Dr Julie Mennella, Monell Chemical Senses Centre
Chris - Tell us about this study that you've done on mothers that are breastfeeding but smoking as well.
Julie - Well, there really hasn't been a lot of research on the consequences of smoking while you're breastfeeding, and there have been changes in policy here and one of the questions that we had was, what are the short term effects? What we found is that if a mother smokes 1-2 cigarettes and breastfeeds the baby, even within a few hours after breastfeeding we find drastic differences in the baby's sleeping patterns. The baby is sleepless, they wake up from their nap sooner, and the greater the disruption in sleep correlated with how much nicotine the baby ingested.
Chris - When you say the baby slept less, how much less? Was it a significant amount?
Julie - Yes. What we did was we looked at the baby on two days, one day the mothers refrained from smoking and one day the mothers smoked, though not in the presence of the baby. We found that the amount of time the baby slept was reduced by almost a half hour, in just that three and a half hour period.
Chris - So that's a reduction of a good 40% isn't it?
Julie - Sure.
Chris - So if the babies are sleeping 40% less, are they catching up some other time in the day?
Julie - That's great question that we don't have the answer to. One of the interesting things is in mothers who breastfeed and smoke there's been a number of studies that show that [their babies are] more colicy and more active, and maybe this is one of the consequences of the nicotine exposure. We don't have the answers for cigarettes but what we do know if that we also get sleep disruption when alcohol is also transmitted to human milk. What we can learn from those studies is that if the mother doesn't continue to drink the babies do compensate for it later on in the night, but the key is that the baby can't be exposed to nicotine again.
Chris - Now, I think there have been some studies that have shown that if you are exposed to nicotine as a young baby, there's an association with having learning difficulties or behavioural problems later on in life. Is that correct?
Julie - Yeah, and most of those studies were looking at the relationship between nicotine exposure during pregnancy and then learning disabilities during childhood. There's been very few studies that have factored in the exposure during breastfeeding. One of the things is that mothers can reduce the amount of nicotine that babies are exposed to by timing it, so unlike that which occurs during pregnancy, babies would sleep less. Getting back to your question though about learning disabilities, one of the functions of sleep is for memory consolidation and the forming of new memories, and so disruptions in sleep may be the mechanisms underlying that.
Chris - It's quite a significant difference in the amount of sleep they're getting though, do you actually think if you did this on large numbers of people you would see this effect maintained? You looked at fifteen mothers, so do you think that's a big enough number to draw conclusions from?
Julie - Well, this study is what one calls a 'within subject', so you look at each baby on the day that their mothers don't smoke and compare it to when they did, so that's quite a powerful design. We know that there are colic problems in infants, we know that nicotine is a known stimulant that has effects on sleep in adults and so this is really consistent with a large body of research. But as now, if you think of the infant you would expect a greater result because the liver is not as mature and they're not able to break down the nicotine as well. So I would say that it's consistent with a large body of literature and also literature in other animals which shows that nicotine is a stimulant and disrupts sleep.
Dave - If the mothers are addicted to nicotine, would they be behaving differently when they haven't had a cigarette, and would that effect the babies at all?
Julie - Good question, there hasn't been a lot of research on that at all. So I dont have the answer to that one for you.
Chris - And do you think that as these babies are being exposed to nicotine, as you've shown it in large amount in breast milk, are they more likely to go on and smoke when they get older?
Julie - I'd like to think of it the opposite way too, just like with alcohol, with nicotine not every child of a mother who smokes or drinks is going to become a smoker or a drinker. What is it about the role of early experience that puts one child on one trajectory and another on another? We don't have the answers to that. But I would add that unlike that which occurs during pregnancy, a lactating mother can minimise the amount of nicotine that gets to her baby if she does smoke, so that's part of the goal too in talking to researchers to get that type of information out there.
Chris - If a lady wants to breastfeed, because we don't want to put people off from breastfeeding because we know that has the best outcome for babies, it's the best thing to do; so what should a woman do if she wants to be able to smoke and breastfeed her baby with the minimum risk?
Julie - I couldn't agree with you more and I want to state that over and over; Breastfeeding is the ideal way to not only feed, but to nurture infants. What's interesting is that women tend to cut down or actually stop smoking when they're pregnant only to start creeping up back again later. The number one thing is try not to stop smoking again, having a husband who smokes contributes to the relapse, so I think fathers have got to take some responsibility here and there really has been very little research ion what's the most effective intervention to meet the needs of mothers for smoking cessation. The second thing is minimise the babies' exposure, don't smoke in the baby's presence, in confined area like the car or home where the windows are closed, and also, what I want to tell them is what the time course is; When you smoke a cigarette the nicotine levels in your milk are going to peak about a half hour to an hour after you smoke and then by three hours they're really going to be at low levels. So you want to time your breast feeds to minimise the baby's exposure, so wait a couple of hours after you smoke, you can imagine just breastfeeding the baby and then having a cigarette if the baby feeds every 3-4 hours.