Men's Osteoporosis Support GroupFactors affecting bone mineral density Clin Exp Obstet Gynecol. 2009;36(2):87-90. Factors affecting bone mineral density of young women and predictive factors of low bone mineral density. Ikeuchi K, Umesaki N. PMID: 19688949. This Japanese study looked at the factors that influence bone mineral density (BMD) in young women aged 19 to 24. Using dual-energy X-ray absorptiometry (DXA), they found body weight (BW), serum N-terminal telopeptide of type 1 collagen (NTx), and bone specific alkaline phosphatase (BAP), which are bone turnover markers, significantly correlated to BMD. The authors concluded, "In young women, BW and bone turnover markers significantly affected BMD. Low BMD can be indicated using BW and NTx concentrations without measurement by DXA." Editor's comments. The authors are suggesting that rather than using DXA, which is time consuming and expensive, merely weighing someone and doing serum NTx would indicate who has decreased BMD. Osteoporosis is literally defined as a state of having decreased BMD, that is, a T-score less than -2.5. The abstract doesn't state the exact T-score that any of the young women had, which would have been helpful. Are they implying that these 19-24 year old women are at risk for fractures because of the reduced BMD that is related to their weight and NTx? I'm aware of no research showing prevalent fractures in young premenopausal women (or young men) that have low body weight and low BMD. This is a complex issue that I freely admit I don't fully understand. But it seems to me that bone is a functional tissue that responds to factors such as stress, weight, exercise, and others that are placed on it. It seems logical that people of lower body weight would have lower BMD. Does that mean their bone is weaker than a heavy individual with greater BMD? Yes, certainly if that bone is abnormal and weakened. But if it is normal bone, but of a smaller size, thus with less density, why wouldn't it support an individual weighing less? I can picture a roof with smaller beams that can adequately support lighter shingles or roofing materials. These small beams are not as dense as heavier beams would be. But why use heavier, denser beams if the roofing material is lightweight and never needs to support heavy snow or other materials? This seems a particularly important instance where we'd need more than bone density as a measure of strength. The materials and methods of the following study might eventually be useful to resolve the questions I have: J Bone Miner Res. 2008 Sep;23(9):1426-34. In vivo microMRI-based finite element and morphological analyses of tibial trabecular bone in eugonadal and hypogonadal men before and after testosterone treatment. Zhang XH. PMID: 18410234. Note this study is available in full free text also. It, however, is not light reading, so be forewarned. The authors used microMRI and microfinite element modeling to evaluate the strength and physical properties of bone, not just its BMD. I have no idea whether these micro techniques will ever be applicable on a large-scale basis, how expensive and/or time consuming they are, etc.. I'll watch for future research on this topic and report its results.
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