Feeding and urine cotinine values in babies whose mothers smoke.

In Canada, 8% to 20% of infants are breast-fed by mothers who smoke. To determine whether breast-feeding increases infants' exposure to tobacco smoke products, urinary cotinine excretion was measured in 172 babies, 33 of whom were breast-fed. A milk sample was taken from the mothers who were breast-feeding, and cotinine was measured with gas chromatography. The breast-fed babies had a median cotinine to creatinine ratio of 433 ng/mg, whereas the bottle-fed babies' median was 200 ng/mg (P less than 10(-4)). Similar differences were observed after adjustment for the number of cigarettes smoked by the mother and by other smokers in the home in the previous 24 hours. The correlation coefficient between the number of cigarettes smoked by the mother and the breast milk cotinine concentration was significant (r = .69, P = 2 X 10(-4)). Moreover, urine cotinine values from the breast-fed babies increased with higher concentrations of cotinine in the mother's milk (r = .56, P = .02). These results provide evidence that breast-feeding increases exposure to tobacco smoke components in infants whose mothers smoke. This is yet another argument for strongly encouraging women who smoke to stop smoking during pregnancy and lactation.