Comparisons between salivary cortisol levels in six-months-olds and their parents

BACKGROUND: There is a close relation between the psychosocial environment of the infant--including the perception of maternal behaviour--and cortisol levels of the infant. One previous study has also demonstrated a correlation between mother and infant mean cortisol levels. In this study, this relation was further explored, also including father cortisol levels. METHODS: Saliva cortisol samples were collected from 51 six-months-olds and their parents on the same day in the morning, afternoon and evening. Analyses were performed with a radioimmunoassay technique. All mothers were at home with their child at this age and 47/51 mothers were breast feeding. RESULTS: Strong correlations were found between mother and child levels on all sampling occasions whereas weaker correlations were found between father and child levels and only in the afternoon and the evening samples. There was also a strong relation between waking up/bedtime-difference in mother and child and a weaker relation between the corresponding measure in father and child. CONCLUSIONS: The stronger mother-infant than father-infant cortisol level correlations probably mirror that mother and infant not only have genetic similarities but also have been exposed to similar environmental conditions to a higher degree than father and infant.