Early stress, cortisol in hair and health among children in different psychosocial environments
Abstract: Psychosocial circumstances during early life are increasingly recognized as crucial, not only for the growing individual but also for health throughout life. A possible mechanism could be physiologic dysregulation due to stress. Cortisol in hair is a new biomarker that allows assessment of long-term activity of the hypothalamic-pituitary-adrenal axis.The objective of this thesis was to investigate the relationship between early stress, levels of cortisol in hair and health among children in different psycho-social environments.The ABIS-study is a prospective population-based cohort study of every child born in southeast Sweden between Oct 1 1997 and Oct 1 1999 (N=21,700) in which approximately 17,000 families (79%) participated. The studies presented in Papers I, III and IV were based on ABIS data on children aged 1, 3, 5 and 8 years concerning stress related psychosocial variables as well as hair samples and diabetes related autoantibodies. Papers I and IV compared a subsample (n=2,448) from two different social environments. Paper III consisted of a subsample of 100 children as well as their mothers. Paper II covered 99 university students.Paper I showed that the risk for diabetes-related autoantibodies, both against GADA and IAG2A (>95% cut off), was significantly higher (p<0.0001) among children from the blue-collar than from the white-collar city. This difference persisted still after adjustment for other previously documented risk factors. In paper II the method of measuring cortisol concentrations in hair was developed and mean cortisol levels were significantly related to serious life events (p=0.045) among the students. Paper III demonstrated that, in children from one to eight years of age, cortisol levels in hair decreased over time and correlated to each succeeding age, between years 1 and 3 (r=0.30,p=0.002), 3 and 5 (r=0.39, p=0.001), and 5 and 8 (r=0.44, p=0.001). Repeated measures gave a significant linear association over time (p=0.001). Maternal hair cortisol levels during the second and third trimester and child hair cortisol at year 1 and 3 was also significantly associated. Paper IV showed that children with prenatal psychosocial exposures had higher infant cortisol levels in hair (B=0.40, p<0.0001, adjusted for gender and size for gestational age) in a dose-response manner and were more often (p?0.05) affected by 12 of the 14 most common childhood diagnoses with a general pattern of rising ORs.In conclusion, the findings in this thesis showed that children born into an environment fraught with adverse psychosocial exposures seem to have an increased hypothalamic-pituitary-adrenal axis activity. It appears to be persistent throughout early childhood and affect health negatively, as evidenced through common childhood diseases and levels of autoantibodies. A widespread and dose response-like effect of adverse psychosocial circumstances was seen on the different outcomes studied throughout this thesis. This supports the model of physiologic dysregulation as a plausible pathway in how the duration and number of early detrimental exposures act as a trajectory to health disparities. Knowledge of these relationships could be valuable in selecting preventive measures, not least in primary care. Moreover, given the prolonged nature of exposure to a stressful social environment, the novel biomarker of cortisol in hair appears to be a useful aid in studies on how long-term stress affects health and may be particularly relevant when applied to research on children.
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