A mother who smokes and breast-feeds appears to be giving her infant a dose of nicotine that significantly interferes with the baby's sleep, according to the results of a study.
Infants spent an average of about a third less time sleeping after their mothers smoked just prior to breast-feeding, compared with when the mothers refrained, wrote Julie A. Mennella, Ph.D., and her associates at the Monell Chemical Senses Center in Philadelphia.
Nicotine is not listed as a drug that is contraindicated during breast-feeding because the benefits of breast-feeding are considered to be so great, they noted.
But the presence of nicotine in breast milk could have many adverse consequences. Mothers who smoke are known to wean their children earlier than are mothers who do not. It might be that sleep-deprived infants tend to be fussier and, if the sleep deprivation occurs because of smoking, the fussiness may stop when the mother stops breast-feeding. That in turn may reinforce a smoking mother's decision to wean. Sleep also is known to be important for learning and development, and therefore disruption of sleep caused by smoking could have lasting consequences. Lastly, adolescents whose mothers smoked during their early life are more likely to smoke, and this may sometimes be because they recognize the flavors from breast milk and come to appreciate them.
The study was conducted with 15 volunteer mother-infant pairs. The average age of the infants was 4 months. The mothers were brought into a testing center twice, and told to refrain from smoking for 12 hours before each testing session, with the last breast-feeding done about 2.5 hours before the session. During one testing session, they were allowed to smoke at least one cigarette, in a separate room from the infant, and during one session they were not (Pediatrics 2007;120:497–502).
Nicotine levels in breast milk were measured at baseline and after smoking. The infants' sleep and awake times were monitored using an ambulatory monitor for 3.5 hours. Nicotine stored in breast milk reaches peak levels about 30–60 minutes after smoking, then declines fairly rapidly.
During the smoking session, the estimated dose of nicotine delivered to the infants was a mean of 549 ng/kg, compared with 127 ng/kg during the nonsmoking session. During the nonsmoking session, the infants slept a mean of 84.5 minutes, compared with 53.4 minutes during the smoking session. All but two of the infants slept less during the smoking session.
Both active sleep and quiet sleep were reduced with smoking, and the duration of the longest bout of sleep declined from a mean of 60 minutes during the nonsmoking session to a mean of 37 minutes during the smoking session.