A bone of contention

According to the American Osteoporosis Society, one in two women over 50 will break a bone because of osteoporosis. And although not exclusively a woman’s problem, 80 percent of the 10 million people diagnosed with osteoporosis in the US are women. Statistics in the UK are similar.

In the main, these grim figures are arrived at by testing women after menopause, when they are urged to have a DEXA scan (dual-energy X-ray absorptiometry). The results of this test largely determine whether women are given treatment for osteopenia (lowered bone mineral density) or full-fledged osteoporosis, which usually amounts to a lifetime of potentially dangerous drugs.

But the problem with determining treatment based on bone mineral density is that the DEXA scan itself is a blunt and inaccurate instrument. 

It works by sending an X-ray beam to the lumbar vertebrae and hips, which simply measures the shadows cast by the bones. From there, software in the machine then calculates the amount of calcium (in grams per square centimeter) in a given person’s bones, based on the density of the shadow.

And because this is a two-dimensional image, rather than three-dimensional, as in the case of a CT scan, this kind of rough estimate is open to all sorts of error. 

Dr Douwe Rienstra, an iconoclastic integrative physician who practices in Port Townsend, Washington, has written extensively about the problems with the DEXA scan. 

The first issue, he says, is that bone density can be vastly different in the same areas of the body. Studies have found that bone density can vary, for instance, by as much as 6 percent in the spine and 7 percent in the hip. 

Test results can also vary greatly depending on body size. Smaller people routinely register as having osteopenia or osteoporosis, simply because they have smaller bones, which cast a lighter shadow. Because the DEXA scanner has to travel further to get through a heavier person’s bones, it concludes that they have more calcium in their bones and thus heavier bone mineral density, even if the smaller person has an identical percentage of calcium in their bones. 

A study of 1,625 post-menopausal women confirmed that lower measures of bone mineral density were seen more often in smaller women.

The other issue is the reference points against which everyone is judged. Besides a Z-score (how you compare to others of the same age), those getting a DEXA scan receive a T-score, which compares their score to the bone mineral density of a strapping 20-year-old. 

And then there is the issue of different models of DEXA machines, which produce results that can differ by as much as 20 percent, according to Danish research. 

With newer DEXA scanners,  “normal” bone mineral density is calibrated by having researchers take the skeletons of cadavers, measure the bone volume and then use high heat to burn off everything but the mineral ash residue.  Measuring the ash, they believe, will provide the mineral content of the bone. 

According to Dr Rienstra, research shows that this method has “underestimated spinal density by up to 33 percent.”

Dr S. P. Nielsen,  a researcher at Hillerød Hospital, Denmark, summed up the entire problem of using bone mineral density to diagnose the state of our bones: “Bone mineral density is not an ideal measure of true bone density; it is not an ideal measure of bone strength; it does not predict fractures well;
and it has inherent problems of accuracy
and linearity.”

The greatest evidence of this was a large-scale Canadian study of more than 16,000 women over 50 diagnosed as having osteopenia, which compared their T-scores with their likelihood of sustaining a fracture.

Of the 765 fractures recorded in the study, most of the women with osteoporotic fractures were given T-scores that registered them as having normal bone mineral density values.In other words, the DEXA test was basically useless in predicting which women would go on to get fractures.

The study emphasized the need to look at clinical risk factors rather than bone mineral density when diagnosing osteoporosis. And the first place to look, as our Special Report this month advises (page 26), is your gut. 

New evidence shows that the strength of your bones has far less to do with the amount of calcium you consume and far more to do with the state of inflammatory factors in your digestive system, says Cate Montana. We also offer information about better and more accurate tests to use and the best vitamin and special herbal supplements to take.

Definitely worth boning up on. . . 

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