Overview: The stress hormone cortisol, secreted mainly from the adrenal gland, can be measured in various matrices, including blood, saliva, urine, and more recently hair. The method of choice depends on the time window of interest and the research question. Plasma and salivary cortisol samples reflect “snapshots" of recent hypothalamic pituitary adrenal (HPA) axis activity, reflecting cortisol activity over seconds to minutes prior to collection. Urinary cortisol samples provide insight into the time window of collection ranging from overnight to 24-hour periods. In contrast, hair cortisol provides a window on longer-term (months) cortisol exposure levels. Here we focus on hair cortisol, as a measure of long-term HPA activity that is relatively easy to implement in field and population-based studies of aging.
Background: Assessment of cortisol in hair is a recent method that quantifies cumulative cortisol production over extended periods of time (up to 6 months), suggesting that hair cortisol may be a unique biomarker of long-term HPA axis activity. Cortisol is incorporated into the hair as it grows (Pragst & Balíková, 2006) and measurement of cortisol levels within a specific hair segment reflects integrated, cumulative cortisol secretion within that hair growth period. Scalp hair growth is variable, but an average rate of 1 cm per month has been generally accepted (Harkey, 1993; Pragst & Balíková, 2006; Wennig, 2000). Thus, a proximal (scalp-close) 1–cm hair segment reflects total cortisol secretion in the last month, the second proximal 1–cm segment represents the cortisol production in the month before that and so on. Several studies have validated hair cortisol measurement, linking hair cortisol concentrations to repeated measures in saliva and urine, and studying hair cortisol concentrations in patients with endocrine disorders, such as hyper- or hypocortisolism (for reviews see Gow, Thomson, Rieder, Van Uum, & Koren, 2010; Russell, Koren, Rieder, & Van Uum, 2012). Hair cortisol has also been linked to chronic stress exposures and mental health conditions (Stalder et al., 2017; Staufenbiel, Penninx, Spijker, Elzinga, & van Rossum, 2013). It is higher in pregnancy, as expected (Kirschbaum, Tietze, Skoluda, & Dettenborn, 2009). It can be measured in newborns, and may be lower in newborns with preterm birth (Hoffman, D'Anna-Hernandez, Benitez, Ross, & Laudenslager, 2017).
Collection and Measurement: Hair collection is described in detail here: http://gero.usc.edu/CBPH/network/resources/hair.html
Unfortunately, the link only describes hair collection for participants with long hair and does not give instructions for individuals with shorter hair. However, researchers with expertise in hair cortisol collection are often willing to share their knowledge with investigators
For more information on collecting hair samples for hair cortisol analysis in African Americans see (Wright et al., 2018): https://www.jove.com/video/57288/collecting-hair-samples-for-hair-cortisol-analysis-african
Strengths: Hair cortisol analysis advances neuroendocrine research for several reasons.
1) It provides a cumulative and retrospective measure of systemic cortisol secretion for periods up to 6 months (after which cortisol tends to decrease in hair), a time period previously difficult or impossible to capture (Kirschbaum et al., 2009). This makes it an ideal biomarker when studying allostatic load, including the effects of chronic psychological stress.
2) It is a non-invasive, painless method that allows easy and field-friendly sample collection by non-professionals.
3) Hair samples do not decompose like body fluids, which makes longer-term storage at room temperature feasible.
4) Hair cortisol likely reflects free, unbound cortisol, and is thus less susceptible to typical confounds such as oral contraceptive usage, as in salivary/serum cortisol research (Dettenborn, Tietze, Kirschbaum, & Stalder, 2012).
1) Interpretation of hair cortisol levels is complex, because cumulative cortisol secretions are a function of multiple, potentially interacting factors, including chronic stress experiences, genetic dispositions, developmental experiences, and altered receptor sensitivities in brain structures that shape its release. To meaningfully interpret hair cortisol levels, information on chronic stress is needed, ideally in combination with genetic and early developmental information.
2) Cumulative cortisol levels are crude averages across time and thus do not inform about regulation of the HPA axis diurnal rhythms (cortisol awaking response, nadir at night) or peak stress reactivity.
3) A major limitation in hair cortisol research is the use of different analysis methodologies across different laboratories. Most labs tend to use traditional immunoassay methods (vs. liquid chromatography/mass spectrograph), which are relatively easy to conduct. But intra assay variability is generally 9-12% but can be addressed by processing samples in a manner that balances for conditions or maintains all a participant’s samples on the same assay plate. Different assay method such as ELISA, RIA, and HPLC/MS make comparison of levels of steroid difficult. Currently, there is no gold standard technique for cortisol extraction and analysis. Reference values of hair cortisol of typical groups have not yet been determined (Staufenbiel et al., 2013; Russell, et al., 2015).
3) To date, there is little available information on fundamental aspects that can inﬂuence hair cortisol concentrations. Therfore, acceptable co-variates are not well understood (e.g., frequency of hair washing, coloring, type of shampoo use, insufficient hair growth; age, ethnicity, sex). Effects of hair washing may be responsible for the decline in cortisol concentrations from scalp-near hair segments to more distal hair segments, which have been reported by some (e.g., Gao et al., 2010; Kirschbaum et al., 2009) but not all studies (e.g., Dowlati et al., 2010; Thomson et al., 2010). Additionally, it is unknown exactly how cortisol is incorporated into the hair. Four models have been proposed (Pragst & Balíková, 2006) a) Active or passive diffusion from blood into cells of the hair follicle, b) Diffusion from body secretion (e.g., sweat) during formation of the hair shaft, c) Incorporation from deep skin compartments during hair shaft formation, d) External environmental sources after hair shaft formation, but further experimental research is needed. Importantly the impact of stress of hair growth is not clear by could influence levels measured. Additionally, the medical use of topical, oral, injected, eye drops, and intranasal administration or medication containing cortisol, or an allied steroid will affect levels assessed in hair. Growth rates are also affected by racial origin and need to be considered in large mixed population studies. The impact of age is largely unknown.
Author and Reviewer(s)
This summary was prepared by Drs. Stefanie Mayer and Rachel Radin. Reviewed by Drs. Clemens Kirschbaum and. Mark Laudenslager. Please direct suggestions and feedback to [email protected]. Version date: February 2, 2018.
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