Internalizing disposition and preschool children's cortisol fluctuations.
BACKGROUND
Research on the impact of childcare suggested that young children's cortisol tends to increase or remain 'flat' across the day while their cortisol levels follow the typical circadian decrease between mid-morning and mid-afternoon at home. However, studies are needed to investigate what is happening to cortisol levels and whether individual variation exists in the cortisol rhythm in childcare.


METHODS
Internalizing disposition was examined as a possible moderator of cortisol-linked stress response of young children in full-time, centre-based childcare. Ambulatory salivary sampling for cortisol was performed on 37 preschoolers at four different times for 10 consecutive school days. In order to test the interaction effect of internalizing disposition on cortisol levels, children were divided into four groups--the most internalizing group, the least internalizing group, and two groups in between, based on teacher-rated 'approach' scores.


RESULTS
Repeated measure analyses of variance with polynomial contrast for time indicated that (1) a linear trend of significant increase between mid-morning and mid-afternoon exists for all children without group interactions; (2) quadratic and cubic trends exist and the interaction effects among the groups are significant, meaning the four groups are different in fluctuation pattern. Further analyses demonstrated that (1) the least internalizing children showed significant decreases in cortisol levels from morning to noon and after nap, although there is a considerable increase after lunch, (2) cortisol levels of the other three groups across the day fit the pattern of upward curve.


CONCLUSIONS
The tradition of the field in comparing mid-morning and mid-afternoon levels of cortisol as an indicator of childcare effect may not reflect individual variation in the fluctuation patterns of cortisol. Moderating effect of child characteristics needs to be considered in future research of childcare effect.
Department of Child Care and Education, Hungkuang University, Taichung, Taiwan. ishien@sunrise.hk.edu.tw
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D000704:Analysis of Variance; D015415:Biomarkers / Q000378:metabolism; D002648:Child; D002652:Child Behavior / Q000502:physiology*; D002656:Child Day Care Centers; D002675:Child, Preschool; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D008297:Male; D010913:Pituitary-Adrenal System / Q000502:physiology*; D012463:Saliva / Q000737:chemistry; D013624:Taiwan; D013694:Temperament / Q000502:physiology*
D015415:Biomarkers; D006854:Hydrocortisone