Wilcox Rand R, Granger Douglas A, Szanton Sarah, Clark Florence
Dept. of Psychology, University of Southern California, United States.
Institute for Interdisciplinary Salivary Bioscience Research (IISBR) Arizona State University, United States.
Physiol Behav. 2014 Apr 22;129:11-6. doi: 10.1016/j.physbeh.2014.02.012. Epub 2014 Feb 22.
Cortisol and dehydroepiandrosterone (DHEA) are considered to be valuable markers of the hypothalamus-pituitary-adrenal (HPA) axis, while salivary alpha-amylase (sAA) reflects the autonomic nervous system. Past studies have found certain diurnal patterns among these biomarkers, with some studies reporting results that differ from others. Also, some past studies have found an association among these three biomarkers while other studies have not. This study investigates these patterns and associations in older adults by taking advantage of modern statistical methods for dealing with non-normality, outliers and curvature. Basic characteristics of the data are reported as well, which are relevant to understanding the nature of any patterns and associations.
Boxplots were used to check on the skewness and presence of outliers, including the impact of using simple transformations for dealing with non-normality. Diurnal patterns were investigated using recent advances aimed at comparing medians. When studying associations, the initial step was to check for curvature using a non-parametric regression estimator. Based on the resulting fit, a robust regression estimator was used that is designed to deal with skewed distributions and outliers.
Boxplots indicated highly skewed distributions with outliers. Simple transformations (such as taking logs) did not deal with this issue in an effective manner. Consequently, diurnal patterns were investigated using medians and found to be consistent with some previous studies but not others. A positive association between awakening cortisol levels and DHEA was found when DHEA is relatively low; otherwise no association was found. The nature of the association between cortisol and DHEA was found to change during the course of the day. Upon awakening, cortisol was found to have no association with sAA when DHEA levels are relatively low, but otherwise there is a negative association. DHEA was found to have a positive association with sAA upon awakening. Shortly after awakening and for the remainder of the day, no association was found between DHEA and sAA ignoring cortisol. For DHEA and cortisol (taken as the independent variables) versus sAA (the dependent variable), again an association is found only upon awakening.
皮质醇和脱氢表雄酮（DHEA）被认为是下丘脑 - 垂体 - 肾上腺（HPA）轴的重要标志物，而唾液α - 淀粉酶（sAA）反映自主神经系统。过去的研究发现这些生物标志物存在一定的昼夜模式，但一些研究报告的结果与其他研究不同。此外，过去一些研究发现这三种生物标志物之间存在关联，而其他研究则未发现。本研究利用现代统计方法处理非正态性、异常值和曲率，对老年人中的这些模式和关联进行调查。还报告了数据的基本特征，这与理解任何模式和关联的性质相关。
使用箱线图检查偏度和异常值的存在，包括使用简单变换处理非正态性的影响。利用旨在比较中位数的最新进展研究昼夜模式。在研究关联时，第一步是使用非参数回归估计器检查曲率。基于所得拟合，使用一种稳健回归估计器，该估计器旨在处理偏态分布和异常值。
箱线图表明分布高度偏态且存在异常值。简单变换（如取对数）未能有效解决此问题。因此，使用中位数研究昼夜模式，发现与一些先前研究一致，但与其他研究不同。当DHEA相对较低时，发现觉醒时皮质醇水平与DHEA之间存在正相关；否则未发现关联。发现皮质醇与DHEA之间的关联性质在一天中会发生变化。觉醒时，当DHEA水平相对较低时，发现皮质醇与sAA无关联，但在其他情况下存在负相关。发现觉醒时DHEA与sAA呈正相关。觉醒后不久及当天剩余时间，忽略皮质醇时，未发现DHEA与sAA之间存在关联。对于DHEA和皮质醇（作为自变量）与sAA（因变量），同样仅在觉醒时发现存在关联。
