Cotinine, tobacco smoke, and diet: Strengthening our understanding of this biomarker in early life

There are concerns about the usefulness of cotinine and trans-3'-hydroxycotinine (3HC), as biomarkers of risk in populations with light tobacco smoke exposure. Using CHILD cohort study data, multiple linear and logistic regression was used to determine how well questionnaire responses explained urinary concentrations of cotinine and 3HC in infants, whether these concentrations predicted childhood asthmatic and allergic disease risk, and whether breastmilk facilitated nicotine exposure. Predictive models explained 31% and 41% of the variation in cotinine and 3HC, respectively. Only 23% of the infants had urinary concentrations consistent with second-hand smoke (SHS) exposure. The majority (92%) of household smoking occurred outdoors. While smokers breastfed less often, breastmilk did facilitate nicotine intake. The implications of dietary nicotine sources through breastmilk were inconclusive. Subclinical impacts and the pervasiveness of thirdhand smoke pose a challenge for public health and we should re-evaluate our use and interpretation of nicotine biomarkers in low-smoke exposure settings.