Vitamin D deficiency is a global health problem in all age groups, especially in the elderly population. Serum 25(OH)D is the biomarker to assess vitamin D nutrition status. However, the free hormone hypothesis proposes that free vitamin D might be a more reliable marker of vitamin D nutrition status. Thus, the aims of this study were to (1) evaluate the distribution of free 25OHD in elderly individuals, and (2) to assess the association between free 25OHD and total 25(OH)D, 1,25(OH)2D, 24,25(OH)2D, calcium (Ca), alkaline phosphatase (ALP), and phosphorus (P) in elderly population. A total of 312 healthy elderly individuals were enrolled in this study and residual serum samples were collected. Free 25OHD, total 25(OH)D, 24,25(OH)2D, and 1,25(OH)2D were measured using LC-MS/MS. Other biochemical analytes were measured using automatic analyzers. Our results showed that with an increase in the levels of total 25(OH)D, the levels of 25(OH)D3, 1,25(OH)2D, 24,25(OH)D, and free 25OHD increased, whereas the levels of 25(OH)D/24,25(OH)2D decreased. Further, we observed that the level of free 25OHD was significantly positively correlated with the total 25(OH)D (r = 0.226, P < 0.001), 25(OH)D (r = 0.221, P < 0.001), and 24,25(OH)2D (r = 0.231, P < 0.001) but was negatively correlated with 25(OH)D/24,25(OH)2D (r = -0.185, P < 0.01). Moreover, the total 25(OH)D, 25(OH)D3, 24,25(OH)2D, and 25(OH)D/24,25(OH)2D were correlated with 1,25(OH)2D. Furthermore, free 25OHD was positively correlated with creatinine (Cr) (r = 0.227, P <0.001). Our results showed a narrower distribution for free 25OHD than that reported by direct measurement techniques and confirmed the correlation between free 25OHD and total 25(OH)D.

中文翻译：

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基于LC-MS / MS的老年人中游离25OHD的分布。

维生素D缺乏症是所有年龄段的全球健康问题，尤其是在老年人口中。血清25（OH）D是评估维生素D营养状况的生物标志物。但是，游离激素假说提出，游离维生素D可能是维生素D营养状况的更可靠指标。因此，本研究的目的是（1）评估老年人中游离25OHD的分布，以及（2）评估游离25OHD与总25（OH）D，1,25（OH）2D，24之间的关联，25（OH）2D，钙（Ca），碱性磷酸酶（ALP）和磷（P）的老年人口。共有312名健康的老年人参加了这项研究，并收集了残留的血清样本。使用LC-MS / MS测量游离25OHD，总25（OH）D，24,25（OH）2D和1,25（OH）2D。使用自动分析仪测量其他生化分析物。我们的结果表明，随着总25（OH）D含量的增加，25（OH）D3、1,25（OH）2D，24,25（OH）D和游离25OHD的含量增加，而25（OH）D / 24,25（OH）2D含量下降。此外，我们观察到游离25OHD的水平与总25（OH）D（r = 0.226，P <0.001），25（OH）D（r = 0.221，P <0.001）和24显着正相关， 25（OH）2D（r = 0.231，P <0.001），但与25（OH）D / 24,25（OH）2D呈负相关（r = -0.185，P <0.01）。此外，总25（OH）D，25（OH）D3、24,25（OH）2D和25（OH）D / 24,25（OH）2D与1,25（OH）2D相关。此外，游离的25OHD与肌酐（Cr）呈正相关（r = 0.227，P <0.001）。