Individual differences in salivary cortisol and alpha-amylase in mothers and their infants: Relation to tobacco smoke exposure

Tobacco smoke exposure affects the activity of both the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS). Statistics reveal 41 million children in the U.S. are regularly exposed to tobacco smoke, but we know little about the effects of environmental tobacco smoke exposure on HPA and SNS activity in early childhood. This study assayed cotinine (a metabolite of nicotine), cortisol, and alpha-amylase (sAA) in the saliva of mother-infant dyads from 197 low income and ethnically diverse families. The dyads were identified as tobacco smoke exposed (N = 82) or nonexposed (N = 115) based on maternal self-reports of smoking and salivary cotinine levels greater or less than 10 ng/ml. As expected, higher rates of maternal smoking behavior were associated with higher levels of cotinine in mothers' and their infants' saliva. On average, smoking mothers' salivary cotinine levels were 281 times higher compared to their nonsmoking counterparts, and 23 times higher compared to their own infant's salivary cotinine levels. Infants of smoking mothers had salivary cotinine levels that were four times higher than infants with nonsmoking mothers. Mothers who smoked had higher salivary cortisol levels and lower sAA activity compared to nonsmoking mothers. There were no associations between maternal smoking behavior, infant's salivary cotinine levels, or tobacco exposure group, and cortisol or sAA measured in infant's saliva. The findings are discussed in relation to the influence of smoking tobacco on the validity of salivary biomarkers of stress.