Relationships between nicotine and cotinine concentrations in maternal milk and saliva

Aim Breastfeeding may be impaired due to nicotine excreted into the milk of smoking mothers. We investigated the relationships between nicotine and cotinine concentrations in maternal milk and saliva among breastfeeding smokers. Methods The 41 mothers reported their cigarette consumption between waking up and milk and saliva sampling. The median sampling time took place four days after delivery. Nicotine and cotinine concentrations were determined by liquid chromatography and UV detection, after a single-step saliva or three-step milk liquid-to-liquid extraction. Results The median (interquartile range) concentrations in milk and saliva were 7 (6–22) and 27 (4–207) μg/L for nicotine and 24 (5–111) and 22 (4–120) μg/L for cotinine, respectively. Milk cotinine was positively associated with saliva cotinine (p < 0.0001) and cigarette consumption (p = 0.039) and inversely associated with the time since the last cigarette (p = 0.0004, model R2 = 0.90). Milk nicotine was associated with saliva nicotine concentration (p = 0.0017) and cigarette consumption (p = 0.0023, model R2 = 0.63). Conclusion Saliva nicotine concentration was not a very good estimate of milk nicotine concentration in breastfeeding mothers. Saliva cotinine concentration may be used instead of milk cotinine concentration to estimate tobacco or nicotine exposure among breastfed neonates or infants.