Garland M, Morris J S, Rosner B A, Stampfer M J, Spate V L, Baskett C J, Willett W C, Hunter D J
Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts 02115.
Cancer Epidemiol Biomarkers Prev. 1993 Sep-Oct;2(5):493-7.
We assessed the reproducibility over a 6-year period of 16 trace elements measured in toenails by comparing levels in paired specimens collected in 1982-1983 and 1988 from 127 women in the United States. The Spearman correlation coefficients for the reproducibility of toenail levels of selenium and arsenic (both known to reflect intake of these elements) were 0.48 and 0.54. Correlations for other elements ranged from 0.26 (copper) to 0.58 (zinc). In utilizing biomarkers to assess exposure in epidemiological studies of cancer and other chronic disease, random within-person variability in exposure leads to attenuation of measures of association between exposure and disease. We demonstrate the effect of such variability on odds ratios from a hypothetical case-control study. For a true odds ratio of 3.0 (for a comparison of the highest quintile versus the remaining 4 quintiles of exposure) the odds ratios which would be observed in the presence of the degree of within-person variability demonstrated in this study were 2.15 for toenail arsenic and 1.67 for toenail copper levels. Toenail concentrations of certain trace elements are useful biomarkers of exposure in which a single sample is assumed to represent long-term exposure. However, substantial attenuation in measures of association may occur.
我们通过比较1982 - 1983年和1988年从美国127名女性中采集的配对趾甲样本中的含量，评估了6年间趾甲中16种微量元素测量结果的可重复性。已知反映这些元素摄入量的硒和砷的趾甲含量重复性的斯皮尔曼相关系数分别为0.48和0.54。其他元素的相关系数范围为0.26（铜）至0.58（锌）。在利用生物标志物评估癌症和其他慢性病的流行病学研究中的暴露情况时，个体内部暴露的随机变异性会导致暴露与疾病之间关联测量值的衰减。我们通过一项假设的病例对照研究展示了这种变异性对优势比的影响。对于真实优势比为3.0（用于比较最高五分位数与其余4个暴露五分位数）的情况，在本研究中所展示的个体内部变异程度存在时，趾甲砷的观察到的优势比为2.15，趾甲铜含量的优势比为1.67。某些微量元素的趾甲浓度是有用的暴露生物标志物，其中单个样本被假定代表长期暴露。然而，关联测量可能会出现大幅衰减。
