Nicotine and cotinine concentrations in the milk of smoking mothers: influence of cigarette consumption and diurnal variation.

The relationship between nicotine and cotinine concentrations in mother's milk (including 24 h profiles) and the number of cigarettes consumed was studied. A total of 206 milk samples were collected from 34 nursing, smoking mothers. The mothers were distributed into three groups: Group I (1-10 cigarettes/day), group II (11-20 cigarettes/day) and group III (21-40 cigarettes/day). Milk samples from all nursing periods of a 24 h interval were collected. Nicotine and cotinine concentrations were measured by specific gas chromatographic techniques. The average milk nicotine and cotinine concentrations over a 24 h interval in the three groups were as follows: group I, 18 +/- 16 and 76 +/- 33 ng/ml; group II, 28 +/- 21 and 125 +/- 60 ng/ml; group III, 48 +/- 25 and 230 +/- 62 ng/ml (means +/- SD). Over a time interval of 24 h the nicotine concentrations varied greatly in the milk of smoking mothers, while the cotinine concentrations remained relatively constant. Because of the great intra- and inter-individual variations in the nicotine concentrations, the influence of the number of cigarettes smoked on the nicotine concentration in milk was most apparent if nicotine concentrations were measured repeatedly over a prolonged time interval. Our results indicate that the exposure of the nursed infant to nicotine and cotinine via milk depends on the daily cigarette consumption but also on individual smoking habits; the time of smoking, smoking frequency prior to nursing, and the time interval between nursing and the last cigarette.