Data from: Computed tomography shows high fracture prevalence among physically active forager-horticulturalists with high fertility

Modern humans have more fragile skeletons than other hominins, which may
result from physical inactivity. Here we test whether reproductive effort
also compromises bone strength, by measuring using computed tomography
thoracic vertebral bone mineral density (BMD) and fracture prevalence
among physically active Tsimane forager-horticulturalists. Earlier onset
of reproduction and shorter interbirth intervals are associated with
reduced BMD for women. Tsimane BMD is lower versus Americans, but only for
women, contrary to simple predictions relying on inactivity to explain
skeletal fragility. Minimal BMD differences exist between Tsimane and
American men, suggesting that systemic factors other than fertility (e.g.
diet) do not easily explain Tsimane women's lower BMD. Tsimane
fracture prevalence is also higher versus Americans. Lower BMD increases
Tsimane fracture risk, but only for women, suggesting a role of weak bone
in women's fracture etiology. Our results highlight the role of
sex-specific mechanisms underlying skeletal fragility that operate long
before menopause.

现代人类的骨骼相较于其他人亚科成员更为脆弱，这一现象或源于身体活动不足。本研究针对身体活动活跃的齐曼（Tsimane）觅食-农耕混合型族群，通过计算机断层扫描（computed tomography）测量其胸椎骨矿密度（bone mineral density, BMD）与骨折患病率，以此检验生殖负担是否同样会损害骨骼强度。
女性首次生育年龄越早、产次间隔越短，其骨矿密度越低。相较于美国人群，齐曼族群的骨矿密度更低，但该差异仅见于女性，与仅以身体活动不足解释骨骼脆弱性的简单预测相悖。齐曼与美国男性的骨矿密度差异极小，这表明除生育因素外的系统性因素（如饮食）难以解释齐曼女性更低的骨矿密度。
齐曼族群的骨折患病率也高于美国人群。较低的骨矿密度会升高齐曼族群的骨折风险，但该关联同样仅见于女性，提示骨骼强度不足在女性骨折病因学中发挥了作用。
本研究结果凸显了在绝经前很久就已发挥作用的、性别特异性骨骼脆弱性机制的重要性。