Integrating cortisol and isotopic analyses of archeological hair: Reconstructing individual experiences of health and stress

Diets, stress, and disease in the Etruscan society: Isotope analysis and infantile skeletal palaeopathology from Pontecagnano (Campania, southern Italy, 730-580 BCE)

Susceptibility to morbidity and mortality is increased in early life, yet proactive measures, such as breastfeeding and weaning practices, can be taken through specific investments from parents and wider society. The extent to which such biosocialcultural investment was achieved within 1st millennium BCE Etruscan society, of whom little written sources are available, is unkown. This research investigates life histories in non-adults and adults from Pontecagnano (southern Italy, 730-580 BCE) in order to track cross-sectional and longitudinal breastfeeding and weaning patterns and to characterize the diet more broadly. Stable carbon and nitrogen isotope analysis of incrementally-sampled deciduous and permanent dentine (n = 15), bulk bone collagen (n = 38), and tooth enamel bioapatite (n = 21) reveal the diet was largely based on C3 staple crops with marginal contributions of animal protein. Millet was found to play a role for maternal diet and trajectories of breastfeeding and feeding for some infants and children at the site. The combination of multiple isotope systems and tissues demonstrates exclusive breastfeeding was pursued until 0.6 years, followed by progressive introduction of proteanocius supplementary foods during weaning that lasted between approximately 0.7 and 2.6 years. The combination of biochemical data with macroscopic skeletal lesions of infantile metabolic diseases and physiological stress markers showed high δ15Ndentine in the months prior to death consistent with the isotopic pattern of opposing covariance.

South American Archaeological Isotopic Database, a regional-scale multi-isotope data compendium for research

The South American Archaeological Isotopic Database (SAAID) is a comprehensive open-access resource that aggregates all available bioarchaeological stable and radiogenic isotope measurements, encompassing data from human individuals, animals, and plants across South America. Resulting from a collaborative effort of scholars who work with stable isotopes in this region, SAAID contains 53,781 isotopic measurements across 24,507 entries from individuals/specimens spanning over 12,000 years. SAAID includes valuable contextual information on archaeological samples and respective sites, such as chronology, geographical region, biome, and spatial coordinates, biological details like estimated sex and age for human individuals, and taxonomic description for fauna and flora. SAAID is hosted at the PACHAMAMA community within the Pandora data platform and the CORA repository to facilitate easy access. Because of its rich data structure, SAAID is particularly well-suited for conducting spatiotemporal meta-analyses. It serves as a valuable tool for addressing a variety of research topics, including the spread, adoption, and consumption intensification of food items, paleo-environmental reconstruction, as well as the exploration of mobility patterns across extensive geographic regions.

Hair glucocorticoids are not a historical marker of stress - Exploring the time-scale of corticosterone incorporation into hairs in a rat model

Hair glucocorticoids are increasingly popular biomarkers, used across numerous research fields, and studied species, as a measure of stress. Although they are suggested to be a proxy of the average HPA axis activity spanning a period of weeks or months into the past, this theory has never been tested. In the present study, adrenalectomized rats with no endogenous (adrenal) glucocorticoid production were used to study how circulating glucocorticoid levels would be reflected in the glucocorticoid levels found in hair samples. By dosing the animals daily with high levels of corticosterone for seven days, while sampling hairs before, during, and after treatments, a timeline for glucocorticoid uptake into hairs was constructed. This kinetic profile was compared to two hypothetical models, and the theory that hair glucocorticoids are a record of historical stress had to be rejected. Corticosterone concentrations in hairs were found to increase within three hours of the first injection, the highest concentrations were found on the seventh day of treatments, and the decrease in concentrations post-treatment suggests rapid elimination. We speculate that hair glucocorticoid levels can only be used to characterize a stress-response for a few days following a postulated stressor. An updated model, where glucocorticoids diffuse into, along, and out of hairs needs to be adopted to reconcile the experimentally obtained data. The inescapable consequence of this updated model is that hair glucocorticoids become a marker of - and can only be used to study - recent, or ongoing, stress, as opposed to historical events, weeks or months in the past.

Testosterone histories from tusks reveal woolly mammoth musth episodes

Hormones in biological media reveal endocrine activity related to development, reproduction, disease and stress on different timescales¹. Serum provides immediate circulating concentrations², whereas various tissues record steroid hormones accumulated over time^3,4. Hormones have been studied in keratin, bones and teeth in modern^5-8 and ancient contexts^9-12; however, the biological significance of such records is subject to ongoing debate^10,13-16, and the utility of tooth-associated hormones has not previously been demonstrated. Here we use liquid chromatography with tandem mass spectrometry paired with fine-scale serial sampling to measure steroid hormone concentrations in modern and fossil tusk dentin. An adult male African elephant (Loxodonta africana) tusk shows periodic increases in testosterone that reveal episodes of musth^17-19, an annually recurring period of behavioural and physiological changes that enhance mating success^20-23. Parallel assessments of a male woolly mammoth (Mammuthus primigenius) tusk show that mammoths also experienced musth. These results set the stage for wide-ranging studies using steroids preserved in dentin to investigate development, reproduction and stress in modern and extinct mammals. Because dentin grows by apposition, resists degradation, and often contains growth lines, teeth have advantages over other tissues that are used as records of endocrine data. Given the low mass of dentin powder required for analytical precision, we anticipate dentin-hormone studies to extend to smaller animals. Thus, in addition to broad applications in zoology and palaeontology, tooth hormone records could support medical, forensic, veterinary and archaeological studies.

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.

Reproductive life histories: can incremental dentine isotope analysis identify pubertal growth, pregnancy and lactation?

BACKGROUND

There are few reliable osteological indicators to detect parity or infer puberty in skeletal remains. Nitrogen (δ¹⁵N) and stable carbon (δ¹³C) isotope ratios in human tissues can be affected by metabolically unbalanced states engendered by pregnancy or rapid growth, offering potential biomarkers.

AIM

This pilot study explores the potential of incremental dentine-collagen isotope ratio analysis to identify puberty and gestation.

SUBJECTS AND METHODS

Incremental dentine δ¹⁵N and δ¹³C profiles were produced by analysing third molars extracted as part of dental treatment of 10 individuals living in Sudan. Demographic and anthropometric data at the time of tooth extraction was available. Medical histories were unknown.

RESULTS

Isotopic signatures potentially related to pubertal growth, with an average δ¹⁵N reduction of 0.78 ± 0.29‰, are indicated. Six isotopic signals suggestive of pregnancy, with an average δ¹⁵N decrease of 0.48 ± 0.22‰, are also observed. The timing, speed and amplitude of post-partum δ¹⁵N patterns seemingly infer infant feeding practices and maternal nutritional status.

CONCLUSION

This pilot study highlights the potential of incremental dentine isotope analysis for the reconstruction of early reproductive histories in skeletal remains. However, controlled studies with a larger human cohort are needed to validate these findings, establish isotopic signals linked to puberty and lactation, and improve chronology accuracy.

Analysis of hair steroid hormones in polar bears (Ursus maritimus) via liquid chromatography-tandem mass spectrometry: comparison with two immunoassays and application for longitudinal monitoring in zoos

Analysis of hair cortisol concentrations (HCCs) is a promising method for monitoring long-term stress in mammals. However, previous measurements of HCCs in polar bears (Ursus maritimus) have yielded highly variable results, which are likely due to different methodological approaches. In this study, hair samples of zoo-housed polar bears were analyzed for cortisol with two independent immunoassays [an enzyme-linked immunoassay (EIA) and a chemiluminescence assay (CLIA)] and liquid chromatography-tandem mass spectrometry (LC-MS/MS). HCC measurements depended significantly on assay type applied, sample processing (cutting vs. powdering hair) and their interaction. Best agreement was observed between LC-MS/MS and CLIA (R² = 0.81 for powdered hair) and sample processing had a minor, albeit significant, effect on obtained HCC measurements in these assays (R² > 0.9). EIA measurements were consistently higher than with the other assays. HCC measurement was validated biologically for CLIA and LC-MS/MS in one male polar bear that experienced considerable stress for a prolonged period of time (> 18 weeks). Subsequently, by using the validated LC-MS/MS the measurement of cortisol could be complemented by the analysis of other steroids including cortisone, testosterone and progesterone levels from hair samples collected over a 9-month period (5-13 months) from six zoo-housed polar bears (five males, one female). No seasonal steroid variation was observed except in male progesterone levels. For all steroids except cortisone, a strong body region effect (neck or paw) was observed. Cortisol and cortisone, as well as progesterone and testosterone, concentrations were positively correlated. We show that hair steroid concentrations can be used to longitudinally measure stress and reproductive hormone axes in polar bears. The data established herein provide important basic information regarding methodology and study design for assessing hair steroid hormones.

The "weanling's dilemma" revisited: Evolving bodies of evidence and the problem of infant paleodietary interpretation

Breastfeeding is known to be a powerful mediator of maternal and childhood health, with impacts throughout the life course. Paleodietary studies of the past 30 years have accordingly taken an enduring interest in the health and diet of young children as a potential indicator of population fertility, subsistence, and mortality patterns. While progress has been made in recent decades toward acknowledging the agency of children, many paleodietary reconstructions have failed to incorporate developments in cognate disciplines revealing synergistic dynamics between maternal and offspring biology. Paleodietary interpretation has relied heavily on the "weanling's dilemma," in which infants are thought to face a bleak choice between loss of immunity or malnutrition. Using a review of immunological and epidemiological evidence for the dynamic and supportive role that breastfeeding plays throughout the complementary feeding period, this article offers context and nuance for understanding past feeding transitions. We suggest that future interpretative frameworks for infant paleodietary and bioarchaeological research should include a broad knowledge base that keeps pace with relevant developments outside of those disciplines.

Desperately seeking stress: A pilot study of cortisol in archaeological tooth structures

OBJECTIVES

Cortisol is a glucocorticoid hormone produced through activation of the hypothalamic pituitary adrenal axis. It is known as the "stress hormone" for its primary role in the body's stress response and has been the focus of much modern clinical research. Within archaeology, only a few studies have analyzed cortisol in human remains and these have been restricted to hair (Webb et al., 2010; Webb, White, van Uum, & Longstaffe, 2015a; Webb, White, van Uum, & Longstaffe, 2015b). This study examines the utility of dentine and enamel, which survive well archaeologically, as possible reservoirs for detectable levels of cortisol.

MATERIALS AND METHODS

Then, 69 teeth from 65 individuals from five Roman and Post-Roman sites in France were tested via competitive enzyme-linked immunosorbent assay (ELISA) to assess and quantify the cortisol concentrations present within tooth dentine and enamel.

RESULTS

In both tooth dentine and enamel, detectable concentrations of cortisol were identified in multiple teeth. However, concentrations were low and not all teeth yielded results that were measurable through cortisol ELISA. Differences in cortisol values between dentine and enamel could suggest different uptake mechanisms or timing.

DISCUSSION

These results suggest that cortisol is incorporated within tooth structures and merits further investigation in both modern and archaeological contexts. Analysis of the results through liquid chromatographic-mass spectrometry would verify current results and might yield values that could be better integrated with published cortisol studies. Future studies of cortisol in tooth structures would greatly expand the research potential of cortisol in the past and could have implications for studies of human stress across deep time.

Advances in regional paleopathology of the Southern Coast of the Central Andes

Because of a rich cultural history and excellent preservation of archaeological materials the south coast of the Central Andes is a region where many anthropological questions can be explored, using the latest methods and techniques. Over the last 20 years, multidisciplinary paleopathological studies have revealed interesting and unanticipated perspectives regarding the lives and cultures of the peoples who inhabited this region in pre-Hispanic times. This paper presents a panorama of these recent investigations, beginning with a review of the data sources - the collections of human remains - available for study, their numbers, preservation, accessibility, strengths and weaknesses. Then follows a revision of recent investigations, presenting new knowledge about temporal trends in human health in the region, including mortality curves, stature achieved in adulthood, porotic hyperososis, cribra orbitalia, linear enamel hypoplasias, dental caries, biochemical analysis, trauma, and violence. This review shows how the knowledge of the history of this region has increased but also the many new questions that have emerged. Hopefully this paper will encourage more investigation, as the collections of human remains from this region are abundant, well documented and well preserved.

A multi-isotope, multi-tissue study of colonial origins and diet in New Zealand

OBJECTIVES

Colonial period New Zealand was lauded as a land of plenty, where colonists could improve their station in life and secure a future for their families. Our understanding of colonial experience, however, is often shaped by historical records which communicate a state-sponsored version of history. This study aims to reconstruct the lives of settlers using isotopic evidence from the colonial skeletons themselves.

MATERIALS AND METHODS

We use skeletal remains from recently excavated colonial sites in Otago (South Island, New Zealand) to illustrate the information that can be gleaned from the isotopic analysis of individuals. We use ⁸⁷ Sr/⁸⁶ Sr to identify European settlers, and δ¹³ C and δ¹⁵ N from collagen and hair keratin, as well as dental enamel carbonate δ¹³ C to trace dietary change over their life-courses.

RESULTS

Strontium isotope analysis shows that all adults in our sample are non-local. Dietary isotopes show that while most individuals had relatively consistent childhood diet, one individual with more rural origins likely had seasonal use of resources during childhood. While some members of the population seem to have increased their meat intake in the new colony most do not have clear evidence for this.

DISCUSSION

We show the diversity of human experience in first-generation New Zealanders both prior to emigration and in the new colony. Despite colonial propaganda claiming that circumstances in New Zealand were improved for all settlers, we have little evidence for this, aside from among individuals of potentially high status.

The Nitrogen Isotope Ratio Is a Biomarker of Yup'ik Traditional Food Intake and Reflects Dietary Seasonality in Segmental Hair Analyses

BACKGROUND

The nitrogen isotope ratio (NIR) is a promising index of traditional food intake for an Alaska Native (Yup'ik) population, which can be measured in blood and hair. However, the NIR has not been calibrated to high-quality measures of Yup'ik traditional food intake.

OBJECTIVES

Our primary objective was to examine associations between intakes of Yup'ik traditional food groups, including fish, marine mammals, birds, land mammals, berries, greens, and total traditional foods, and the NIR. In an exploratory analysis, we also examined whether NIR analyzed sequentially along hair could reflect dietary seasonality.

METHODS

We recruited 68 participants from 2 Yup'ik communities in the Yukon Kuskokwim region of Southwest Alaska (49% female, aged 14-79 y). Participants completed 4 unscheduled 24-h food recalls over the period peak of RBC and hair synthesis preceding a specimen collection visit. The NIR was measured in RBCs ( n = 68), a proximal hair section (n = 58), and sequential segments of hair from individuals in the upper 2 quartiles of traditional food intake having hair >6 cm in length, plus 2 low subsistence participants for reference (n = 18). Diet-biomarker associations were assessed using Pearson's correlation and linear regression.

RESULTS

Intakes of fish, marine mammals, berries, and greens were significantly associated with the NIR. The strongest dietary association was with total traditional food intake (R2 = 0.62), which indicated that each 1‰ increase in the RBC NIR corresponded to 8% of energy from traditional foods. Hair NIR appeared to fluctuate seasonally in some individuals, peaking in the summertime.

CONCLUSIONS

Findings support the use of the RBC and hair NIR to assess total traditional food intake in a Yup'ik population. Analyses of sequential hair NIR provided evidence of seasonality in traditional food intake, although seasonal variations were modest relative to interindividual variation.

Analysis of 19 Minerals and Cortisol in Red Deer Hair in Two Different Areas of the Stelvio National Park: A Preliminary Study

Simple Summary

Minerals play an important role in animals’ health and nutritional status and are associated with cortisol, a hormone involved in several physiological processes and with a fundamental role in allostasis, the process of achieving homeostasis. The aim of the present study is to perform a preliminary investigation on the concentration of 19 minerals and cortisol in the hair of red deer coming from two different areas of the Stelvio National Park. Results showed a close association between hair minerals and cortisol concentrations and an effect of deer origin. Hair minerals and cortisol assessment is an easy, rapid, and low cost screening method and it is useful in wildlife management programs, in order to investigate wild animals’ health status, to perform environmental studies, to assess the presence of contaminants in wild species and to determine risks for humans. In addition, it could be helpful in public health programs to estimate contamination risks linked to wild animal meat consumption or to assess the presence of contaminants in food-producing animals.

Abstract

The aim of the study was to perform an investigation on the concentration of 19 minerals and cortisol in red deer (Cervus elaphus) hair, a matrix that is easy to collect with non-invasive and painless sampling, able to represent an integrative values of long-term substance concentrations, and able to give useful information, also when performed on dead animals, given its extreme stability over time. In the study thirty-five animals were included, coming from two different sides of a valley in the Stelvio National Park, where official water analysis had pointed out elevated concentrations of As in one of the two orographic sides. Hair cortisol concentrations were measured using a RIA(Radio Immuno Assay), while minerals were detected using ICP-MS (Inductively Coupled Plasma- Mass Spectrometry). Results showed a negative relationship between cortisol and some mineral concentrations (Li, Co, As, Cd, Cr and Tl) and significant differences in some mineral concentrations between park areas (Al, Co, Cu, Cd and Ni). As, Cr and cortisol differences approached statistical significance. This preliminary study represents a step forward in the study of wildlife allostatic load and a valid method for applications in wildlife management programs, in environmental studies and in public health programs.

A 'cold case' of care: Looking at old data from a new perspective in mummy research

In 1973, analysis of the mummified remains of a young boy dated to 700AD and from the Late Nasca period (Peru) identified (i) chronic Pott's disease, leading to loss of lower body mobility, and (ii) acute miliary tuberculosis, affecting most organs and the immediate cause of death (Allison et al., 1973). This report was the first to establish, beyond dispute, the presence of tuberculosis in the Americas before the arrival of Europeans. Here, we revisit the 'Nasca Boy' from a bioarchaeology of care perspective. Contextualising the original study's results within what is known of contemporary lifeways, we apply the bioarchaeology of care methodology in considering the Nasca Boy's experience of living with tuberculosis; the type of care he required and how this may have evolved over a period of deteriorating health; and what such caregiving may suggest both about social organisation within his community and some of the more everyday aspects of Nasca existence. Up to now, the bioarchaeology of care approach has been employed almost exclusively with skeletal evidence; in this analysis of the Nasca Boy's remains, and in the accompanying wider-ranging discussion, we illustrate the potential of preserved soft tissue evidence to contribute to research into disability and care in the past. Although this report functions as a stand-alone case study, to obtain maximum benefit it should be read in conjunction with the Introduction to the special International Journal of Paleopathology issue on 'mummy studies and the bioarchaeology of care' (Nystrom and Tilley, 2018).

Hair cortisol and stable carbon and nitrogen isotope ratios in barbary macaques (Macaca sylvanus) from Gibraltar

RATIONALE

Prolonged exposure to the stress hormone cortisol can precipitate a catabolic state in animals resulting in a negative nitrogen balance and increased excreted nitrogen, possibly affecting stable nitrogen and carbon isotope ratios in animal tissues. Here we test the hypothesis that stress, as measured by hair cortisol, is a significant contributor to variation in δ¹⁵ N and δ¹³ C values in hair. The results of the present study have important implications for the use of stable carbon and nitrogen isotope ratios measured in animal and human tissues to make inferences regarding feeding ecology and diet.

METHODS

Samples containing roughly 10-20 hairs (approx. 4-6 cm long) were collected from 49 free ranging macaque monkeys (Macaca sylvanus) in Gibraltar. Hair samples were analyzed for stable carbon and nitrogen isotopes by continuous-flow isotope-ratio mass spectrometry. Cortisol extracted from matched hair samples was measured using gas chromatography/mass spectrometry. Cortisol and stable isotope ratios were compared statistically using nonparametric Kruskal-Wallis and Mann-Whitney U tests, as well as Spearman correlation.

RESULTS

Correlation analysis revealed that although hair δ¹⁵ N and δ¹³ C values were significantly correlated with each other, neither was correlated with cortisol concentrations. Cortisol concentrations were not correlated with age-adjusted body mass index. Age category was correlated with δ¹³ C values but not with δ¹⁵ N values.

CONCLUSIONS

The results of our study suggest that the cumulative stress experienced by these macaques under typical social and environmental conditions is not a significant contributor to variation in δ¹⁵ N and δ¹³ C values, nor does it have a significant effect on relative body mass.

Hair cortisol analysis: An update on methodological considerations and clinical applications

BACKGROUND

Hair cortisol analysis is increasingly being appreciated and applied in both research and medicine, aiding endocrinologists with diagnosis.

CONTENT

We provide an overview of hair cortisol research in general and an update on methodological considerations including the incorporation of cortisol into hair, hair growth rates, and sampling procedures, mincing vs. grinding of samples during preparation for extraction, various extraction protocols, and quantification techniques. We compare the clinical utility and application of hair cortisol with traditional methods of measurement while acknowledging the limitations of analysis including variations in hair growth parameters. We explore the value of hair cortisol in cases of Cushing syndrome (particularly Cyclical Cushing), Adrenal insufficiency (including Addison's disease), therapy monitoring, cardiovascular disease, stress, and mental illness.

SUMMARY

Hair cortisol provides a unique objective biomarker for the analysis of endogenous cortisol levels for not only clinical diagnostic purposes but also in research. The use of hair cortisol has great potential for advancing patient care.

The quantification of reproductive hormones in the hair of captive adult brown bears and their application as indicators of sex and reproductive state

Recognizing the potential value of steroid hormone measurements to augment non-invasive genetic sampling, we developed procedures based on enzyme-linked immunoassays to quantify reproductive steroid hormone concentrations in brown bear (Ursus arctos) hair. Then, using 94 hair samples collected from eight captive adult bears over a 2-year period, we evaluated (i) associations between hair concentrations of testosterone, progesterone, estradiol and cortisol; (ii) the effect of collecting by shaving vs. plucking; and (iii) the utility of reproductive hormone profiles to differentiate sex and reproductive state. Sample requirements (125 mg of guard hair) to assay all hormones exceeded amounts typically obtained by non-invasive sampling. Thus, broad application of this approach will require modification of non-invasive techniques to collect larger samples, use of mixed (guard and undercoat) hair samples and/or application of more sensitive laboratory procedures. Concentrations of hormones were highly correlated suggesting their sequestration in hair reflects underlying physiological processes. Marked changes in hair hormone levels during the quiescent phase of the hair cycle, coupled with the finding that progesterone concentrations, and their association with testosterone levels, differed markedly between plucked and shaved hair samples, suggests steroids sequestered in hair were likely derived from various sources, including skin. Changes in hair hormone concentrations over time, and in conjunction with key reproductive events, were similar to what has been reported concerning hormonal changes in the blood serum of brown bears. Thus, potential for the measurement of hair reproductive hormone levels to augment non-invasive genetic sampling appears compelling. Nonetheless, we are conducting additional validation studies on hair collected from free-ranging bears, representative of all sex, age and reproductive classes, to fully evaluate the utility of this approach for brown bear conservation and research.

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.

Sources of variation in hair cortisol in wild and captive non-human primates

Hair cortisol analysis is a potentially powerful tool for evaluating adrenal function and chronic stress. However, the technique has only recently been applied widely to studies of wildlife, including primates, and there are numerous practical and technical factors that should be considered to ensure good quality data and the validity of results and conclusions. Here we report on various intrinsic and extrinsic sources of variation in hair cortisol measurements in wild and captive primates. Hair samples from both wild and captive primates revealed that age and sex can affect hair cortisol concentrations; these effects need to be controlled for when making comparisons between individual animals or populations. Hair growth rates also showed considerable inter-specific variation among a number of primate species. We describe technical limitations of hair analyses and variation in cortisol concentrations as a function of asynchronous hair growth, anatomical site of collection, and the amount and numbers of hair/s used for cortisol extraction. We discuss these sources of variation and their implications for proper study design and interpretation of results.