Biostatistics and Computational Biology Branch National Institute of Environmental Health Sciences, Mail Drop A3-03, P.O. Box 12233, Research Triangle Park, Durham, NC, 27709, USA.
Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA.
Sci Rep. 2024 Jan 19;14(1):1682. doi: 10.1038/s41598-023-50506-5.
Iron status is often assessed in epidemiologic studies, and toenails offer a convenient alternative to serum because of ease of collection, transport, and storage, and the potential to reflect a longer exposure window. Very few studies have examined the correlation between serum and toenail levels for trace metals. Our aim was to compare iron measures using serum and toenails on both a cross-sectional and longitudinal basis. Using a subset of the US-wide prospective Sister Study cohort, we compared toenail iron measures to serum concentrations for iron, ferritin and percent transferrin saturation. Among 146 women who donated both blood and toenails at baseline, a subsample (59%, n = 86) provided specimens about 8 years later. Cross-sectional analyses included nonparametric Spearman's rank correlations between toenail and serum biomarker levels. We assessed within-woman maintenance of rank across time for the toenail and serum measures and fit mixed effects models to measure change across time in relation to change in menopause status. Spearman correlations at baseline (follow-up) were 0.08 (0.09) for serum iron, 0.08 (0.07) for transferrin saturation, and - 0.09 (- 0.17) for ferritin. The within-woman Spearman correlation for toenail iron between the two time points was higher (0.47, 95% CI 0.30, 0.64) than for serum iron (0.30, 95% CI 0.09, 0.51) and transferrin saturation (0.34, 95% CI 0.15, 0.54), but lower than that for ferritin (0.58, 95% CI 0.43, 0.73). Serum ferritin increased over time while nail iron decreased over time for women who experienced menopause during the 8-years interval. Based on cross-sectional and repeated assessments, our evidence does not support an association between serum biomarkers and toenail iron levels. Toenail iron concentrations did appear to be moderately stable over time but cannot be taken as a proxy for serum iron biomarkers and they may reflect physiologically distinct fates for iron.
铁的状况在流行病学研究中经常被评估，由于趾甲采集、运输和储存方便，并且可能反映出更长的暴露窗口，因此是血清的一种替代物。很少有研究检查痕量金属的血清和趾甲水平之间的相关性。我们的目的是在横断面和纵向基础上比较血清和趾甲中铁的测量值。使用美国范围内前瞻性姐妹研究队列的一个子集，我们比较了铁、铁蛋白和转铁蛋白饱和度的血清浓度与趾甲中的铁测量值。在 146 名在基线时既捐献了血液又捐献了趾甲的女性中，一个亚组（59%，n=86）在大约 8 年后提供了标本。横断面分析包括趾甲和血清生物标志物水平之间非参数 Spearman 秩相关。我们评估了随时间变化的趾甲和血清测量值的个体内秩保持情况，并拟合混合效应模型以测量与绝经状态变化相关的随时间变化的变化。基线时（随访时）血清铁的 Spearman 相关系数为 0.08（0.09），转铁蛋白饱和度为 0.08（0.07），铁蛋白为-0.09（-0.17）。两次时间点之间趾甲铁的个体内 Spearman 相关系数高于血清铁（0.30，95%CI 0.09，0.51）和转铁蛋白饱和度（0.34，95%CI 0.15，0.54），但低于铁蛋白（0.58，95%CI 0.43，0.73）。在 8 年的时间间隔内经历绝经的女性中，血清铁蛋白随时间增加，而趾甲铁随时间减少。基于横断面和重复评估，我们的证据不支持血清生物标志物与趾甲铁水平之间的关联。然而，趾甲铁浓度似乎在随时间推移中度稳定，但不能作为血清铁生物标志物的替代品，它们可能反映了铁的生理上不同的命运。
