+ Models PNEC-2241; No. of Pages 8 Please cite this article in press as: Stalder, T., et al., The cortisol awakening response in infants: Ontogeny and associations with development-related variables. Psychoneuroendocrinology (2012), http://dx.doi.org/10.1016/j.psyneuen.2012.07.015 The cortisol awakening response in infants: Ontogeny and associations with development-related variables Tobias Stalder a,1, * , Damaris Ba ¨umler a,1 , Robert Miller a , Nina Alexander a , Matthias Kliegel b , Clemens Kirschbaum a a Technische Universita¨t Dresden, Department of Psychology, Dresden, Germany b University of Geneva, Department of Psychology, Geneva, Switzerland Received 4 April 2012; received in revised form 24 July 2012; accepted 25 July 2012 1. Introduction The cortisol awakening response (CAR), the marked increase of cortisol secretion following morning awakening, is fre- quently assessed in psychoneuroendocrinological research (see Fries et al., 2009; Clow et al., 2010). Despite a growing body of research examining the CAR in relation to different psychosocial and health-related variables, fundamental Psychoneuroendocrinology (2012) xxx, xxx—xxx KEYWORDS Cortisol awakening response; Ontogeny; Development; Infant; Sleep Summary The cortisol awakening response (CAR) is a frequently used measure in psychoneur- oendocrinological research, however, some of its more fundamental aspects still require atten- tion. An important question in this respect concerns the ontogeny of the CAR. Data from two recent reports suggest that the CAR may only emerge relatively late during child development (16 months of age). However, as both enquiries did not use objective means of verifying participant adherence or infants’ awakening times, it is unclear whether methodological factors may have contributed to these results. Here, we report data from a study on 33 infants aged 2—12 months with close care being taken to ensure the accuracy of sampling times by using wrist actigraphy and electronic monitoring containers. Salivary cortisol levels were assessed at 0 and 30 min post-awakening over three study days. Results revealed evidence for a significant CAR (2.5 nmol/L) in 32 (out of 33) infants and on a total 86.9% of study days, with a marked magnitude of the CAR across infants (mean estimated increase = 12.54 nmol/L). In addition, the cortisol level on awakening and the CAR were found to be associated with different aspects of infant’s physical and sleep-related development as well as with their weight and body mass index (BMI) at birth. Contrary to previous reports, the current results thus indicate that the ontogeny of the CAR occurs at an early stage of development and that it is present from as early as two months of life. The data also suggest that post-awakening cortisol secretion may undergo considerable changes during the first year of life associated with different aspects of infant development. # 2012 Elsevier Ltd. All rights reserved. * Corresponding author at: Technische Universita ¨t Dresden, De- partment of Psychology, Andreas-Schubert-Bau, Zellescher Weg 19, 01069 Dresden, Germany. Tel.: +49 351 463 39678; fax: +49 351 463 37274. E-mail addresses: stalder@biopsych.tu-dresden.de, tobias.stalder@googlemail.com (T. Stalder). 1 Both authors have contributed equally to this manuscript. Available online at www.sciencedirect.com j our na l h omepa g e: www.e lse vie r.c om/l oca te/ psyne ue n 0306-4530/$ — see front matter # 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.psyneuen.2012.07.015