title: Diurnal cortisol rhythms and child growth: exploring the life history consequences of HPA activation among the Tsimane'.
abstract: OBJECTIVE
  Although psychosocial stress has also been implicated as a contributor to growth failure by imposing energetic constraints during development, the direct physiological pathways by which these life history trade-offs are imposed are not well understood. This study explores associations between diurnal cortisol rhythms and differential patterns of linear child growth among the Tsimane, a horticulturalist and foraging society in the Bolivian Amazon.
  
  
  METHODS
  Waking and bedtime salivary cortisol samples (n = 243) were collected from 53 Tsimane' children ages 1.6-6 over 3 days as part of a larger study of developmental trajectories in hypothalamic-pituitary-adrenal axis dynamics. Anthropometric measurements and survey data were collected in conjunction with the Tsimane' Amazonian panel study (TAPS).
  
  
  RESULTS
  Among children under the age of 6, diurnal rhythms in stunted versus nonstunted children vary dramatically: stunted children display elevated cortisol at both the AM (P = 0.03) and PM (P = 0.02) collection points. Multilevel regression analysis demonstrates an inverse relationship between cortisol and height-for-age z-score status (P = 0.00), which is mediated, in part, by infection (P = 0.00), and is strongest among male children (n.s.). Moreover, the poorest statural growth is exhibited among children with high cortisol living in more acculturated Tsimane' communities, a proxy for a more adverse developmental milieu.
  
  
  CONCLUSIONS
  This study reports a small, but significant, life history cost of elevated diurnal cortisol rhythms on linear growth among Tsimane' children, and provides critical insight into the developmental origins of health differentials among an indigenous Amazonian population experiencing rapid lifestyle changes.
authors.affiliation: Department of Anthropology, University of Massachusetts Boston, Boston, Massachusetts 02125, USA. colleen.nyberg@umb.edu
authors.forename: Colleen H
authors.initials: CH
authors.lastname: Nyberg
authors.forename: William R
authors.initials: WR
authors.lastname: Leonard
authors.forename: Susan
authors.initials: S
authors.lastname: Tanner
authors.forename: Thomas
authors.initials: T
authors.lastname: McDade
authors.forename: Tomas
authors.initials: T
authors.lastname: Huanca
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Godoy
mesh_terms: D000069:Acculturation; D001827:Body Height; D001838:Bolivia; D002675:Child, Preschool; D002940:Circadian Rhythm; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism*; D007199:Indians, South American / Q000523:psychology; D007223:Infant; D008019:Life Style; D008137:Longitudinal Studies; D008297:Male; D010913:Pituitary-Adrenal System / Q000378:metabolism*; D012463:Saliva / Q000737:chemistry; D012737:Sex Factors; D013312:Stress, Physiological; D013315:Stress, Psychological
chemical_list: D006854:Hydrocortisone