DXA Scan Shortcomings

A DXA scan is a good tool for measuring bone density but it doesn’t measure bone quality.

 The DXA scan is used to identify people at risk for broken bones and osteoporosis, but the DXA scan only measures one part of bone health – bone density. That’s because a DXA scan hones in on calcium content. Calcium in bone is an inorganic mineral and thus quite weighty. A DXA scan sees weight as a sign of improved bone density, but it’s more complicated than that.

We all know calcium is essential for bone health, but it’s just one factor. Moreover, too much calcium is actually bad for bones – it makes bone brittle and increases the risk of fracture. Think of a piece of chalk (which is almost all calcium) and how easily it breaks. Bones are the same and consuming too much calcium without other balancing vitamins and minerals is not healthy. More that 2,000 mg of calcium a day makes bones brittle, and also poses a heightened risk of heart attack.

The calcium content of bone doesn’t show true bone strength. There are plenty of fragility fractures in women with normal DXA scans because the DXA scan doesn’t measure the organic part of bone - the collagen, proteins, and cells. The organic part of bone is what gives bone its resilience and toughness and protects against fracture after a fall or injury.

Most of the research about calcium and vitamin D supplements is measured by changes in DXA scans. But the true measure of nutrition is whether the number of fractures decreases, not whether the DXA scan improves.

The best bone health supplements provide nutrients that help balance and enhance calcium as well as the organic part of bone. Not only does the addition of other, well-researched vitamins and minerals help drive calcium into bone, it keeps calcium away from other parts of the body like the heart where it can do harm.

Studies of supplementation with vitamin K have shown decreased fracture rates even when the DXA score stays the same. Vitamin K activates a special protein in bone called osteocalcin that glues calcium to collagen. A stronger bond means stronger bone. Vitamin D also stimulates the production of osteocalcin, but vitamin K adds an extra unit to the osteocalcin that really makes it like superglue. Without adequate vitamin K, the glue that binds calcium to collagen may be weak.

Another thing your DXA scan doesn’t provide is the health of the bone collagen itself. Collagen consists of strands of protein that are woven together. There are cross-links between the strands of collagen that help make the collagen stronger. Fewer cross-links make collagen weaker and more brittle. Bone biopsies of women with fragility fractures, yet ‘normal’ DXA scans, have shown poor cross-linking of the collagen in bone.

Boron and silicon are essential nutrients that increase the amount and strength of collagen. These essential nutrients also increase the cross-linking of collagen. Studies in humans have shown that supplementation with silicon can improve the amount and strength of collagen. Silicon supplementation has also helped strengthen hair and nails because hair and nails have the same type of collagen as bone.

The DXA scan also fails to measure the structure and shape of bone. Inside the bone there are many struts called trabeculae that provide extra strength. These struts can lose calcium evenly, or in spots. Bones in different people may have the same amount of calcium, but it’s evenly distributed in one person and uneven in another. The uneven calcium distribution may lead to holes or weak areas that are more likely to break.

In men with lower bone density, these struts are more likely to thin out evenly - while in women the struts are more likely to thin unevenly and the middle of the struts may disappear completely. This results in more total bone weakness because the struts themselves are broken instead of evenly thinned. The DXA scan may show equal calcium content but the distribution of that calcium is difficult to measure.

Larger bones are also stronger than smaller bones even when they have less calcium. This is another reason why men and larger women are less likely to break a bone than smaller women. Broken bones definitely do occur in men and larger women, but their bone density isn’t telling the whole story of why their bones were fragile.

The real measure of bone health is strength and resistance to breaking, and this depends of total bone quality.

If your DXA scan appears normal but you have broken a bone by falling or tripping from a standing height (which is called a fragility fracture) - your bones are not in good shape. In fact, anyone over the age of 50 years who has a broken hip or vertebra from a fall without major trauma is automatically diagnosed with osteoporosis regardless of their DXA score.

Women who have never had a broken bone may actually have fairly strong bone despite a low DXA score and should be careful before jumping into taking osteoporosis drugs. There’s a good chance proper supplementation may be enough. This is another reason to make sure you choose a high quality bone health supplement to provide essential bone nutrients in addition to calcium and vitamin D.

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