Bones Lack Normal Mineral Density

Q. Would you please explain the difference between “osteoporosis” and “osteopenia.” - M.A., Queens, N.Y.

A. Think of your bones like a kitchen sponge: When you’re young, the bones grow in length and become more dense. If you soak a kitchen sponge in plaster of Paris, the many holes contained within the sponge soak up the plaster to give it tremendous strength when the plaster dries. If you look at bone under a microscope, the framework is like the cellulose cells that make up a sponge: not too strong.

It’s the calcium mineral that gives bone its strength. Bone continues to gain density until we reach the age of 30. After that, bones begin to slowly lose their mineral density and strength. Men as a rule have heavier, denser bones than women. This is why osteoporosis affects fewer men than women.

As bone loses mineral density, there’s a point where the loss is great enough to say that the person has “osteoporosis”(think porous). The bone is weak, like a dry kitchen sponge. You can easily bend the sponge. But there’s a spectrum here between bone that is normal in mineral content and bone that has lost so much calcium that it’s weak and “osteoporotic.” Within that spectrum, there’s bone that has lost too much mineral density to be called normal; we call this bone condition “osteopenia” (“penia” means “lacking”, as in bone mineral content).

Osteoporosis is no trivial problem. More than 10 million Americans have osteoporosis; another 18 million have osteopenia, with osteoporosis looming in their future.

Risk factors include being female, fair-skinned, Asian (although African-American and Hispanic women are at risk too), having a thin or small frame, being elderly, having reached menopause, or having a complete hysterectomy, having a family history of osteoporosis, cigarette smoking, a diet low in calcium, chronic use of prednisone, a lifestyle lacking exercise, and excessive alcohol, and men with a low testosterone level.

The best way to determine if you have adequate bone mineral density is by having a painless and safe “bone density study”.

This is not the same test as a “bone scan,” which is a nuclear medicine study used to look for cancer, bone infection and stress fractures. The best bone density study is the DEXA scan, which checks your bone density in the hip and the spine.

It may not be available in some rural areas and a peripheral bone density study of the heel or wrist may be the only test available. It’s better than nothing but may give a “normal” test result when in fact there may be osteoporosis present in the hip or spine. The way that the test is interpreted is by comparing your bone density against two standards:

1) “Age-matched” standard, compares you against what’s expected for a person of your age, sex and size.

2) “Young-normal” standard, compares you against a healthy young adult of the same sex. The result comes as a “T-score,” with +1 and -1 as normal. A T-score of between -1 and -2 indicates there’s bone loss sufficient to say a person has osteopenia. A T-score of -2 or more means that there’s enough bone mineral loss for osteoporosis.

In terms of treatment, calcium (1,200-1,500mg/day), vitamin D and weight-bearing exercise will help reduce the amount of bone loss but won’t replace what you’ve lost. Estrogen hormonal replacement therapy will help reduce a woman’s chances of spine and hip fractures.

If osteoporosis is already present, drugs like Fosamax, Miacalcin, Evista and Calcitonin can help rebuild your weak bones and prevent compression fractures of the spine and broken bones elsewhere. For more information, visit the National Osteoporosis Foundation on the Internet at www.nof.org.