Throughout a person's life bone cells are broken down or reabsorbed by the body. But other specialized cells use calcium to build new bone.

As a person ages, the body reabsorbs the bone cells faster than it can replace them, which leads to a decrease in bone density.

Osteopenia vs. osteoporosis

Osteopenia is sometimes confused with osteoporosis. Although both conditions are related to bone density, they are not the same thing.

Osteopenia involves below normal levels of bone density. Osteoporosis is considered more serious than osteopenia because the extent of the bone loss is more severe.

Osteoporosis leaves bones fragile, which can lead to bone fractures even from minor falls. It can also lead to stooped posture, loss of height, and a collapsed vertebra.

Both osteoporosis and osteopenia are very common.

According to the National Osteoporosis Foundation, about 54 million people in the United States have osteoporosis. Many more people are estimated to have osteopenia.

It is important to understand that people with osteopenia are at an increased risk of developing osteoporosis.

Risk factors for developing osteopenia

Bone density peaks when people reach about 30 years old and gradually declines as they age.

People over the age of 50 have an increased risk of developing osteopenia. Women, especially those who are post-menopausal, are also at a much higher risk than men of developing the condition.

Estrogen plays a role in bone reabsorption and new bone growth. As estrogen levels decrease during menopause, the risk of osteopenia increases.

Men do develop osteopenia and osteoporosis, but much less frequently than women.

According to the Osteoporosis and Related Bone Diseases National Resource Center, about 2 million men are affected by osteoporosis.

One reason osteopenia occurs much more commonly in women is that their bones tend to be smaller and thinner than men's bones.

Asian and Caucasian women also have a higher risk of osteoporosis and osteopenia than other ethnicities.

Additional risk factors for osteopenia have been identified, including:

• Diet: A person who has a diet low in vitamin D and calcium may be more likely to develop osteopenia. Excessive alcohol use can also decrease the bone's ability to absorb calcium.
• Smoking: Calcium helps build strong bones. Smoking interferes with the amount of calcium the bones absorb and may speed up bone loss.
• Some medications: Certain medication can accelerate bone loss, especially in those people who take it for extended periods. For example, some anti-seizure medications, cancer drugs, and steroids may lead to a decrease in bone density.
• Certain medical conditions: Having certain medical conditions, such as lupus, rheumatoid arthritis, and celiac disease also increases a person's risk of developing osteopenia.