If anyone needs a little caffeine, it’s a new mom. My labor with Cee took me through two mostly sleepless nights, and when she finally arrived, we took a little time to nurse and get to know one another, and then our whole little family took a long nap. When we woke up, the first thing I did was send my husband to get me a latte. The second thing I did was breastfeed my new baby again. That dose of caffeine felt like good therapy to me, but what about for Cee? Was it good for her?

A few weeks ago, I wrote about the safety of caffeine in pregnancy, and several readers wanted to know about the postnatal effects of caffeine – how mom’s caffeine intake might affect her breastfed baby. I promised to take a look at the literature and report back, and so here we are.

When you drink a cup of coffee, how much caffeine ends up in your breast milk?

Several studies have examined this question, and although they are small, they give us a general idea of the transfer of caffeine from mom’s blood to her milk. After a cup of coffee, caffeine is rapidly absorbed into mom’s blood and then passively diffuses across the epithelial layers of the mammary gland. Caffeine appears in milk within 15 minutes of consumption and peaks within an hour. The concentration of caffeine in breast milk ends up being about 80–90% of that in mom’s plasma. However, taking into account the amount of breast milk consumed and adjusting for body weight, studies have estimated that the infant receives no more than 10% of the maternal dose of caffeine, and likely much less (see here, here, and here).

Is this amount of caffeine safe for a baby?

Just because levels of caffeine in breast milk are low relative to what adults normally consume doesn’t mean that these amounts are necessarily safe to a baby. Another important factor is how efficiently a baby can metabolize caffeine, and it turns out that newborn caffeine metabolism is really slow. Whereas the half-life of caffeine in adults is around 2-6 hours, it is an average of 3-4 days in newborns and can be even slower in premature babies. In other words, a morning cup of coffee for mom will easily clear her blood by bedtime, but caffeine may linger in her breastfed newborn for much longer. Metabolism gradually ramps up as the baby matures and the necessary enzyme levels come on board, and most babies can metabolize caffeine at rates similar to adults by 5-6 months of age.

However, there is a lot of baby-to-baby variation in caffeine metabolism. For example, in a study measuring the half-life of caffeine in 5 babies between 6 and 8 weeks of age, results ranged from 8 to 41 hours. Mom’s cup of coffee is probably more likely to have an effect on the 41-hour baby than the 8-hour baby.

There’s some evidence that your caffeine consumption in pregnancy might impact your baby’s ability metabolize caffeine. A 2010 study measured the behavior of 13 fetuses at 36-38 weeks of pregnancy. Moms were asked to track their caffeine intake for 1 week, and this was verified with blood caffeine measurements. The moms were then asked to avoid all caffeine for 2 days, after which they all drank 2 cups of black coffee (300 mg caffeine). After this standard dose of caffeine, fetuses of mothers who were usually high caffeine consumers showed no change in behavior. However, those whose moms usually consumed little to no caffeine showed a clear response to the coffee. They were more wakeful, moved more, and had a lower basal heart rate but with greater variation. This is a small study, and we don’t know if this effect continues after birth, but it suggests that babies that are exposed to some caffeine in utero may be more tolerant of caffeine.

The few studies that have actually looked at breastfed babies’ behavior under the influence of caffeine are reassuring. A 1984 study included 11 mom-baby pairs (3-10 weeks of age) in a crossover design, asking moms to drink 5 cups of decaffeinated coffee per day for 5 days and then 5 cups of caffeinated coffee (500 mg) per day for another 5 days. During the caffeinated period, the infants absorbed caffeine as expected, but there was no difference in their heart rates or sleep times. A more recent study, conducted in Brazil and published in Pediatrics in 2012, carefully tracked maternal caffeine intake through pregnancy and during breastfeeding. The mothers of 885 3-month-old infants recorded their babies’ sleeping patterns for 15 days. There were no significant differences in the sleep patterns of the babies based on maternal caffeine consumption, even in moms consuming more than 300 mg per day. (For estimated caffeine content of various drinks and medications, see the table in my previous post on caffeine safety in pregnancy.)

Caffeine is also routinely used to treat apnea in premature babies. It’s one of the 10 most frequently prescribed medications in the NICU, and this use gives us a little more information about safety. The daily dose used in the NICU, often continued for several weeks, is as much as 10-20 times the amount absorbed by a breastfed baby whose mom drinks a single cup of coffee, and this is on top of the slowed metabolism of caffeine in premature babies. Side effects are sometimes seen at this dose: increased heart rate, trouble feeding, and slower weight gain. However, a randomized controlled trial of more than 2000 infants found that caffeine was effective at reducing apnea and that it also reduced the incidence of cerebral palsy and cognitive delay at 18-21 months of age. There was no difference in death or disability at age 5 years.

Together, these studies tell us that for most babies, moderate caffeine consumption (i.e. about 300 mg per day) by mom is unlikely to hurt a breastfeeding baby. However, these conclusions are limited by the small size of most of these studies. It’s too bad – and a little surprising – that we don’t have better data with which to advise women about one of the most common drugs used by breastfeeding moms.

Regardless of what the studies say, your most important data point is always your own baby. Your baby could be one of those with really slow caffeine metabolism and may be more sensitive to your caffeine intake. Since you’re unlikely to have the opportunity to measure your baby’s caffeine half-life (and probably wouldn’t want to, because this requires repeated blood draws), your best indicator is your baby’s behavior. If your baby is jittery or irritable and has trouble sleeping, then it might be worth trying to cut out caffeine for several days to see if this helps. Knowing that your baby’s caffeine metabolism will mature with age, you can try adding caffeine back into your life in a month or two. Of course, keep in mind that it’s also totally normal for an infant to be irritable and have trouble sleeping, with or without caffeine.

How much caffeine have you used while breastfeeding? Have you noticed that your baby is sensitive to your caffeine intake?

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