What is Osteopenia? And How Can Yoga Help?

by Shari

Last Friday Baxter answered a reader’s question about osteopenia (see Friday Q&A: Yoga and Osteopenia), regarding whether or not yoga practice on its own is sufficient to maintain and/or increase bone strength. By chance, we recently received a request for an article addressing “dangerous” poses for osteopenia. Since most of you probably don’t know much about osteopenia—and its relationship to osteoporosis— we decided it was about time to provide some background information about the condition. I promise I’ll get around to answering the reader’s question eventually! Look for it this coming Friday.

Let’s start by discussing osteoporosis, which is a disease in which bones become fragile and are more likely to break or fracture due to loss of density (not bone strength). It is not painful and many people (both men and women) don’t even know they have it or are at risk for developing it until they take a DEXA scan. The DEXA scan (dual energy X-ray absorptiometry scan) measures bone mineral mass, because medical researchers have discovered that there is a correlation between bone breaking and bone density loss. But the DEXA scan can also cause lot of confusion because it doesn’t take into consideration the different way bones are constructed. Some bones are short and fat, and some are long and thin, and differently shaped bones can have different density readings. Bone mass is affected by both how densely a bone is constructed and by its corresponding physical dimensions.

Femur Bone

The World Health Organization has defined the statistical measurements of bone density through a system of comparing your numbers to women of the same age, height and weight, and then comparing them to the average measurements of women age 25-30 that are at the peak of bone strength. Three areas are measured in the DEXA scan: lumbar spine, total hip, and surgical neck of the femur (thigh bone). Two scores are given:

• T score, which is the measurement of bone mineral density and how your score compares to healthy 25-30 year old women.
• Z score, which is the comparison to women your age, height and weight.

Osteopenia is defined as a T score of 1 to 2.5 standard deviations below the mean (negative numbers), and means that you are at risk for developing osteoporosis. Osteoporosis is defined as a T score of 2.5 standard deviations below the mean (negative numbers). The higher the T score (or the more negative the numbers), the higher the fracture risk.

The correlation between a low bone mineral-density reading in a DEXA scan and a higher fracture risk is stronger than the relationship between high blood pressure and a stroke. But even though the test detects 9 out of 10 people with osteoporosis, the test is not perfect and it wrongly diagnoses healthy bones between 5-7% of the time. Also, readings will differ in different test sites, so for consistency the same test facility needs to be used for repeated scans.

So how does yoga fit into this picture? Bone has two main components: outer bone and inner bone. Bone is a living matrix of living cells and canals that are interrelated. Outer bone, which surrounds inner bone, is called the cortex and it forms a hard outer ring and is a large part of bone strength. Its construction is fairly uniform in individuals. Inner bone is spongy and is called cancellus or trabecular bone. It varies greatly in individuals. For us to improve our bone health we want to not only build outer bone but also inner bone.

Wolff’s law describes bone strength as follows:

1. The architectural strength of a bone develops along the lines of force that the bone is subjected to.
2. If a bone is loaded, the bone will remodel itself over time to become stronger and resist that sort of loading.

In conjunction with Wolff’s law there are some other important forces that act on the bones to improve bone strength and density:

1. Gravity increases bone loading. 
2. Muscle contraction increases bone loading. Dynamic tension occurring between muscle agonist and antagonist affects the bones by applying opposite pressures, and the forces are doubled on the bone.
3. Muscle activity stimulates bones to strengthen themselves more vigorously than weight bearing alone.

In our yoga asana practice, we not only take weight-bearing positions, such as standing poses, but all the active poses involve muscle contraction in some form. And the great variety of poses and movements means that all your bones are involved! In addition, Dr. Loren Fishman cites from his extensive research on osteoporosis that bone stimulation (growth) occurs after 12 seconds of static (isometric) hold but not more after 72 seconds of hold. 20-30 second holds are recommended for bone stimulation. And 20-30 second holds are quite typical for many of the poses we practice.

Now you can see why yoga is recommended for people with osteopenia as a way to prevent the development of osteoporosis and is also considered beneficial for people who already have osteoporosis. And for those of us who don’t have either condition, yoga is a very versatile and adaptable way for maintaining our bone strength. However, because osteopenia means more fragile bones, certain yoga poses are considered risky for people with the condition. Tune in Friday for my answer to the reader’s question about those poses.