A preliminary study of steroid reproductive hormones in human hair

Non-invasive wool hormone assessment of Australian merino rams (Ovis aries): a pilot investigation of cortisol and testosterone

Introduction

Non-invasive hormone assessment is growing in interest as producers and livestock researchers seek new methods to assess animal welfare. Non-invasive wool assessment offers long-term, historic reflections of hormone concentration at the scale of weeks and months - and are not limited by sampling stress - thus making wool an appropriate tissue for long-term hormone analysis. This pilot study quantified cortisol and testosterone concentrations of ram fleece and determined if there is a significant difference between segments of the sample staple, and whether there is a correlation between hormones. Cortisol is a glucocorticoid produced within the adrenal glands and secreted in anticipation of or in response to a stressor. Testosterone is an androgen mainly synthesised within the testes of males and responsible for several critical functions including regulation of muscle growth, libido and spermatogenesis.

Methods

In our study, 70 topknot wool samples were collected from rams on a commercial stud property in Dirranbandi, Queensland, Australia. Of these animals, 12 samples were selected at random to undergo cortisol and testosterone quantification. In the laboratory, a single, intact staple was isolated from the total sample, divided into 10 mm segments and prepared for their respective (cortisol or testosterone) immunoassays.

Results

No significant difference (p > 0.05) was found between wool segments for either cortisol or testosterone, however, statistical differences (p < 0.05) were found between individuals for both hormones. A strong positive correlation (R2 = 0.9173, p < 0.05) was found between wool cortisol and testosterone concentrations.

Discussion

In summary, this study reveals the major future possibilities for non-invasive wool hormone assessment in merino rams.

Sense of coherence, mental health, and hair cortisol concentrations among older people during the COVID -19 pandemic: a cross-sectional study

BACKGROUND

A person's sense of coherence (SoC) is likely to affect coping when exposed to a life changing event like the COVID -19 pandemic, which impacted the older population especially hard, an age group that already suffers from a lot of mental illness. Thus, the aim of this study was to investigate the associations between SoC and mental health in older adults using both screening scales and hair cortisol concentrations (HCC).

METHOD

A cross-sectional design studying a cohort of 70-80 years old, N = 260, set in Swedish primary care during the pandemic years 2021-2022. Instruments used are sense of coherence 13 (SoC-13), EQ-5D-3L, Geriatric depression scale 20 (GDS-20), Hospital anxiety and depression scale (HADS), and Perceived stress scale 10 (PSS-10). Sociodemography and factors concerning SoC, and mental health are explored. HCC are measured using radioimmunoassay. Outcome measures are factors independently associated with SoC. Linear regression models were performed with SoC as dependent variable, and priory path analyses explored whether associations with SoC were direct, or indirect via anxiety.

RESULTS

SoC was significantly associated with anxiety (p < 0.001), perceived economic status (p = 0.003), belief in the future (p = 0.001), and perceived negative mental effect from the COVID -19 pandemic (p = 0.002). The latter was 96% indirectly associated with SoC (p < 0.001), whereas perceived economic status together with belief in the future was 82% directly associated with SoC (p = 0.17). HCC and sex were not significantly associated with SoC, but, noticeably, high HCC was equally distributed between women and men. Women reported significantly lower quality of life (p = 0.03), and more symptoms of anxiety (p = 0.001) and depression (p < 0.001).

CONCLUSION

Anxiety, belief in the future, perceived negative effect on mental health due to the pandemic, and perceived economic status were significantly associated with SoC. Anxiety is suggested to be important in explaining the association between perceived negative mental effect from the COVID-19 pandemic and SoC. Women reported significantly poorer mental health and life quality than men.

Hair cortisol levels in cats with and without behavioural problems

OBJECTIVES

The aim of the study was to analyse hair cortisol levels in cats whose owners had reported behavioural problems and undesirable behaviour. In addition, feline hair cortisol levels were compared between sexes, for indoor and outdoor cats and also for cats living in single or multi-cat households.

METHODS

In total, 55 cats participated in the study, including 31 females and 24 males from various households. The cats belonged to 25 different owners who answered a questionnaire survey. The biological material used for the research were 2-3 cm fragments of hair removed at the level of the skin with scissors by the owners from the cats' lumbosacral area. The cortisol concentration in the samples was determined with the DRG Salivary Cortisol HS ELISA. Statistical analysis of the results was performed with Statistica 13.3.

RESULTS

A tendency toward lower cortisol levels was found in outdoor cats vs indoor cats (U = 251.5, P = 0.066). It was also found that the cats exhibiting behavioural problems (eg, house soiling [eliminating outside the litter box]) or aggressive behaviour towards household members had statistically significantly higher hair cortisol levels (U = 162.0 [P = 0.027] and U = 9.0 [P = 0.040], respectively).

CONCLUSIONS AND RELEVANCE

High levels of stress in cats can affect their interactions with other cats and with humans. The incidence of undesirable behaviour was observed more frequently in indoor cats. Significantly higher cortisol levels were found in cats that eliminated outside the litter box or that showed aggression towards their owners.

Impact of hair type, hair sample weight, external hair exposures, and race on cumulative hair cortisol

The biomarker cortisol assesses the impact of biopsychosocial stressors that activate the stress response system. Hair has emerged as a valid and non-invasive means of gauging cumulative cortisol deposited over month-long periods of time. Established protocols for the extraction of hair cortisol are being validated and refined in humans, yet methodological information about hair characteristics on cortisol remains limited. In addition to external hair exposures (e.g. dye, time spent outside), we examined hair categorization or type (e.g. kinky, straight) by extending a hair typing methodology for scientific use that is currently popular among hair care professionals. We then examined the interaction between hair type and race on cortisol levels with a hair questionnaire. Three studies were pooled to investigate how sample weight, hair type, race, heat exposures, and hair treatments impacted cumulative hair cortisol concentrations. Study 1 consisted of Adult Kenyan Medical Workers (N = 44); Study 2 Mexican and Mexican Americans (N = 106); and Study 3 American Youth (N = 107). We found significantly higher cortisol in 5 mg of hair when compared to larger sample weights, and higher cortisol in those who spent more time outdoors. Cortisol concentrations differed between racial groups and varied by hair type; moreover, there were directional differences in cumulative cortisol from straighter to curlier hair types which depended on racial group. In addition to demonstrating the impact of relatively novel control factors like hair sample weight, outdoor exposure, and hair type, the present study illustrates the importance of disentangling hair type and race to understand variability in cumulative hair cortisol. These influences should be included in future studies that measure hair cortisol.

Scalp hair sweating as a predictor of hair cortisol level in human compared to obesity and other confounders

Inconsistent results were found throughout the literature regarding factors affecting hair cortisol levels. Hair cortisol level in humans was not studied for its associations to scalp hair sweating or hair wash frequency in a patient-based way. Factors affecting hair cortisol levels must be precisely known in order to interpret the results correctly. The aims of the study are to assess if BMI, Perceived Stress Scale (PSS), hair wash frequency, and sweating with scalp hair affect hair cortisol levels. It will assess which of these factors are more significant predictors of hair cortisol levels. In a study on healthy adults, information about history, socio-demographics, PSS, hair wash frequency, hair treatment, and scalp hair sweating were collected, and hair samples were taken and analyzed for their hair cortisol level. Associations of hair cortisol levels with each of the variables were investigated and significant predictors of hair cortisol levels among the variables were found. Mean hair cortisol level in the study participants was 16.84 pg/mg hair. Hair cortisol has a significant positive association with weight, BMI, PSS, and scalp hair sweating, p < 0.05. Scalp hair sweating significantly predicts hair cortisol levels by 12.3%, while other variables did not significantly predict hair cortisol levels, p < 0.05. Scalp hair sweating significantly predicts hair cortisol levels. Age, hair wash frequency, hair treatment, and stressful events have no associations with hair cortisol levels. Although BMI and PSS are associated with hair cortisol levels, they do not significantly predict it. Obesity is significantly associated with profuse sweating, thus the increase in hair cortisol levels in obese individuals could partly be the result of a higher incidence of sweating in these individuals. Thus, scalp hair sweating should be taken into consideration during the study and interpretation of hair cortisol levels.

Effects of person-environment fit of gender-role orientation on burnout, engagement and hair steroids as stress biomarkers among women

BACKGROUND

Analysis on gender related differences in occupational stress and burnout levels usually reveal higher occupational stress and burnout levels for women compared to men, especially in male-dominated working environments. In opposition to group differentiation, more specific gender-related dimensions feminity and masculinity were used in the study to describe individual and work environment characteristics and analyze their effects.

METHODS

In a cross-sectional design, survey results were linked to steroid levels in hair samples. Data was collected in a German medical services company with 146 employed women age 22-66 years (M = 40.48, SD = 10.38), 58 of them provided hair samples for steroid detection. Feminity and masculinity were measured by Gender Role Orientation Scale GTS+. Two Person-Environment fit scores in feminity and masculinity were calculated by subtracting individual from environment values. Both fit scores were proved as predictors in hierarchical linear regression models predicting burnout and work engagement as well as hair steroids cortisol, cortisone, DHEA, testosterone and progesterone detected by Liquid Chromatography-Mass Spectrometry (LC-MS/MS) as stress biomarkers. Bivariate correlations as well as moderator and mediator analysis were implemented.

RESULTS

After considering age, role clarity, and work organization, Person-Environment fit in feminity still added significant variance explanation (β = .23, ∆ R2 = .05, p = .003) for burnout. Person-Environment fit in feminity also explained poor variance in work engagement (β = -.29, R2 = .09, p < .001). Person-Environment fit in masculinity added considerable variance explanation (β = .34, ∆ R2 = .12, p = 0.018) to cortisol levels after including quantitative demands to the model.

CONCLUSIONS

Person-Environment fit in feminity might be inspected as a predictor for burnout and work engagement. Person-Environment fit in masculinity can be taken into consideration as a predictor for hair cortisol as stress biomarker. Feminity and masculinity can be used as personality traits as well as characteristics of work environment, thus providing a particular gender-role related method of differentiation within gender groups. Also, specific methods could be derived for stress and burnout prevention and promotion of work engagement. Representative population studies with bigger samples and longitudinal surveys are needed to better explore the benefits and limitations of this approach.

Within-person changes of cortisol, dehydroepiandrosterone, testosterone, estradiol, and progesterone in hair across pregnancy, with comparison to a non-pregnant reference group

The literature on hormone changes in pregnancy has focused largely on cortisol, and changes in sample average concentrations. Within-person changes and variability in hormone concentrations are less commonly reported, particularly for sex hormones, and especially measured in hair. Using a prospective sample of pregnant women and a non-pregnant comparison group, we examined changes in five steroid hormones in hair. Non-pregnant women were recruited from the same area with parallel procedures and assessment timeline. Participants include 68 women (34 pregnant, average age ​= ​29.14, and 34 non-pregnant; average age ​= ​27.18) who were predominately non-Hispanic White (83%), and above the 2020 poverty line (75%). Pregnant women provided 3 ​cm hair samples and completed questionnaires three times during pregnancy: 1) at 12 weeks, 2) at 26 weeks, and 3) at 38 weeks. Non-pregnant women provided 3 ​cm hair samples and completed questionnaires three times, at baseline, 14 weeks later, and 12 weeks after that to mirror the assessment schedule of the pregnant group. There was clear evidence that progesterone was higher initially and increased dramatically across pregnancy whereas non-pregnant patterns showed no systematic change. There was suggestive evidence that cortisol and estradiol increased over pregnancy and in non-pregnant women similarly across the same time course. There was suggestive evidence that DHEA decreased across pregnancy, particularly early in pregnancy, differently from patterns in non-pregnant women over the same time course. Most importantly, there was substantial variability of hormone concentrations and many different within-person patterns of changes in these hormones over time, with little evidence of systematic change or stability within-individuals. Moving beyond discussing sample averages to including within-person and non-linear changes in studies of hormones-behavior associations during pregnancy is an important future direction for further investigation.

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We describe within-person hormone changes in pregnant and non-pregnant women.

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There were many observed patterns of change over time within individuals.

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Average hair progesterone increased and DHEA decreased across early pregnancy.

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Average hair cortisol and estradiol weakly increased in both groups of women.

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There was far more variability over time than systematic change or stability.

Hair Cortisol Concentration as a Biomarker of Sleep Quality and Related Disorders

Cortisol is the end product of the hypothalamic-pituitary-adrenal (HPA) axis, and its production is increased mainly in stressful situations or in chronic disorders accompanied by stress enhancement. Altered cortisol concentrations have been reported in a number of neuropsychiatric diseases and sleep disorders. Cortisol concentrations have been measured using several methods, and in several matrixes, such as blood, saliva, and urine. However, lately, hair cortisol, for several reasons, has emerged as a promising biomarker of long-term retrospective HPA activation. Several experimental approaches for cortisol measurement with the corresponding concentration reference ranges and a summary of findings from scientific literature on this field are presented. There is evidence of a close relationship between HPA functional alteration and the development of neuropsychiatric disorders. Sleep disorders are the most common manifestation in several neuropsychiatric conditions, and have also been associated to cortisol alterations in both adults and children. Many studies indicate that hair cortisol constitutes a valuable tool for further contributing to existing data on salivary, plasma, or urinary cortisol concentrations in patients with sleep disorders.

Exploring the Utility of Hair Endocannabinoids for Monitoring Homeostasis in Bonobos

AbstractQuantifying physiological challenges has gained increasing importance in evolutionary biology, behavioral physiology, and conservation. One matrix that is particularly useful for obtaining long-term records of physiological changes in mammals is hair. Potential markers are components of the endocannabinoid (EC) system, which regulates homeostasis of the brain as well as the endocrine and immune systems. Here, we present results from the first study to measure ECs (anandamide [AEA], 2-archidonyl glycerol [2-AG]) and EC-like compounds (N-palmitoylethanolamine [PEA], N-oleoylethanolamine [OEA], N-stearoylethanolamine [SEA]) in the hair of a nonhuman primate. We found that AEA, SEA, PEA, and OEA can be reliably measured in hair samples. When comparing the measurements of hair from different body parts, we found that variations of some analytes suggest that hair location is likely to affect results. For changes in health status, measurements of ECs and EC-like compounds reflected differences at both intra- and interindividual levels. We concluded that the EC system potentially provides novel tools to assess well-being, health status, and metabolic stress-not only in the hair of humans but also in that of domestic and wild animals. Measuring changes in ECs and EC-like compounds may improve the long-term monitoring of health status in captive and wild primates and may serve as a useful measure in animal welfare programs.

Reproductive hormone measurement from minimally invasive sample types: Methodological considerations and anthropological importance

Energetic investment in human reproduction has long been recognized as costly, influencing developmental, physiological, and behavioral patterns in males and females. These effects are largely coordinated through the actions of reproductive hormones (eg, testosterone, estradiol, and progesterone). Here, the utility and limitations of minimally invasive sampling techniques are explored, providing a novel perspective on how reproductive hormone measurements can enhance reproductive endocrinology research. Salivary steroid measures are most commonly used, although several dried blood spot and urine assays are also available, and researchers continue to explore the efficacy of other sample types. These relatively simple measures have facilitated the collection of multiple samples from a single participant, allowing researchers to more accurately track the diurnal and cyclical variation exhibited by many reproductive hormones. Ultimately, the ability to collect fine-grained participant data allows biological anthropologists to better test questions central to human reproductive ecology, life history theory, and public health. For example, fieldwork using these techniques suggests that testosterone profile variation across populations is influenced by energetic constraints and reproductive status. Moreover, hormone concentrations shape the development of sex characteristics, with implications for evolutionary questions related to sexual selection. Hormone levels also can be used to identify a range of medical concerns (eg, suppressed hormone production levels linked with psychosocial stress). These findings highlight how minimally invasive collection techniques can be applied to test diverse evolutionary hypotheses and identify important health concerns. Still, more work is needed to standardize collection and laboratory analysis procedures, thereby enabling more direct data comparisons between researchers.

Hair as an alternative noninvasive matrix: sources of variation in testosterone levels

Hair is one widely used alternative matrix for endocrine studies. Not only can it maintain hormone content during storage for long periods of time, but its collection also induces little to no stress. Noninvasive techniques have broadened the opportunities for endocrine research, particularly regarding wild animals. Despite its advantages, many sources of variation may affect the steroid concentration found in hair, such as body location harvested, fur color, reproductive status, and sex. Thus, domestic species, such as the dog, are an excellent and approachable model for understanding this variability. For such, we addressed diverse sources of variation in testosterone concentrations from 24 domestic dogs (Canis lupus familiaris) of the Poodle breed of various colors and neuter status, and from both sexes. The variation comprised the comparison between 2 different matrices (blood vs hair); 2 different extraction storage methods (refrigerator vs freezer); 3 body regions (head, torso, and limbs); 3 coat colors (black, brown, and white); different neuter status (intact vs castrated males) and, finally, sex. Our results showed no correlation between blood and hair testosterone concentrations. Additionally, we did not find differences related to the storage method, body region, or coat color. There were differences in concentration between males and females, but not between females and castrated males. We discuss hair testosterone levels exhibited reasonable stability, and we present practical applications for both domestic and wildlife animals.

Sheep wool cortisol as a retrospective measure of long-term HPA axis activity and its links to body mass

Hair cortisol analysis has been suggested as a powerful retrospective measure of long-term hypothalamic-pituitary-adrenal (HPA) axis activity in numerous mammal species. In contrast, research evaluating the use of wool as a marker of long-term HPA axis activity is still scarce, and wool differs from hair in a number of ways. Here, we assess repeatability and differences in wool cortisol concentrations (WCCs) across (i) the wool shaft, (ii) two body locations, and (iii) time, in 33 barren Welsh mountain ewes (Ovis aries). We also (iv) investigated effects of grazing-related changes in body mass on WCCs and (v) assessed effects of the washing procedure during sample preparation on WCCs. Cortisol concentrations were repeatable but differed significantly across the wool shaft indicating that, provided wool growth rate is known, a single sample per individual could be used as a retrospective cortisol "timeline." WCCs were significantly higher in shoulder than in back samples, and no correlation between these two body locations was found, highlighting the importance of sampling from the same body location for repeated measures. An increase in body mass during grazing corresponded with a decrease in WCCs, which was significantly negatively correlated with body mass (and positively with age), suggesting that WCCs can be used as a marker of body condition and nutritional status in sheep. Interestingly, we found higher WCCs in washed compared with unwashed samples and discuss implications of this finding for future work. Overall, our study revealed significant within- and between-individual differences in WCCs and highlights a number of advantages but also methodological considerations of using WCCs as a retrospective measure of long-term HPA axis activity in sheep.

Hair Cortisol in Sheltered Cows and Its Association with Other Welfare Indicators

India, the country with the largest population of dairy cows in the world, has a policy of retiring abandoned and non-lactating cows in shelters, but the level of provision for their welfare in these shelters is unclear. Cows in 54 shelters across India were assessed for historic evidence of physiological stress, through determination of hair cortisol in 540 samples from 10 cows in each shelter by enzyme immunoassay. Animal-based and shelter resource-based welfare measures were recorded and correlations with the hair cortisol investigated by multivariable analysis. High hair cortisol concentrations were associated with dung in the lying area of the cowshed, a low dry bulb temperature there and little cow access to yards, as shelter-based variables. At a cow level, high hair cortisol concentrations were associated with dirty flanks, hock joint ulceration, carpal joint injuries, body lesions, dehydration, an empty rumen, old age, and low levels of body hair loss. Hair cortisol level promises to be an effective biomarker of stress in cows when conducting studies under field conditions.

Assay validation of hair androgens across the menstrual cycle

INTRODUCTION

Saliva is a common noninvasive biofluid for measuring stress and sex hormones, yet one pressing limitation is that salivary hormones fluctuate momentarily, daily, and (for girls) across the menstrual cycle. Hair steroid assays are thought to provide a cumulative index which collapses across hormonal variability, potentially eliminating the confound of daily and menstrual cyclicity and thereby reflecting individual differences in average hormone levels. Here we seek to validate a hair bioassay methodology and test whether hair androgens accurately measure long-term, stable androgen levels in emerging adult women across two menstrual cycles.

METHODS

Hair samples were collected at the end of each menstrual cycle for two cycles, and saliva samples were collected in the morning once per week across two menstrual cycles (N = 11 women). Hair samples were segmented by 1 cm for the first 4 cm to reflect the hormone levels of the past four serial months. Hair samples were assayed using commercially-available enzyme-immuno-assays for testosterone and DHEA.

RESULTS

Hair androgen concentrations were significantly correlated with averaged saliva hormone levels (DHEA: r = .75, p < .05; Testosterone: r = .67, p < .05). With respect to hair hormone stability, there were significant correlations for almost all the pairs of two 1 cm hair segments collected in two months that corresponded to the same time period. Hair androgens in one segment were significantly correlated with those in next segment. Regarding salivary androgen stability, the intra-class correlation across the weekly saliva samples indicated that for DHEA 59% of the total variance was within person and 41% was between person; and for testosterone 91% of the total variance was between person, and only 9% within person.

DISCUSSION

Results suggest that a one-time measure of hair provides a valid and reliable estimate of average steroid levels across two months. Moreover, whereas saliva measures of androgen levels capture week-to-week fluctuations in steroids, hair samples provide information on individual differences in average exposure to steroids, across long periods of time, such as months. Results are encouraging that hair DHEA and testosterone reflects the cumulative hormonal concentration and can be used as a stable hormonal index. Results also indicate that it is feasible to collect the first 3-4 centimeters of hair for studies of stable hormone levels.

Hair cortisol concentrations in a Spanish sample of healthy adults

BACKGROUND

Hair cortisol concentration (HCC), as a novel promising method to retrospectively measure hypothalamic-pituitary-adrenal (HPA) axis activation, is being increasingly studied. We tested the relationships between HCC and a range of possible confounding variables in a Spanish sample of healthy adults and pregnant women.

METHODS

The number of healthy adults who participated in the study was 529, being 270 males and 259 females, with a combined mean age of 37.88 years (SD = 15.66). Additionally, a separate sample of 62 pregnant women was also recruited with a mean age of 32.95 (SD = 3.67), and in the first trimester of pregnancy. Each participant was interviewed before the study to obtain sociodemographic and lifestyle variables, and a hair sample was taken from the posterior vertex of the head, cut as close to the scalp as possible. Assuming the average growth rate of head hair is 1 cm per month, a 3-cm segment was analysed, in order to measure the cortisol concentrations from a three-month period. For the pregnant women, hair samples for each trimester of pregnancy were analysed.

RESULTS

The mean hair cortisol concentration was 127.91 (111.52) pg/mg for the general sample. The variables of age, education, employment status, use of hair dyes, use of oral contraceptives, and physical exercise had a significant relation to HCC. When adjusted for further variables, only education and physical exercise remained statistically significant. When including the use of oral contraceptives and only with respect to females, only physical exercise remains statistically significant. For the subsample of pregnant woman, the mean hair cortisol concentration was 334.51 (409.77) pg/mg for the first trimester, 302.18 (270.24) pg/mg for the second trimester, and 331.31 (295.46) pg/mg for the third trimester of pregnancy. None of the assessed confounding variables (age, body mass index, previous miscarriages, employment status, hair dyes, dependent children and physical exercise), except education level, was related to HCC.

CONCLUSIONS

In this sample of healthy Spaniards, results suggested an association between HCC and physical exercise and educational level. In pregnant women, the prevalence of HCC was higher than in non-pregnant woman, and was related to educational level. This study emphasises the need to determine the relationship between HCC and confounders such as sociodemographic and lifestyle variables in the general population and specific groups formed by individuals such as pregnant women.

The effects of body region, season and external arsenic application on hair cortisol concentration

Hair cortisol analysis has been used to quantify hormone levels in circulation in several mammal species. Hair remains stable for decades or centuries, allowing researchers to use archived hair samples to investigate hormone levels that span long time periods. However, several studies have found that intra-individual variability, driven by the body region from which a sample is derived, confounds measurements of systemic glucocorticoid hormone concentrations. In addition, the external application of chemical agents to hair can remove or concentrate molecules of interest. These may preclude the use of samples that have been collected opportunistically and/or those that have been housed in museum collections. Using a captive population of Vancouver Island marmots (Marmota vancouverensis), we found a strong effect of body region on the concentration of cortisol within hair, as well as an effect of season. Using a collection of American mink (Neovison vison) pelts, we found that application of the preservative arsenic in the form of a soap does not cause a significant decrease in cortisol. The marmot results suggest that intra-individual variability is not stable through time. The reason for these seasonal effects is not clear and further study is necessary. Researchers using samples from an unknown body region should exercise caution in interpreting their results. The mink results suggest that samples held in museum collections can be used to quantify cortisol, even when arsenic preservation is suspected.

Ecological Context and Human Variation: Applying the Principles of Biological Anthropology to Psychoneuroimmunology

There is considerable research interest overlap between biological anthropology and psychoneuroimmunology (PNI), particularly given recent anthropological interest in endocrine and immune system functioning over the life span and in different environmental contexts. In this chapter, I argue that conducting research on non-WEIRD populations and applying an anthropological, evolutionary approach to PNI can greatly strengthen our understanding of immune-endocrine-behavior connections. This chapter reviews population-level variation in the human immune and endocrine systems, as well as genetic and environmental contributions to this variation. The effects of culture on shaping health outcomes and stress responses are also considered. Finally, this chapter discusses some noninvasive sampling methodologies appropriate to field research and alternatives to laboratory-based research designs. By confronting variable social and environmental contexts, PNI can greatly expand on its existing contributions to the treatment and understanding of depression, mood disorders, stress, and other aspects of health and well-being.

Testosterone-like immunoreactivity in hair measured in minute sample amounts - a competitive radioimmunoassay with an adequate limit of detection

The concentrations of testosterone deposited in hair during hair growth may provide a retrospective reflection of the concentrations of bioactive testosterone in plasma. The objective of this study was to develop a radioimmunoassay with a sufficiently low limit of detection to measure the testosterone-like immunoreactivity in smaller hair samples (5 mg) than used in earlier studies, and to compare three different extraction procedures. The competitive radioimmunoassay consisted of a polyclonal antiserum (immunogen testosterone-7α-BSA) and a radioligand synthesised from testosterone-3-CMO-histamine. The within-assay and total coefficients of variation in the working range was 3% and 4.5%, respectively. The limit of detection was 0.87 pg/mL, which is equivalent to 0.12 pg/mg testosterone in 5 mg of hair. The concentration of testosterone-like immunoreactivity in hair samples was 1.23 (SD 0.47) pg/mg in women and 2.67 (SD 0.58) pg/mg in men (pulverised hair). Significantly improved precision was found when pulverised hair was used compared to non-pulverised hair. Our data indicate that pulverisation of the hair prior to hormone extraction is crucial. Detection limits fit for the intended purpose are achievable with 5 mg samples of hair.

DHEAS patterning across childhood in three sub-Saharan populations: Associations with age, sex, ethnicity, and cortisol

OBJECTIVES

Hormones have many roles in human ontogeny, including the timing of life history 'switch points' across development. Limited hormonal data exist from non-Western children, leaving a significant gap in our understanding of the diversity of life history patterning. This cross-sectional study examines dehydroepiandrosterone sulfate (DHEAS) production in relation to age, sex, ethnicity, and cortisol concentrations, as well as average age of adrenarche, among Aka and Ngandu children of the Central African Republic and Sidama children of Ethiopia.

METHODS

Hair was collected from 480 children (160 per population) aged 3-18 years old. These samples were analyzed for DHEAS and cortisol concentrations using ELISAs. A generalized additive model was used to examine DHEAS patterning in relation to age, sex, cortisol, and ethnicity. The derivative of DHEAS as a function of age was used to identify average age of adrenarche in each population.

RESULTS

DHEAS patterning in these three populations is distinct from Euro-American patterns of production. In all three groups, the population-level age at adrenarche onset occurs slightly later than Euro-American averages, with both Central African populations experiencing a later onset than the Ethiopian population.

CONCLUSIONS

DHEAS patterns and age at adrenarche vary across cultures, perhaps indicating adaptive life history responses in diverse eco-cultural environments. Delayed involution of the fetal zone and DHEAS patterning may offer both cognitive protection and immune defense in high-risk, nutritionally-poor environments. Additional research in the majority world is essential to improving our understanding of the diversity of hormonal development and timing of 'switch points' in life history trajectories.

Multi-year longitudinal profiles of cortisol and corticosterone recovered from baleen of North Atlantic right whales (Eubalaena glacialis)

Research into stress physiology of mysticete whales has been hampered by difficulty in obtaining repeated physiological samples from individuals over time. We investigated whether multi-year longitudinal records of glucocorticoids can be reconstructed from serial sampling along full-length baleen plates (representing ∼10years of baleen growth), using baleen recovered from two female North Atlantic right whales (Eubalaena glacialis) of known reproductive history. Cortisol and corticosterone were quantified with immunoassay of subsamples taken every 4cm (representing ∼60d time intervals) along a full-length baleen plate from each female. In both whales, corticosterone was significantly elevated during known pregnancies (inferred from calf sightings and necropsy data) as compared to intercalving intervals; cortisol was significantly elevated during pregnancies in one female but not the other. Within intercalving intervals, corticosterone was significantly elevated during the first year (lactation year) and/or the second year (post-lactation year) as compared to later years of the intercalving interval, while cortisol showed more variable patterns. Cortisol occasionally showed brief high elevations ("spikes") not paralleled by corticosterone, suggesting that the two glucocorticoids might be differentially responsive to certain stressors. Generally, immunoreactive corticosterone was present in higher concentration in baleen than immunoreactive cortisol; corticosterone:cortisol ratio was usually >4 and was highly variable in both individuals. Further investigation of baleen cortisol and corticosterone profiles could prove fruitful for elucidating long-term, multi-year patterns in stress physiology of large whales, determined retrospectively from stranded or archived specimens.

The nexus of hair corticosterone level, immunocompetence, metabolic rates and overwinter survival in the root vole, Microtus oeconomus

Although corticosterone (CORT) regulates many physiological mechanisms, the associations between CORT levels, immunocompetence, energy expenditures and overwinter survival have not been examined. Here, we studied individual variation in CORT level extracted from hair, immunocompetence quantified as the neutrophil-to-lymphocyte (N/L) ratio, total white blood cells (WBC) and natural antibody levels (NAbs), along with the resting (RMR) and peak metabolic rates (PMR) and mortality during three consecutive winter seasons in a natural population of the root vole, Microtus oeconomus. In early winter, hair CORT level was strongly positively associated with body mass and inversely related to voles' ability to survive. We suggest that the observed association between hair CORT level and body mass may be the key component of the physiological nexus driving the survivorship of individual rodents. Additionally, hair CORT was a significant predictor of variation of the whole body RMR, which in turn enhanced overwinter survival in the studied population. On the other hand, hair CORT was not significantly associated with changes in the blood indices. Interestingly, the analysis carried out only during the first year of study (2008), which was characterized by a high population density and prevalence of infestation with a blood protozoan, Babesia spp., showed that the intensity of the infestation was negatively correlated with both the hair CORT level and the N/L ratio. Because CORT is often considered immunosuppressive, we expected a positive association between its level and the N/L ratio. However, hair CORT did not significantly correlate with the N/L ratio. We suggest that the lack of an association between hair CORT and the N/L ratio resulted from a small inter-individual variation in the N/L ratio in 2008, which was much higher and less variable than in the other years of our study.

Non-invasive monitoring of physiological markers in primates

The monitoring of endocrine markers that inform about an animal's physiological state has become an invaluable tool for studying the behavioral ecology of primates. While the collection of blood samples usually requires the animal to be caught and immobilized, non-invasively collected samples of saliva, urine, feces or hair can be obtained without any major disturbance of the subject of interest. Such samples enable repeated collection which is required for matching behavioral information over long time periods with detailed information on endocrine markers. We start our review by giving an overview of endocrine and immune markers that have been successfully monitored in relation to topics of interest in primate behavioral ecology. These topics include reproductive, nutritional and health status, changes during ontogeny, social behavior such as rank relationships, aggression and cooperation as well as welfare and conservation issues. We continue by explaining which hormones can be measured in which matrices, and potential problems with measurements. We then describe different methods of hormone measurements and address their advantages and disadvantages. We finally emphasize the importance of thorough validation procedures when measuring a specific hormone in a new species or matrix.

Individual-based analysis of hair corticosterone reveals factors influencing chronic stress in the American pika

Glucocorticoids are often measured in wildlife to assess physiological responses to environmental or ecological stress. Hair, blood, saliva, or fecal samples are generally used depending on the timescale of the stress response being investigated and species‐specific considerations. Here, we report the first use of hair samples to measure long‐term corticosterone levels in the climate‐sensitive American pika (Ochotona princeps). We validated an immunoassay‐based measurement of corticosterone extracted from hair samples and compared corticosterone estimates obtained from plasma, hair, and fecal samples of nine pikas. To demonstrate an ecological application of this technique, we characterized physiological stress in 49 pikas sampled and released at eight sites along two elevational transects. Microclimate variation was measured at each site using both ambient and subsurface temperature sensors. We used an information theoretic approach to compare support for linear, mixed‐effects models relating corticosterone estimates to microclimate, body size, and sex. Corticosterone was measured accurately in pika hair samples after correcting for the influence of sample mass on corticosterone extraction efficiency. Hair‐ and plasma‐based estimates of corticosterone were weakly correlated. The best‐supported model suggested that corticosterone was lower in larger, male pikas, and at locations with higher ambient temperatures in summer. Our results are consistent with a general negative relationship between body mass and glucocorticoid concentration observed across mammalian species, attributed to the higher mass‐specific metabolic rates of smaller bodied animals. The higher corticosterone levels in female pikas likely reflected the physiological demands of reproduction, as observed in a wide array of mammalian species. Additionally, we establish the first direct physiological evidence for thermal stress in the American pika through nonlethal sampling of corticosterone. Interestingly, our data suggest evidence for cold stress likely induced during the summer molting period. This technique should provide a useful tool to researchers wishing to assess chronic stress in climate‐sensitive mammals.

Hair cortisol and its potential value as a physiological measure of stress response in human and non-human animals

There is considerable interest in the potential for measuring cortisol in hair as a means of quantifying stress responses in human and non-human animals. This review updates the rapid advancement in our knowledge of hair cortisol, methods for its measurement, its relationship to acute and chronic stress, and its repeatability and heritability. The advantages of measuring cortisol in hair compared with other matrices such as blood, saliva and excreta and the current theories of the mechanisms of cortisol incorporation into the fibre are described. Hair cortisol as a measure of the physiological response to stress in a variety of species is presented, including correlations with other sample matrices, the relationship between hair cortisol and psychosocial stress and the repeatability and heritability of hair cortisol concentrations. Current standards for the quantification of hair cortisol are critically reviewed in detail for the first time and gaps in technical validation of these methods highlighted. The known effects of a variety of sources of hair cortisol variation are also reviewed, including hair sampling site, sex, age and adiposity. There is currently insufficient evidence to conclude that cortisol concentration in hair accurately reflects long-term blood cortisol concentrations. Similarly, there is a lack of information surrounding the mechanisms of cortisol incorporation into the hair. This review highlights several directions for future research to more fully validate the use of hair cortisol as an indicator of chronic stress.

Longitudinal progesterone profiles in baleen from female North Atlantic right whales (Eubalaena glacialis) match known calving history

Reproduction of mysticete whales is difficult to monitor, and basic parameters, such as pregnancy rate and inter-calving interval, remain unknown for many populations. We hypothesized that baleen plates (keratinous strips that grow downward from the palate of mysticete whales) might record previous pregnancies, in the form of high-progesterone regions in the sections of baleen that grew while the whale was pregnant. To test this hypothesis, longitudinal baleen progesterone profiles from two adult female North Atlantic right whales (Eubalaena glacialis) that died as a result of ship strike were compared with dates of known pregnancies inferred from calf sightings and post-mortem data. We sampled a full-length baleen plate from each female at 4 cm intervals from base (newest baleen) to tip (oldest baleen), each interval representing ∼60 days of baleen growth, with high-progesterone areas then sampled at 2 or 1 cm intervals. Pulverized baleen powder was assayed for progesterone using enzyme immunoassay. The date of growth of each sampling location on the baleen plate was estimated based on the distance from the base of the plate and baleen growth rates derived from annual cycles of stable isotope ratios. Baleen progesterone profiles from both whales showed dramatic elevations (two orders of magnitude higher than baseline) in areas corresponding to known pregnancies. Baleen hormone analysis shows great potential for estimation of recent reproductive history, inter-calving interval and general reproductive biology in this species and, possibly, in other mysticete whales.

Embryonic sex steroid hormones accumulate in the eggshell of loggerhead sea turtle (Caretta caretta)

Steroids hormones such as estradiol-17β (E2) and testosterone (T) are involved in gonadal differentiation of oviparous animals with temperature-dependent sex determination (TSD), and are greatly distributed. This hypothesizes that these embryonic steroid hormones probably accumulate in the eggshell throughout blood or/and chorioallantoic fluid in sea turtle species with TSD, producing females at higher temperature. To demonstrate this hypothesis, concentrations of E2 and T in the blood plasma from the hatchling loggerhead sea turtle (Caretta caretta) and in their eggshells were measured by radioimmunoassay. In the present study we propose that both concentrations of E2 and T in the blood plasma are correlated with amounts of these sex steroids in the eggshell. Moreover, contents of E2 in the eggshell showed a significant positive correlation with mean incubation temperatures during a thermosensitive period in the experimental nests, whereas T contents in the eggshell did not. Taken together, these findings indicated that embryonic E2 and T that accumulated in the eggshell can be extracted and measured. Furthermore, the present study suggested that contents of E2 in the eggshell may differ between male and female, and monitoring of these steroids is a useful method to identify the sex of loggerhead sea turtle hatchling.

The relationship between cortisol, stress and psychiatric illness: New insights using hair analysis

BACKGROUND

Stress is an established important contributor to the development of mental illness and stress related disorders. The biology implicated in the homeostasis of pathological stress mechanisms is not fully established. One of the difficulties with current techniques is the limitation in capturing chronic levels of cortisol as an expression of stress levels in humans. Hair samples can be used to evaluate cortisol levels averaged over relatively long periods of time, therefore providing a more valid measure of chronic levels of this hormone. A highly replicable technique to measure long-term cortisol could prove pivotal in improving our understanding of the role of stress in psychiatric disorders.

METHODS

This review synthesises all the published studies relating hair cortisol concentration (HCC) to stress and to psychiatric disorders. It describes and summarises their findings with the aim of providing a summary picture of the current state of this line of research.

RESULTS

The strongest finding to date is the replicable increases in hair cortisol associated with stressful life events. Findings in psychiatric disorders are more sparse and inconsistent. There is some support for the presence of raised HCC in major depressive disorders, and for lowered HCC in posttraumatic stress disorder, suggesting chronic hypercortisolaemia and hypocortisolaemia respectively.

CONCLUSIONS

HCC is a promising methodology to study chronic cortisol levels with the potential to help characterise psychiatric and stress related disorders. The combination of chronic and acute cortisol measurements has the potential for more accurately determining different aspects of the stress response, and ultimately for the development of a biological marker to aid diagnosis and response to treatment.

Associations between Parity, Hair Hormone Profiles during Pregnancy and Lactation, and Infant Development in Rhesus Monkeys (Macaca mulatta)

Studies examining hormones throughout pregnancy and lactation in women have been limited to single, or a few repeated, short-term measures of endocrine activity. Furthermore, potential differences in chronic hormonal changes across pregnancy/lactation between first-time and experienced mothers are not well understood, especially as they relate to infant development. Hormone concentrations in hair provide long-term assessments of hormone production, and studying these measures in non-human primates allows for repeated sampling under controlled conditions that are difficult to achieve in humans. We studied hormonal profiles in the hair of 26 female rhesus monkeys (Macaca mulatta, n=12 primiparous), to determine the influences of parity on chronic levels of cortisol (hair cortisol concentration, HCC) and progesterone (hair progesterone concentration, HPC) during early- to mid-pregnancy (PREG1), in late pregnancy/early lactation (PREG2/LACT1), and in peak lactation (LACT2). We also assessed infants' neurobehavioral development across the first month of life. After controlling for age and stage of pregnancy at the first hair sampling period, we found that HCCs overall peaked in PREG2/LACT1 (p=0.02), but only in primiparous monkeys (p<0.001). HPCs declined across pregnancy and lactation for all monkeys (p<0.01), and primiparous monkeys had higher HPCs overall than multiparous monkeys (p=0.02). Infants of primiparous mothers had lower sensorimotor reflex scores (p=0.02) and tended to be more irritable (p=0.05) and less consolable (p=0.08) in the first month of life. Moreover, across all subjects, HCCs in PREG2/LACT1 were positively correlated with irritability (r(s)=0.43, p=0.03) and negatively correlated with sensorimotor scores (r(s)=-0.41, p=0.04). Together, the present results indicate that primiparity influences both chronic maternal hormonal profiles and infant development. These effects may, in part, reflect differential reproductive and maternal effort in mothers with varied caretaking experience. In addition, infant exposure to relatively higher levels of maternal cortisol during the late fetal and early postnatal periods is predictive of poorer developmental outcomes.

Enzyme immunoassays as a method for quantifying hair reproductive hormones in two felid species

Non-invasive monitoring of wild felid reproductive states is important, given that many species reproduce poorly in captivity. Despite extensive work in faecal hormone analysis in felids, continued development of techniques is necessary, particularly with wild populations. In this study, our aims were as follows: (i) biochemical validation of enzyme immunoassays for estrogen, testosterone and progesterone in Canada lynx and domestic cat hair extracts; (ii) assessment of the use of hair reproductive hormones to differentiate between reproductive states (intact, estrus, pregnant and spayed/neutered), using domestic cats as a model; and (iii) assessment of the use of hair reproductive hormones to differentiate between age and sex, accounting for potential regional variability in wild lynx populations. Analysis of hair hormone levels showed prospective value in detecting pregnancy states, with pregnant domestic cats having higher levels of progesterone than spayed females. However, intact and pregnant cats did not differ in progesterone levels. Yet, two female domestic cats had higher levels of hair progesterone following a 38-day oral progestin treatment, perhaps providing a preliminary pharmacological validation of the method. Estrogen and testosterone did not differ statistically according to reproductive states of domestic cats, although intact males had higher levels of hair testosterone than neutered males. When we applied these techniques to lynx fur, we determined that hormone levels were not sufficiently precise to differentiate age classes. Hair reproductive hormone ratios differed between sexes, with the estrogen-to-progesterone ratio demonstrating the highest accuracy in differentiating males from females. Hair hormone levels differed regionally for wild lynx, indicating that spatial variability should be a consideration in wildlife hormone studies spanning large spatial scales. We conclude that use of hair hormone analysis by enzyme immunoassay may hold promise for differentiating sex in felids, but the technique will require further refinement and validation before it can be applied broadly and reliably.

The use of noninvasive and minimally invasive methods in endocrinology for threatened mammalian species conservation

Endocrinology is an indispensable tool in threatened species research. The study of endocrinology in threatened species not only advances knowledge of endocrine mechanism but also contributes to conservation efforts of studied species. To this end, endocrinology has been traditionally used to understand reproductive and adrenocortical endocrine axes by quantifying excreted steroid metabolites. From these studies a large body of knowledge was created that contributed to the field of endocrinology, aided conservation efforts, and created a template by which to validate and conduct this research for other species. In this regard noninvasive hormone monitoring has become a favored approach to study the basic endocrinology of wildlife species. Due to the increased understanding of endocrine physiology of threatened species, breeding rates of captive population have improved to levels allowing for reintroduction of species to restored natural ecosystems. Although these approaches are still employed, advances in biochemical, molecular, and genomic technologies are providing inroads to describe lesser known endocrine activity in threatened species. These new avenues of research will allow for growth of the field with greater depth and breadth. However, for all approaches to endocrinology, limitations on resources and access to animals will require innovation of current methodologies to permit broad application for use in threatened species research.

Hormones in infant rhesus monkeys' (Macaca mulatta) hair at birth provide a window into the fetal environment

BACKGROUND

It is established that maternal parity can affect infant growth and risk for several disorders, but the prenatal endocrine milieu that contributes to these outcomes is still largely unknown. Recently, it has been shown that hormones deposited in hair can provide a retrospective reflection of hormone levels while the hair was growing. Taking advantage of this finding, our study utilized hair at birth to investigate if maternal parity affected fetal hormone exposure during late gestation.

METHODS

Hair was collected from primiparous and multiparous mother and infant monkeys at birth and used to determine steroid hormones embedded in hair while the infant was in utero. A high-pressure liquid chromatography-triple quadrupole mass spectrometry technique was refined, which enabled the simultaneous measurement of eight hormones.

RESULTS

Hormone concentrations were dramatically higher in neonatal compared to maternal hair, reflecting extended fetal exposure as the first hair was growing. Further, hair cortisone was higher in primiparous mothers and infants when compared to the multiparous dyads.

CONCLUSION

This research demonstrates that infant hair can be used to track fetal hormone exposure and a panel of steroid hormones can be quantified from hair specimens. Given the utility in nonhuman primates, this approach can be translated to a clinical setting with human infants.

Analyses of fecal and hair glucocorticoids to evaluate short- and long-term stress and recovery of Asiatic black bears (Ursus thibetanus) removed from bile farms in China

Demand for traditional Chinese medicines has given rise to the practice of maintaining Asiatic black bears (Ursus thibetanus) in captivity to harvest bile. We evaluated hypothalamic-pituitary-adrenal (HPA) activity in Asiatic black bears on a bile farm in China by measuring cortisol in hair. We also monitored hair and fecal glucocorticoid metabolites as bears acclimated to improved husbandry at the Animals Asia Foundation China Bear Rescue Center (CBRC) after removal from other bile farms. Fecal samples were collected twice weekly for ~1 year, and hair was obtained from bears upon arrival at the CBRC and again ≥163 days later. Paired hair samples showed declines in cortisol concentrations of 12-88% in 38 of 45 (84%, p<0.001) bears after arrival and acclimation at the rehabilitation facility. Concentrations of cortisol in hair from bears on the bile farm were similar to initial concentrations upon arrival at the CBRC but were higher than those collected after bears had been at the CBRC for ≥163 days. Fecal glucocorticoid concentrations varied across months and were highest in April and declined through December, possibly reflecting seasonal patterns, responses to the arrival and socialization of new bears at the CBRC, and/or annual metabolic change. Data from segmental analysis of hair supports the first of these explanations. Our findings indicate that bears produced elevated concentrations of glucocorticoids on bile farms, and that activity of the HPA axis declined following relocation. Thus, hair cortisol analyses are particularly well suited to long-term, retrospective assessments of glucocorticoids in ursids. By contrast, fecal measures were not clearly associated with rehabilitation, but rather reflected more subtle endocrine changes, possibly related to seasonality.

Analysis of cortisol in hair--state of the art and future directions

Changes to long-term secretion of the glucocorticoid cortisol are considered to play a crucial role in mediating the link between chronic stress and the development of numerous immune system related diseases. However, obtaining valid assessments of long-term cortisol levels is difficult due to limitations of previous measurement strategies in blood, saliva or urine. This review discusses evidence on a recent methodological development assumed to provide a considerable advancement in this respect: the analysis of cortisol in hair. Being incorporated into the growing hair, hair cortisol concentrations (HCC) are assumed to provide a retrospective reflection of integrated cortisol secretion over periods of several months. Over the past years, supportive evidence has accumulated regarding several fundamental characteristics of HCC, including its validity as an index of long-term systemic cortisol levels, its reliability across repeated assessments and its relative robustness to a range of potential confounding influences. Based on this groundwork, research has now also commenced to utilise HCC for answering more specific questions regarding the role of long-term cortisol secretion in different stress and health-related conditions. The possibility of extending hair analysis to also capture long-term secretion of other steroid hormones (e.g., androgens or estrogens) provides a further intriguing prospect for future research. Given its unique characteristics, the use of hair analysis holds great promise to significantly enhance current understanding on the role of steroid hormones in psychoimmunological research.

Cortisol levels in hair reflect behavioural reactivity of dogs to acoustic stimuli

Cortisol levels in hair samples were examined in fourteen domestic dogs and related to the dogs' responses to different acoustic stimuli. Stimuli were playbacks of species-typical vocalizations recorded during three different situations ("disturbance", "isolation" and "play" barks) and the sounds of a thunderstorm. Hair samples were collected at 9:00 h and 17:00 h two weeks after the behavioural tests. Results showed that behavioural reactivity to playback of the various stimuli correlates with cortisol levels in hair samples collected at 9:00 h, and the same was the case for the separate measures of behaviour (i.e. hiding, running away, seeking attention from the tester, panting and lowering of the body posture). Hence, levels of cortisol in hair appear to reflect the dog's chronic state of emotional reactivity, or temperament.

Stress-linked cortisol concentrations in hair: what we know and what we need to know

Cortisol has major impacts upon a range of physiological homeostatic mechanisms and plays an important role in stress, anxiety and depression. Although traditionally described as being solely synthesised via the hypothalamic-pituitary-adrenal (HPA) axis, recent animal and human studies indicate that cortisol may also be synthesised via a functionally-equivalent 'peripheral' HPA-like process within the skin, principally within hair follicles, melanocytes, epidermal melanocytes and dermal fibroblasts. Current data indicate that basal levels of cortisol within hair vary across body regions, show diurnal variation effects, respond to the onset and cessation of environmental stressors, and may demonstrate some degree of localisation in those responses. There are conflicting data regarding the presence of variability in cortisol concentrations across the length of the hair shaft, thus challenging the suggestion that hair cortisol may be used as a historical biomarker of stress and questioning the primary origin of cortisol in hair. The need to comprehensively 'map' the hair cortisol response for age, gender, diurnal rhythm and responsivity to stressor type is discussed, plus the major issue of if, and how, the peripheral and central HPA systems communicate.

Hair cortisol levels track phylogenetic and age related differences in hypothalamic-pituitary-adrenal (HPA) axis activity in non-human primates

Hair has been shown to archive a uniquely time averaged signal of endocrine activity, and holds attractive advantages for both laboratory and field research. Prior research has explored the potential of hair hormone analysis to examine hormone-behavior relationships. To date, no research has focused on the potential of the technique to investigate age-related changes or taxon differences in endocrine function. It is known that non-human primate infants of many taxa exhibit high cortisol levels after parturition, which rapidly decline with age. It has also been shown that hypercortisolism generally characterizes platyrrhine (New World monkey) endocrine function. These endocrine trends have been characterized using cortisol levels determined from serum, plasma, and feces. Here we test whether cortisol levels determined from hair recover similar phylogenetic and age related patterns in endocrine function in non-human primates. In order to test whether hair cortisol reflect infant hypercortisolism with significant age-related decline, hair cortisol levels are measured in samples from wild vervet monkeys (Chlorocebus aethiops) and captive Guinea baboons (Papio hamadryas papio), ranging in age from infants through juveniles. Further, in order to test whether platyrrhines exhibit significantly higher hair cortisol levels compared to strepsirrhines and catarrhines, and therefore faithfully recover similar signals as more traditionally used substrates (e.g. serum), hair cortisol levels are quantified in adult female hair samples collected from a broad range of non-human primate taxa. Results confirm that hair cortisol levels accurately reflect known phylogenetic and age related patterns of circulating cortisol levels. Therefore, these results suggest that hair may be an ideal hormone bearing substrate for research focused on the examination of population endocrine profiles, cross-sectional studies of endocrine function and taxon variation in hormone levels, as well as stable behavioral trends.

Cortisol in hair measured in young adults - a biomarker of major life stressors?

Background

Stress as a cause of illness has been firmly established. In public health and stress research a retrospective biomarker of extended stress would be an indispensible aid. The objective of this pilot study was to investigate whether concentrations of cortisol in hair correlate with perceived stress, experiences of serious life events, and perceived health in young adults.

Methods

Hair samples were cut from the posterior vertex area of (n = 99) university students who also answered a questionnaire covering experiences of serious life events, perceived Stress Scale and perceived health during the last three months. Cortisol was measured using a competitive radioimmunoassay in methanol extracts of hair samples frozen in liquid nitrogen and mechanically pulverised.

Results

Mean cortisol levels were significantly related to serious life events (p = 0.045), weakly negatively correlated to perceived stress (p = 0.025, r = -0.061) but nor affected by sex, coloured/permed hair, intake of pharmaceuticals or self-reported health. In a multiple regression model, only the indicator of serious life events had an independent (p = 0.041) explanation of increased levels of cortisol in hair. Out of four outliers with extremely high cortisol levels two could be contacted, both reported serious psychological problems.

Conclusions

These findings suggest that measurement of cortisol in hair could serve as a retrospective biomarker of increased cortisol production reflecting exposure to major life stressors and possibly extended psychological illness with important implications for research, clinical practice and public health. Experience of serious life events seems to be more important in raising cortisol levels in hair than perceived stress.

Evaluation of a method to measure long term cortisol levels

INTRODUCTION

Elevated levels of cortisol are known to induce various symptoms and diseases, e.g. abdominal obesity, type 2 diabetes, osteoporosis and cardiovascular disease. Measuring serum, saliva and urine cortisol is limited to one time point. Measurement of cortisol in scalp hair is a recently developed method to measure long term cortisol levels. The aim of this study was to investigate whether hair cortisol is a feasible parameter to measure cortisol exposure.

EXPERIMENTAL

We collected hair samples of 195 healthy individuals, 9 hypercortisolemic and one hypocortisolemic patient and measured hair cortisol levels. Cortisol was extracted from scalp hair using methanol and cortisol levels were measured using a salivary ELISA kit. Measurement of waist and hip circumferences and blood pressure was performed in 46 healthy subjects.

RESULTS

We found a positive correlation between hair cortisol and both waist circumference (r=0.392, p=0.007) and waist-to-hip ratio (WHR) (r=0.425, p=0.003). No correlations were found between hair cortisol levels and BMI, blood pressure or age. There was no decline in cortisol levels in six consecutive hair segments. Hair cortisol levels were elevated in patients with known hypercortisolism (p<0.0001).

CONCLUSIONS

Hair cortisol was positively correlated with WHR, suggesting that hair cortisol reflects cortisol exposure at tissue level, which was also supported by elevated hair cortisol levels in hypercortisolemic patients and concordance between hair cortisol levels and clinical disease course. Cortisol levels in hair are slightly influenced by hair treatment but not by natural hair colour, use of hair products, gender or age.

An Investigation of Hair Cortisol Concentration Across Body Sites and within Hair Shaft

Cortisol concentrations in hair collected from young male and female adults were assayed and compared for differences along shaft length and between body sites. No significant differences were found between hair shaft sites, supporting a model of the hair shaft as "alive" and responsive to environmental demand in terms of cortisol production. Hair taken from forearms had significantly higher concentrations of cortisol than hair from lower legs, suggesting a localized hair cortisol response and verifying previous findings. Issues of the link between central and peripheral HPA axes are raised for discussion and further investigation.

Hair analysis provides a historical record of cortisol levels in Cushing's syndrome

The severity of Cushing's Syndrome (CS) depends on the duration and extent of the exposure to excess glucocorticoids. Current measurements of cortisol in serum, saliva and urine reflect systemic cortisol levels at the time of sample collection, but cannot assess past cortisol levels. Hair cortisol levels may be increased in patients with CS, and, as hair grows about 1 cm/month, measurement of hair cortisol may provide historical information on the development of hypercortisolism. We attempted to measure cortisol in hair in relation to clinical course in six female patients with CS and in 32 healthy volunteers in 1 cm hair sections. Hair cortisol content was measured using a commercially available salivary cortisol immune assay with a protocol modified for use with hair. Hair cortisol levels were higher in patients with CS than in controls, the medians (ranges) were 679 (279-2500) and 116 (26-204) ng/g respectively (P<0.001). Segmental hair analysis provided information for up to 18 months before time of sampling. Hair cortisol concentrations appeared to vary in accordance with the clinical course. Based on these data, we suggest that hair cortisol measurement is a novel method for assessing dynamic systemic cortisol exposure and provides unique historical information on variation in cortisol, and that more research is required to fully understand the utility and limits of this technique.

An assessment of cortisol analysis in hair and its clinical applications

Hair analyses for exogenous compounds, specifically drugs of abuse, have been a useful tool in detecting long-term drug exposure. More recently, studies have delved into the exposure of endogenous compounds in hair. Cortisol is synthesized in the adrenal cortex in response to stress-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis. While catecholamines generally indicate acute stress, cortisol can be used as an indicator for sub-acute and chronic stress. Studies on the effects of chronic stress are most often subjective in nature, relying on questionnaires asking the participant to recall on past stressors. This can lead to the issue of recall and reporting bias. A new objective measure of chronic stress is needed for a more accurate understanding of the effects of chronic stress on the body. This review uses emerging evidence to describe the usefulness of hair analysis for cortisol and discusses the current methods used.

Elevated content of cortisol in hair of patients with severe chronic pain: a novel biomarker for stress

Hair analysis has been used to reflect long-term systemic exposure to exogenous drugs and toxins. Several studies have demonstrated the feasibility of measuring endogenous steroid hormones, e.g. cortisol, in hair. Recently, a study in macaques showed a significant increase in hair cortisol levels induced by stress. We explored whether hair cortisol levels may be used as a biomarker for long-term stress in humans. Patients with severe chronic pain, aged 18 years or older, receiving opioid treatment for at least one year were recruited. Controls were non-obese (body mass index, BMI < 30 mg/kg(2)) adults. The Perceived Stress Scale (PSS) questionnaire was used to assess perceived stress over the last 4 weeks. A hair sample was obtained from the vertex posterior. Cortisol was measured using an enzyme-linked immunosorbent assay. We included fifteen patients (nine females and six males) and 39 non-obese control subjects (20 females, 19 males). PSS scores (median and range) were significantly higher in chronic pain patients (24: 12-28) than in controls (12: 3-31)(P < 0.001). Hair cortisol contents (median and range) were significantly greater in chronic pain patients (83.1: 33.0-205 g/mg) than in controls (46.1: 27.2-200 pg/mg) (P < 0.01). We conclude that hair cortisol contents are increased in patients with major chronic stress. Measurement of cortisol levels in hair constitutes a novel biomarker of prolonged stress.

Social status and cortisol levels in singing rock hyraxes

Many mammals use acoustic signals to communicate with conspecifics. Rock hyraxes (Procavia capensis) are social mammals whose vocal communication is usually restricted to quiet sounds used between nearby individuals. Loud repetitive warning trills are an exception. In our study site, a third of the adult male hyraxes also produces a rich, complex and loud vocalization we term 'singing'. In this study, we examine whether singers, which are more conspicuous by the act of singing, have higher cortisol (i.e. basal stress; C) levels than non-singers, and whether there is an association between social status and stress hormones in male hyraxes. We show that 'singing' males are different from the general adult male population in that their C levels are higher than those of silent males. Only in singers, C levels are associated with social rank, with dominants showing the highest levels. Singers are also on average older and more dominant than most other sexually mature non-singing males. Further, they copulate more than non-singers, suggesting that singing males may have higher reproductive success. Our results support the 'stress of domination' hypothesis and indicate that in the rock hyrax singing may reflect high competitive ability, designating singers as a distinct class of males, unique in their personal attributes and behavior.