cortisone and dexamethasone.
• You have type 1 diabetes (formerly called juvenile or insulin-dependent diabetes), liver disease, kidney disease or a family history of osteoporosis.
• You experienced early menopause.
• You are postmenopausal, are older than age 50 and have at least one risk factor for osteoporosis, such as a family history of the disease, tobacco use or depression.
• You are postmenopausal, are older than age 65 and have never had a bone density test.

Doctors usually don't advise routine bone density testing for men because the disease is far less common in men.