Professor Craig Pennell

© 2020 Elsevier Ltd Humans, similar to many other species, exhibit developmental plasticity ¿ the ability to modify the structure and function of key vital organs during specific developmental windows. Adverse exposures during these critical periods may alter organ function to enhance survival; however, over many years ¿ these alterations may predispose toward chronic disease. The hypothalamic¿pituitary¿adrenal axis plays an important role in maintaining metabolic homoeostasis and coordinating the neuropsychiatric response to stress. Decades of animal and human research suggests that the long-term function of this axis may be particularly sensitive to adverse exposures during critical developmental windows. The aim of this review is to summarise the existing knowledge of hypothalamic¿pituitary¿adrenal axis programming in humans and briefly discuss its implications for long-term health.

© 2019 American Association for Clinical Chemistry. BACKGROUND: Associations between dairy intake and body composition and cardiometabolic traits have been inconsistently observed in epidemiological studies, and the causal relationship remains ill-defined. METHODS: We performed Mendelian randomization analysis using an established genetic variant located upstream of the lactase gene (LCT-13910 C/T, rs4988235) associated with dairy intake as an instrumental variable (IV). The causal effects of dairy intake on body composition and cardiometabolic traits (lipids, glycemic traits, and inflammatory factors) were quantified by IV estimators among 182041 participants from 18 studies. RESULTS: Each 1 serving/day higher dairy intake was associated with higher lean mass [ß (SE) = 0.117 kg (0.035); P = 0.001], higher hemoglobin A1c [0.009% (0.002); P < 0.001], lower LDL [-0.014 mmol/L (0.006); P = 0.013], total cholesterol (TC) [-0.012 mmol/L (0.005); P = 0.023], and non-HDL [-0.012 mmol/L (0.005); P = 0.028]. The LCT-13910 C/T CT + TT genotype was associated with 0.214 more dairy servings/day (SE = 0.047; P < 0.001), 0.284 cm higher waist circumference (SE = 0.118; P = 0.017), 0.112 kg higher lean mass (SE = 0.027; P = 3.8 × 10-5), 0.032 mmol/L lower LDL (SE = 0.009; P = 0.001), and 0.032 mmol/L lower TC (SE = 0.010; P = 0.001). Genetically higher dairy intake was associated with increased lean mass [0.523 kg per serving/day (0.170); P = 0.002] after correction for multiple testing (0.05/18). However, we find that genetically higher dairy intake was not associated with lipids and glycemic traits. CONCLUSIONS: The present study provides evidence to support a potential causal effect of higher dairy intake on increased lean mass among adults. Our findings suggest that the observational associations of dairy intake with lipids and glycemic traits may be the result of confounding.

© 2019 American Society of Human Genetics Circulating levels of adiponectin, an adipocyte-secreted protein associated with cardiovascular and metabolic risk, are highly heritable. To gain insights into the biology that regulates adiponectin levels, we performed an exome array meta-analysis of 265,780 genetic variants in 67,739 individuals of European, Hispanic, African American, and East Asian ancestry. We identified 20 loci associated with adiponectin, including 11 that had been reported previously (p < 2 × 10-7). Comparison of exome array variants to regional linkage disequilibrium (LD) patterns and prior genome-wide association study (GWAS) results detected candidate variants (r2 > .60) spanning as much as 900 kb. To identify potential genes and mechanisms through which the previously unreported association signals act to affect adiponectin levels, we assessed cross-trait associations, expression quantitative trait loci in subcutaneous adipose, and biological pathways of nearby genes. Eight of the nine loci were also associated (p < 1 × 10-4) with at least one obesity or lipid trait. Candidate genes include PRKAR2A, PTH1R, and HDAC9, which have been suggested to play roles in adipocyte differentiation or bone marrow adipose tissue. Taken together, these findings provide further insights into the processes that influence circulating adiponectin levels.

© 2019 AMPCo Pty Ltd Objective: To compare rates of detectability of circulating Rh(D)-immunoglobulin (anti-D) at delivery with single and two-dose antenatal anti-D prophylaxis (RAADP) regimens; to compare compliance with the two regimens. Design: Open label, randomised controlled trial between May 2013 and November 2015. Setting, participants: 277 women who attended a tertiary obstetric referral hospital in Perth for antenatal care and were at least 18 years of age, less than 30 weeks pregnant and yet to receive RAADP, Rh(D)-negative (negative antibody screen), and who intended to deliver their baby at the hospital. Exclusion criteria were prior anti-D sensitisation, any contraindication of anti-D administration, and a history of isolated IgA deficiency. Interventions: One 1500¿IU anti-D dose at 28 weeks of pregnancy (single dose regimen); two doses of 625¿IU each at 28 and 34 weeks of pregnancy (two-dose regimen). Main outcome measures: The primary outcome was the proportion of women with detectable anti-D levels at delivery; the secondary outcome was compliance with the allocated RAADP regimen. Results: Circulating anti-D was detectable at delivery in a greater proportion of women in the two-dose group (111 of 129, 86%) than in the single dose group (70 of 125, 56%; P¿<¿0.001). Compliance was not significantly different between the single dose (86 of 138, 61%) and two-dose groups (70 of 139, 50%; P¿=¿0.06). Conclusions: The two-dose RAADP schedule currently recommended in Australia provides better protection against Rh(D) sensitisation than a one-dose regimen. Trial registration: Australian and New Zealand Clinical Trials Registry (ACTRN12613000661774).

© 2019, The Author(s), under exclusive licence to Springer Nature America, Inc. Body-fat distribution is a risk factor for adverse cardiovascular health consequences. We analyzed the association of body-fat distribution, assessed by waist-to-hip ratio adjusted for body mass index, with 228,985 predicted coding and splice site variants available on exome arrays in up to 344,369 individuals from five major ancestries (discovery) and 132,177 European-ancestry individuals (validation). We identified 15 common (minor allele frequency, MAF =5%) and nine low-frequency or rare (MAF <5%) coding novel variants. Pathway/gene set enrichment analyses identified lipid particle, adiponectin, abnormal white adipose tissue physiology and bone development and morphology as important contributors to fat distribution, while cross-trait associations highlight cardiometabolic traits. In functional follow-up analyses, specifically in Drosophila RNAi-knockdowns, we observed a significant increase in the total body triglyceride levels for two genes (DNAH10 and PLXND1). We implicate novel genes in fat distribution, stressing the importance of interrogating low-frequency and protein-coding variants.

© 2019, The Author(s), under exclusive licence to Springer Nature America, Inc. Birth weight variation is influenced by fetal and maternal genetic and non-genetic factors, and has been reproducibly associated with future cardio-metabolic health outcomes. In expanded genome-wide association analyses of own birth weight (n = 321,223) and offspring birth weight (n = 230,069 mothers), we identified 190 independent association signals (129 of which are novel). We used structural equation modeling to decompose the contributions of direct fetal and indirect maternal genetic effects, then applied Mendelian randomization to illuminate causal pathways. For example, both indirect maternal and direct fetal genetic effects drive the observational relationship between lower birth weight and higher later blood pressure: maternal blood pressure-raising alleles reduce offspring birth weight, but only direct fetal effects of these alleles, once inherited, increase later offspring blood pressure. Using maternal birth weight-lowering genotypes to proxy for an adverse intrauterine environment provided no evidence that it causally raises offspring blood pressure, indicating that the inverse birth weight¿blood pressure association is attributable to genetic effects, and not to intrauterine programming.

© 2019 The Author(s) 2019. Published by Oxford University Press. All rights reserved. Although hundreds of genome-wide association studies-implicated loci have been reported for adult obesity-related traits, less is known about the genetics specific for early-onset obesity and with only a few studies conducted in non-European populations to date. Searching for additional genetic variants associated with childhood obesity, we performed a trans-ancestral meta-analysis of 30 studies consisting of up to 13 005 cases (=95th percentile of body mass index (BMI) achieved 2-18 years old) and 15 599 controls (consistently <50th percentile of BMI) of European, African, North/South American and East Asian ancestry. Suggestive loci were taken forward for replication in a sample of 1888 cases and 4689 controls from seven cohorts of European and North/South American ancestry. In addition to observing 18 previously implicated BMI or obesity loci, for both early and late onset, we uncovered one completely novel locus in this trans-ancestral analysis (nearest gene, METTL15). The variant was nominally associated with only the European subgroup analysis but had a consistent direction of effect in other ethnicities. We then utilized trans-ancestral Bayesian analysis to narrow down the location of the probable causal variant at each genome-wide significant signal. Of all the fine-mapped loci, we were able to narrow down the causative variant at four known loci to fewer than 10 single nucleotide polymorphisms (SNPs) (FAIM2, GNPDA2, MC4R and SEC16B loci). In conclusion, an ethnically diverse setting has enabled us to both identify an additional pediatric obesity locus and further fine-map existing loci.

© 2018 American Society of Human Genetics C-reactive protein (CRP) is a sensitive biomarker of chronic low-grade inflammation and is associated with multiple complex diseases. The genetic determinants of chronic inflammation remain largely unknown, and the causal role of CRP in several clinical outcomes is debated. We performed two genome-wide association studies (GWASs), on HapMap and 1000 Genomes imputed data, of circulating amounts of CRP by using data from 88 studies comprising 204,402 European individuals. Additionally, we performed in silico functional analyses and Mendelian randomization analyses with several clinical outcomes. The GWAS meta-analyses of CRP revealed 58 distinct genetic loci (p < 5 × 10-8). After adjustment for body mass index in the regression analysis, the associations at all except three loci remained. The lead variants at the distinct loci explained up to 7.0% of the variance in circulating amounts of CRP. We identified 66 gene sets that were organized in two substantially correlated clusters, one mainly composed of immune pathways and the other characterized by metabolic pathways in the liver. Mendelian randomization analyses revealed a causal protective effect of CRP on schizophrenia and a risk-increasing effect on bipolar disorder. Our findings provide further insights into the biology of inflammation and could lead to interventions for treating inflammation and its clinical consequences.

OBJECTIVE: To investigate prevalence rates and the risk of ante- and intrapartum stillbirth in Western Australia with respect to maternal country of birth and ethnic origin. DESIGN, SETTING AND PARTICIPANTS: Whole population retrospective cohort analysis of de-identified, linked routinely collected birth, perinatal and mortality data for all births to non-Indigenous women in WA during 2005-2013. MAIN OUTCOME MEASURES: Crude and adjusted odds ratios (aORs) with 95% confidence intervals were estimated by logistic regression and adjusted for confounding factors, for all stillbirths, antepartum stillbirths and intrapartum stillbirths, stratified by migrant status and ethnic background (white, Asian, Indian, African, Maori, other). RESULTS: Women born overseas were more likely to have a stillbirth than Australian-born women (aOR, 1.26; 95% CI, 1.09-1.37). There was no significant difference for any type of stillbirth between Australian-born women of white and non-white backgrounds, but non-white migrant women were more likely than white migrants to have a stillbirth (OR, 1.42; 95% CI, 1.19-1.70). Compared with Australian-born women, migrants of Indian (aOR, 1.71; 95% CI, 1.17-2.47), African (aOR, 2.12; 95% CI, 1.46-3.08), and "other" ethnic origins (aOR, 1.43; 95% CI, 1.06-1.93) were more likely to have antepartum stillbirths; women of African (aOR, 5.08; 95% CI, 3.14-8.22) and "other" (aOR, 1.86; 95% CI, 1.15-3.00) background were more likely to have an intrapartum stillbirth. CONCLUSIONS: Immigrants of African or Indian background appear to be at greater risk of ante- and intrapartum stillbirth in WA. Specific strategies are needed reduce the prevalence of stillbirth in these communities.

© The Author(s) 2018. Published by Oxford University Press. All rights reserved. The ratio of the length of the index finger to that of the ring finger (2D:4D) is sexually dimorphic and is commonly used as a non-invasive biomarker of prenatal androgen exposure. Most association studies of 2D:4D ratio with a diverse range of sexspecific traits have typically involved small sample sizes and have been difficult to replicate, raising questions around the utility and precise meaning of the measure. In the largest genome-wide association meta-analysis of 2D:4D ratio to date (N=15 661, with replication N=75 821), we identified 11 loci (9 novel) explaining 3.8% of the variance in mean 2D:4D ratio. We also found weak evidence for association (b=0.06; P=0.02) between 2D:4D ratio and sensitivity to testosterone [length of the CAG microsatellite repeat in the androgen receptor (AR) gene] in females only. Furthermore, genetic variants associated with (adult) testosterone levels and/or sex hormone-binding globulin were not associated with 2D:4D ratio in our sample. Although we were unable to find strong evidence from our genetic study to support the hypothesis that 2D:4D ratio is a direct biomarker of prenatal exposure to androgens in healthy individuals, our findings do not explicitly exclude this possibility, and pathways involving testosterone may become apparent as the size of the discovery sample increases further. Our findings provide new insight into the underlying biology shaping 2D:4D variation in the general population.

© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. Background:An association between depression and obesity is well recognised, but longitudinal studies of depressive symptoms in adolescents as a predictor of body composition are lacking.Objective:We examined depressive symptoms at age 14, 17 and 20 years as predictors of lean, fat and bone mass at age 20 years in a birth cohort.Subjects/Methods:In 1161 participants (569 females) in the Western Australia Pregnancy Cohort (Raine) Study, depressive symptoms were assessed using the Beck Depression Inventory for Youth at age 14 and 17 years, and the Depression, Anxiety and Stress Scale 21 at age 20 years. Participants were further classified into two trajectories using latent class analysis: no/transient and persistent/recurrent depression. At age 20 years, lean body mass (LBM), fat body mass (FBM) and total body bone mass were measured by dual-energy X-ray absorptiometry.Results:In females, accounting for age and lifestyle factors, depression scores at age 14 and 20 years were positively associated with body weight, body mass index (BMI), FBM and % FBM (r=0.110-0.184, P<0.05) but negatively correlated with % LBM (r=-0.120, P<0.05) at age 20 years. Females in the persistent/recurrent depression trajectory (n=99) had significantly higher body weight (+5.1 kg), BMI (+1.8 kg m -2), FBM (+3.9 kg) and % FBM (+2.2%) and significantly lower % LBM (-2.2%) at age 20 years than those with no/transient depression (n=470; all P<0.05). In males, depression scores at age 17 and 20 years were negatively associated with LBM but not weight or BMI, and depression trajectory was not a predictor of body composition at age 20 years. Depression scores and trajectories did not predict bone mass in either males or females.Conclusions:Depressive symptoms and persistent/recurrent depression in adolescence are predictors of greater adiposity at age 20 years in females, but not males, but do not predict bone mass in either gender.

© 2017 The Author(s). Hair cortisol concentration (HCC) is a promising measure of long-Term hypothalamus-pituitary-Adrenal (HPA) axis activity. Previous research has suggested an association between HCC and psychological variables, and initial studies of inter-individual variance in HCC have implicated genetic factors. However, whether HCC and psychological variables share genetic risk factors remains unclear. The aims of the present twin study were to: (i) assess the heritability of HCC; (ii) estimate the phenotypic and genetic correlation between HPA axis activity and the psychological variables perceived stress, depressive symptoms, and neuroticism; using formal genetic twin models and molecular genetic methods, i.e. polygenic risk scores (PRS). HCC was measured in 671 adolescents and young adults. These included 115 monozygotic and 183 dizygotic twin-pairs. For 432 subjects PRS scores for plasma cortisol, major depression, and neuroticism were calculated using data from large genome wide association studies. The twin model revealed a heritability for HCC of 72%. No significant phenotypic or genetic correlation was found between HCC and the three psychological variables of interest. PRS did not explain variance in HCC. The present data suggest that HCC is highly heritable. However, the data do not support a strong biological link between HCC and any of the investigated psychological variables.

© 2015 The Authors. Twin studies indicate that dyscalculia (or mathematical disability) is caused partly by a genetic component, which is yet to be understood at the molecular level. Recently, a coding variant (rs133885) in the myosin-18B gene was shown to be associated with mathematical abilities with a specific effect among children with dyslexia. This association represents one of the most significant genetic associations reported to date for mathematical abilities and the only one reaching genome-wide statistical significance. We conducted a replication study in different cohorts to assess the effect of rs133885 maths-related measures. The study was conducted primarily using the Avon Longitudinal Study of Parents and Children (ALSPAC), (N=3819). We tested additional cohorts including the York Cohort, the Specific Language Impairment Consortium (SLIC) cohort and the Raine Cohort, and stratified them for a definition of dyslexia whenever possible. We did not observe any associations between rs133885 in myosin-18B and mathematical abilities among individuals with dyslexia or in the general population. Our results suggest that the myosin-18B variant is unlikely to be a main factor contributing to mathematical abilities. We could not replicate the association of the myosin-18B gene with mathematical ability.

© 2015 Straker et al. Background: Young adulthood is a critical life period for health and health behaviours. Related measurements collected before and after birth, and during childhood and adolescence can provide a life-course analysis of important factors that contribute to health and behaviour in young adulthood. The Western Australian Pregnancy Cohort (Raine) Study has collected a large number of such measurements during the fetal, perinatal, infancy, childhood and adolescence periods and plans to relate them to common health issues and behaviours in young adults, including spinal pain, asthma, sleep disorders, physical activity and sedentary behaviour and, work absenteeism and presenteeism. The aim of this paper is to describe the rationale, design and methods of the 22 year follow-up of the Raine Study cohort. Methods/Design: The Raine Study is a prospective cohort study. Participants still active in the cohort (n = 2,086) were contacted around the time of their 22nd birthday and invited to participate in the 22 year follow-up. Each was asked to complete a questionnaire, attend a research facility for physical assessment and an overnight sleep study, wear activity monitors for a week, and to maintain a sleep and activity diary over this week. The questionnaire was broad and included questions related to sociodemographics, medical history, quality of life, psychological factors, lifestyle factors, spinal pain, respiratory, sleep, activity and work factors. Physical assessments included anthropometry, blood pressure, back muscle endurance, tissue sensitivity, lung function, airway reactivity, allergic status, 3D facial photographs, cognitive function, and overnight polysomnography. Discussion: Describing the prevalence of these health issues and behaviours in young adulthood will enable better recognition of the issues and planning of health care resources. Providing a detailed description of the phenotype of these issues will provide valuable information to help educate health professionals of the needs of young adults. Understanding the life-course risk factors of health issues and behaviours in young adulthood will have important health planning implications, supporting the development of targeted interventions to improve current health status and reduce the onset and development of further ill-health across adulthood.

Summary: The relationships between fat mass and bone mass in young adults are unclear. In 1,183 young Australians, lean body mass had a strong positive relationship with total body bone mass in both genders. Fat mass was a positive predictor of total body bone mass in females, with weaker association in males. Introduction: Body weight and lean body mass are established as major determinants of bone mass, but the relationships between fat mass (including visceral fat) and peak bone mass in young adults are unclear. The aim of this study was to evaluate the associations between bone mass in young adults and three body composition measurements: lean body mass, fat mass and trunk-to-limb fat mass ratio (a surrogate measure of visceral fat). Methods: Study participants were 574 women and 609 men aged 19-22 years from the Raine study. Body composition, total body bone mineral content (TBBMC), bone area and areal bone mineral density (TBBMD) were measured using DXA. Results: In multivariate linear regression models with height, lean body mass, fat mass and trunk-to-limb fat mass ratio as predictor variables, lean mass was uniquely associated with the largest proportion of variance of TBBMC and TBBMD in males (semi-partial R 2 0.275 and 0.345, respectively) and TBBMC in females (semi-partial R 2 0.183). Fat mass was a more important predictor of TBBMC and TBBMD in females (semi-partial R 2 0.126 and 0.039, respectively) than males (semi-partial R 2 0.006 and 0.018, respectively). Trunk-to-limb fat mass ratio had a weak, negative association with TBBMC and bone area in both genders (semi-partial R 2 0.004 to 0.034). Conclusions: Lean body mass has strong positive relationship with total body bone mass in both genders. Fat mass may play a positive role in peak bone mass attainment in women but the association was weaker in men; different fat compartments may have different effects. © 2014 International Osteoporosis Foundation and National Osteoporosis Foundation.

Objective Hypertension in pregnancy and preeclampsia have been linked to poor outcomes in cognitive, mental and psychomotor development; however, few longitudinal studies have researched their effect on offspring motor development, particularly in late childhood and adolescence. The purpose of this study was to determine if maternal hypertensive diseases during pregnancy are a risk factor for compromised motor development at 10, 14, and 17 years. Study design Longitudinal cohort study using data from the Western Australian Pregnancy Cohort Study (Raine). Main outcome measure Offspring (n = 2868) were classified by their maternal blood pressure profiles during pregnancy: normotension (n = 2133), hypertension (n = 626) and preeclampsia (n = 109). Offspring motor development, at 10, 14, and 17 years was measured by the Neuromuscular Developmental Index (NDI) of the McCarron Assessment of Motor Development (MAND). Methods Linear mixed models were used to compare outcomes between pregnancy groups. Results Offspring from pregnancies complicated by preeclampsia had poorer motor outcomes at all ages than offspring from either normotensive mothers (p = 0.001) or those with hypertension (p = 0.002). Conclusion Hypertensive diseases during pregnancy, in particular preeclampsia, have long term and possibly permanent consequences for motor development of offspring. © 2014 International Society for the Study of Hypertension in Pregnancy Published by Elsevier B.V. All rights reserved.

© 2014 Macmillan Publishers Limited. All rights reserved. Twin studies suggest that expressive vocabulary at ~24 months is modestly heritable. However, the genes influencing this early linguistic phenotype are unknown. Here we conduct a genome-wide screen and follow-up study of expressive vocabulary in toddlers of European descent from up to four studies of the EArly Genetics and Lifecourse Epidemiology consortium, analysing an early (15-18 months, 'one-word stage', NTotal=8,889) and a later (24-30 months, 'two-word stage', NTotal=10,819) phase of language acquisition. For the early phase, one single-nucleotide polymorphism (rs7642482) at 3p12.3 near ROBO2, encoding a conserved axon-binding receptor, reaches the genome-wide significance level (P=1.3×10-8) in the combined sample. This association links language-related common genetic variation in the general population to a potential autism susceptibility locus and a linkage region for dyslexia, speech-sound disorder and reading. The contribution of common genetic influences is, although modest, supported by genome-wide complex trait analysis (meta-GCTA h15-18-months2=0.13, meta-GCTA h24-30-months2 =0.14) and in concordance with additional twin analysis (5,733 pairs of European descent, h24-months2=0.20).

Objective To evaluate the risk of placenta praevia accreta following primary (first) elective or primary emergency caesarean section in a pregnancy complicated by placenta praevia. Design Retrospective matched case-control study, employing variable matching. Setting Tertiary referral centre between 1993 and 2008. Population Sixty-five cases and 102 controls were used for the analysis from a total of 82 667 births during the study period. Methods Relevant data were abstracted from clinical records. Matching of cases with controls was based on co-existing placenta praevia, number of previous caesarean sections, and age, with one or two controls per case. Results are presented as odds ratios (ORs) with 95% confidence intervals (95% CIs). Main outcome measures Placenta accreta in a pregnancy complicated by placenta praevia following a primary elective or emergency caesarean section, and morbidity associated with pregnancies complicated by placenta accreta. Results Significantly more cases than controls had an elective caesarean section for their primary caesarean delivery (46.2 versus 18.6%; P < 0.001). There were no differences between groups for previous pregnancy loss, uterine surgery, and vaginal delivery, before or after the primary caesarean section. Compared with primary emergency caesarean section, primary elective caesarean section significantly increased the risk of placenta accreta in a subsequent pregnancy in the presence of placenta praevia (OR 3.00; 95% CI 1.47-6.12; P = 0.025). Conclusions Our results suggest that women with a primary elective caesarean section without labour are more likely, compared with those undergoing primary emergency caesarean section with labour, to develop an accreta in a subsequent pregnancy with placenta praevia. © 2013 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2013 RCOG.

Dysfunctional regulation of the hypothalamic-pituitary-adrenal (HPA) axis has been proposed as an important biological mechanism underlying stress-related diseases; however, a better understanding of the interlinked neuroendocrine events driving the release of cortisol by this stress axis is essential for progress in preventing or halting irreversible development of adverse HPA-function. We aimed to investigate basal HPA-activity in a normal population in late adolescence, the time of life believed to overlap with HPA-axis maturation and establishment of a lasting set point level of HPA function. A total of 1258 participants (mean age 16.6 years) recruited from the Western Australian Pregnancy (Raine) Cohort provided fasting morning blood and saliva samples for basal HPA activity assessment. Irrespective of gender, linear regression modelling identified a positive correlation between the main components of the HPA-cascade of events, ACTH, total cortisol and free cortisol in saliva. Corticosteroid binding globulin (CBG) was inversely associated with free cortisol in saliva, an effect most clearly observed in boys. ACTH levels were lower, but cortisol levels were higher in girls than in boys. Girls may also be exposed to more bioactive cortisol, based on higher average free cortisol measured in saliva at awakening. These relatively higher female free cortisol levels were significantly reduced by oral contraceptive use, eliminating the gender specific difference in salivary cortisol. Free plasma cortisol, calculated from total circulating cortisol and CBG concentrations, was also significantly reduced in girls using oral contraceptives, possibly via an enhancing effect of oral contraceptives on blood CBG content. This study highlights a clear gender difference in HPA activity under non-stressful natural conditions. This finding may be relevant for research into sex-specific stress-related diseases with a typical onset in late adolescence. © 2012 Elsevier Ltd.