Background: The developmental origins hypothesis suggests that pre- and postnatal exposures may influence vulnerability to later disease. The hypothalamic-pituitary-adrenal (HPA) axis is one pathway by which this may occur. Analyses were conducted in the Barry Caerphilly Growth (BCG) cohort to explore whether the postnatal exposure of childhood infections was related to HPA axis activity in adulthood.
Methods: Detailed data on type and frequency of illnesses were collected in the first 5 years of life. At the recent follow-up of this cohort (N=566; mean age of participants=25 years) three salivary cortisol samples were taken: two fasting samples in the morning (within 30 min of arrival at the study site and after venesection and cognitive test procedures) and one evening sample (2200 h). These data were transformed to provide AUCi and AUCg (indices reflecting axis reactivity and total hormonal output, respectively).
Findings: Negative associations were evident between number of upper respiratory illnesses and adult cortisol (as captured by the second morning sample, evening sample and AUCg). These relationships remained after controlling for other potential prenatal, postnatal and adult determinants. These associations were not observed for gastrointestinal illnesses suggesting that confounding by socioeconomic factors is unlikely to be the explanation.
Conclusions: Childhood respiratory illnesses were associated with reduced HPA axis activity in adulthood. Further follow-ups will determine whether this pattern of activity influences vulnerability to diseases associated with HPA regulation.