Nicotine in breast milk disrupts babies sleep patterns and shortens naps by one-third, according to a new study.

"Infants spent less time sleeping overall and woke up from naps sooner when their mothers smoked prior to breast-feeding," said study lead author Julie A. Mennella, PhD, a psychobiologist at the Monell Chemical Senses Center, a nonprofit institute that researches the senses of taste, smell and chemical irritation.

Writing in the journal Pediatrics, Dr. Mennella and colleagues argued that these results should lead to further research on the impact of nicotine on infant development. Many women who quit smoking during pregnancy begin again while breast-feeding their infant, the researchers said.

"Because nicotine is not contraindicated during lactation, mothers may believe that smoking while breast-feeding will not harm their child as long as the child is not exposed to passive smoke. However, there has been very little research on either short- or long-term effects of nicotine delivered through breast milk," said Dr. Mennella.

The Study

The team measured the feeding and sleeping patterns of 15 breast-fed infants over three and a half hours on two separate days. The infants were between two months and seven months old. All the mothers were current smokers who had abstained from smoking for at least 12 hours before the observation periods.

The mothers smoked one to three cigarettes before the first observation period and didn't smoke anything before the second period. On both occasions, the mothers breast-fed their infants on demand during the observation period. Following each feeding, the mothers laid the infants down in a cot or on the floor.

Researchers monitored the babies with an actigraph, a portable device that records sleep and activity. Levels of nicotine and cotinine, a chemical that is produced by the body from nicotine, were measured in breast milk samples provided by the mothers before each feeding.

The Results

Babies whose mothers smoked before the observation period napped for 53 minutes compared to 84 minutes of napping among babies whose mothers did not smoke. The 37% reduction in total sleep time was due to a shortening of the longest nap and to reductions in the amount of time spent in both active and quiet sleep.

Researchers noted that the infants consumed the same amount of breast milk during each observation period, suggesting that they tolerated the milk of women who smoked.

Timing Breast-Feeding

Previous research by Dr. Mennella's team had shown that nicotine levels peak in breast milk 30 minutes to 60 minutes after smoking one to two cigarettes and are gone after three hours, suggesting that mothers can time their smoking and breast-feeding opportunities.

Additional research is needed to fully understand the impact of nicotine on infant development, Dr. Mennella said.

Smoking May Program Children to Smoke

Smoking during pregnancy may "program" unborn children to become smokers.

Recent study: Children whose mothers smoked while they were pregnant were three times more likely to begin smoking by age 14-and twice as likely to start after age 14-as children of women who did not smoke during pregnancy. Children of women who either never smoked or who quit during pregnancy but returned to smoking afterward were less likely to begin smoking.

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