Ishii Shinya, Cauley Jane A, Greendale Gail A, Nielsen Carrie, Karvonen-Gutierrez Carrie, Ruppert Kristine, Karlamangla Arun S
Department of Geriatric Medicine, Graduate School of Medicine, University of Tokyo, Bunkyo-ku, Tokyo, Japan.
J Bone Miner Res. 2014 Dec;29(12):2561-70. doi: 10.1002/jbmr.2303.
Some aspects of an obese body habitus may protect against fracture risk (higher bone mineral density [BMD] and greater tissue padding), while others may augment that risk (greater impact forces during a fall). To examine these competing pathways, we analyzed data from a multisite, multiethnic cohort of 1924 women, premenopausal or early perimenopausal at baseline. Obesity was defined as baseline body mass index (BMI) > 30 kg/m(2) . Composite indices of femoral neck strength relative to fall impact forces were constructed from DXA-derived bone size, BMD and body size. Incident fractures were ascertained annually during a median follow-up of 9 years. In multivariable linear regression adjusted for covariates, higher BMI was associated with higher BMD but with lower composite strength indices, suggesting that although BMD increases with greater skeletal loading, the increase is not sufficient to compensate for the increase in fall impact forces. During the follow-up, 201 women had fractures. In Cox proportional hazard analyses, obesity was associated with increased fracture hazard adjusted for BMD, consistent with greater fall impact forces in obese individuals. Adjusted for composite indices of femoral neck strength relative to fall impact forces, obesity was associated with decreased fracture hazard, consistent with a protective effect of soft tissue padding. Further adjustment for hip circumference, a surrogate marker of soft tissue padding, attenuated the obesity-fracture association. Our findings support that there are at least three major mechanisms by which obesity influences fracture risk: increased BMD in response to greater skeletal loading, increased impact forces, and greater absorption of impact forces by soft tissue padding.
肥胖体型的某些方面可能会降低骨折风险（更高的骨矿物质密度[BMD]和更多的组织缓冲），而其他方面可能会增加这种风险（跌倒时更大的冲击力）。为了研究这些相互矛盾的途径，我们分析了来自一个多地点、多民族队列的1924名女性的数据，这些女性在基线时处于绝经前或围绝经期早期。肥胖被定义为基线体重指数（BMI）>30kg/m²。根据双能X线吸收法（DXA）得出的骨骼大小、BMD和身体大小构建了股骨颈强度相对于跌倒冲击力的综合指数。在中位随访9年期间，每年确定新发骨折情况。在对协变量进行调整的多变量线性回归分析中，较高的BMI与较高的BMD相关，但与较低的综合强度指数相关，这表明尽管BMD随着骨骼负荷增加而升高，但这种升高不足以补偿跌倒冲击力的增加。在随访期间，201名女性发生了骨折。在Cox比例风险分析中，肥胖与经BMD调整后的骨折风险增加相关，这与肥胖个体中更大的跌倒冲击力一致。经股骨颈强度相对于跌倒冲击力的综合指数调整后，肥胖与骨折风险降低相关，这与软组织缓冲的保护作用一致。进一步对臀围（软组织缓冲的替代标志物）进行调整后，肥胖与骨折的关联减弱。我们的研究结果支持，肥胖影响骨折风险至少有三种主要机制：对更大骨骼负荷的反应导致BMD增加、冲击力增加以及软组织缓冲对冲击力的更大吸收。
