Endogenous cortisol in keratinized matrices: Systematic determination of baseline cortisol levels in hair and the influence of sex, age and hair color

https://doi.org/10.1016/j.forsciint.2017.12.032Get rights and content

Highlights

  • Baseline cortisol levels are generally low in hair.

  • A standardized analytical method for hair cortisol measurement is needed.

  • Hair cortisol is age dependent and influenced by sex and hair color.

  • Age-dependent normative baseline cortisol levels are highly recommended.

Abstract

The measurement of hair cortisol is increasingly used to measure long-term cumulative cortisol levels and investigate its role as an important stress mediator. In this study a comparative statistical analysis of five independent studies (all analyzed in our laboratory) was performed to investigate baseline ranges of cortisol values in hair and evaluate potential influences of sex, age and hair color. Cortisol concentrations in hair of 554 subjects were measured and a comparative statistical analysis was performed. The analysis showed that cortisol levels significantly differ depending on age. The toddler group (7 months (0.6 years) to 3 years) showed significantly higher values (median 10 pg/mg, p-value < 0.0001, d = 0.78) than the adolescent group. The adolescent groups showed significantly lower (p-value < 0.0001, d = 0.58 and p < 0.0001, d = 0.13) values (median 2.4 pg/mg and 2.8 pg/mg) than the adult group (median 5.8 pg/mg).

Furthermore, in the adult group men showed significantly higher cortisol values than women (p-value < 0.05, d = 0.17). This effect could not be seen in the adolescent group. Black hair showed higher cortisol concentrations than blond hair (p-value < 0.0001, d = 1.3). In addition, two rounds of interlaboratory comparisons for hair cortisol samples between four laboratories revealed very consistent results.

Our results demonstrate that baseline cortisol levels are generally low in hair thus making a standardized and well-elaborated analytical method indispensable for accurate determination. Age-dependent normative baseline cortisol levels (toddlers, adolescents and adults) are highly recommended based on the comparative analysis comprising five independent studies.

Introduction

Cortisol, one of the most important glucocorticoid hormones is synthesized in the adrenal cortex and is a frequently assessed marker in psychoneuroendocrine stress research. Cortisol has been measured mainly in saliva, serum or urine in recent years. Cortisol concentration in these matrices underlies a circadian rhythm which means the concentrations fluctuate during the day. Those matrices allow the analysis of acute dynamic cortisol changes. In contrast, the effects of chronic stress and its implications on health often require the assessment of long-term cortisol levels. The analysis of cortisol in hair has therefore been a major methodological advance as it provides a retrospective measure of cumulative cortisol levels over extended time periods up to several months.

Over the past decade, the validity of hair cortisol as a measure for long term cortisol secretion has been established and the usefulness of hair cortisol as a marker for chronic stress has been demonstrated [1]. It has also been shown that hair cortisol is associated with a range of pathological and/or psychological conditions, such as burnout, Cushing's syndrome, and mood and anxiety disorders [2], [3], [4]. Overall, these studies show that hair cortisol has a great potential in stress research but still further research is needed on fundamental aspects that might influence hair cortisol. The establishment of standardized measurements, the definition of established values (e.g. baseline cortisol levels in untreated hair samples) and knowledge of potential confounding variables such as age, sex and hair color are important prerequisites for the establishment of hair cortisol as a biological marker in the future.

To propose established values, the quality of the analytical method used to measure hair cortisol is of great importance. Mainly immunoassay and LC–MS/MS based protocols have been used so far, revealing highly variable results [5], [6]. Previous research has also repeatedly shown that age has an influence on hair cortisol, albeit with varying results [5], [7]. The main research has been done on specific age groups, like young children or adults and older adults [8]. So far, there is only very limited information on hair cortisol levels in adolescents which is an age group that is very interesting due to changes in the pubertal hormone status. Previous research has also revealed highly heterogeneous findings with respect to sex differences [1]. Several studies have failed to show sex differences but newer studies imply that there are such differences [5]. The effect of natural hair color on cortisol concentration has also been studied but has mostly been found not to be correlated. Some newer literature however does show some association [9] and further investigations are needed to clarify this.

In summary, existing research has identified hair cortisol as a potential biological marker for chronic stress. However, the lack of standardized methods and inconsistent findings demonstrate the need to harmonize measurements and establish value ranges for cortisol in hair. This study was undertaken to address these gaps in research and to try to determine baseline cortisol levels in toddlers, adolescents and adults. Furthermore, the influence of sex and hair color on hair cortisol concentrations has been investigated to further clarify the influence of these variables and an interlaboratory comparison was performed to standardize analytical methods for cortisol measurements in hair.

Section snippets

Subjects

554 subjects from control groups of five independent studies representing the general healthy population of Switzerland and Australia were enrolled in this study. 374 adolescents were included from the “Brisbane Longitudinal Twin Study” [10], [11], 101 adults were included from the “Contact to Nature study” [30], 35 adults were included from the control group investigated within the “Zurich Cocaine Cognition Study” (ZuCo2St) [12], 30 adults from the study “Neurobiological Adaptations and

Age

To investigate the influence of age on hair cortisol the entire study group was first divided into four different age groups: 7 months to 3 years (toddlers), 12–13 years old adolescents (adolescents 1: pre-pubertal), 14–17 years old adolescents (adolescents 2: post-pubertal) and 18–70 years old (adults). Kruskal–Wallis analysis revealed that there was a significant difference between the toddler group and adolescent sub-group 1 (p < 0.0001, d = 0.9) and adolescent sub-group 2 (p < 0.0001, d = 0.56).

Discussion

In recent years, hair cortisol has emerged as a non-invasive measure for long-term hypothalamus-pituitary-adrenal (HPA) axis activity. However, previous research has been limited by the lack of well-established normative values for cortisol in adolescents and adults. Numerous studies have been performed in the past that show large deviations in hair cortisol baseline values [6]. One explanation for this fact might be the use of the analytical method. Previously, immunoassay based methods

Acknowledgment

We thank all the laboratories for participating in the interlaboratory comparison.

Funding for the collection of Australian hair samples was provided by Australian NHMRC (National Health and Medical Research Council (AU); grants APP1049911 and APP1009064). Hair cortisol assays of the Australian hair samples were funded by a grant from the German Federal Ministry of Education and Research (BMBF), through the Integrated Network IntegraMent (Integrated Understanding of Causes and Mechanisms in

References (30)

  • C. Kirschbaum et al.

    Hair as a retrospective calendar of cortisol production – increased cortisol incorporation into hair in the third trimester of pregnancy

    Psychoneuroendocrinology

    (2009)
  • V.L. Wester et al.

    Scalp hair cortisol for diagnosis of Cushing's syndrome

    Eur. J. Endocrinol.

    (2017)
  • M. Penz et al.

    Hair cortisol as a biological marker for burnout symptomatology

    Psychoneuroendocrinology

    (2017)
  • L. Dettenborn et al.

    The assessment of cortisol in human hair: associations with sociodemographic variables and potential confounders

    Stress

    (2012)
  • L. Rietschel et al.

    Hair cortisol in twins: heritability and genetic overlap with psychological variables and stress-system genes

    Sci. Rep.

    (2017)
  • Cited by (48)

    • Cortisol: Analytical and clinical determinants

      2023, Advances in Clinical Chemistry
    View all citing articles on Scopus
    View full text