by Marcelle Pick, OB/GYN NP
There is no hard evidence that bone density correlates with bone strength or flexibility—the two factors that prevent fractures. In fact, bones can be dense (rich in calcium and hard), yet brittle—what matters more is the health of the collagen matrix, which keeps the mineralized bone supple and resilient.
The collagen matrix is a bedrock of nutrients and minerals that allows the bone to expand, contract, and mend without breaking. Think of the difference between a living, breathing sand dollar or sea urchin and its ossified shell. Or the difference between a slab of dried wood and a thinner piece that has been saturated in protective oils. While this is not an exact correlation, it may help you understand why a dense, hard covering can actually be more breakable than a thin but well-integrated whole—and why drugs like Fosamax and Actonel that focus only on bone density are not the answer.
In fact, BMD is not a reliable predictor of fractures. A study published in the 1995 New England Journal of Medicine reported that in 65-year-old women with no previous history of hip fracture, several other factors were more significant than bone density, such as tranquilizer and sleeping pill use, coordination, poor vision and depth perception; past history of hyperthyroidism, being tall, low blood pressure and rapid pulse, and lack of muscle strength.
In another study, published in JAMA in 1989, use of anti-anxiety medication like benzodiazapenes and other tranquilizers increased the risk of hip fracture by 70%. More recently, a large percentage of falls (and ensuing fractures) reported in a nursing home study were attributed to women rushing to the bathroom in the dark. For more on this and bladder control issues, please see our articles.
If this is the case, why has there been so much focus on density? One answer is that we actually have a test for it. Other factors influence bone health (and general health) are harder to quantify.