Is caffeine keeping my newborn awake?

2025-05-23

My wife and I have a six-week old baby boy, who, unsurprisingly, is going through a period where it is harder and harder to get him to sleep for a nap. My wife was pouring a cup of coffee, and I remarked, I wonder if caffeine is passed through breastmilk? Seems like something that would be good to be aware of.

As it turns out, "caffeine appears rapidly in breastmilk after maternal ingestion"! This is not to say that it is unsafe to take caffeine while breastfeeding. Many online resources tell us that it is safe. From the first few results on Google:

• "The news is good: while caffeine does pass into breastmilk, breastfed babies generally do not suffer ill effects from moderate caffeine consumption through breastmilk." source
• "The short answer is yes, it is generally safe to drink caffeine while you are breastfeeding your baby." source
• "Most breastfeeding mums can drink a moderate amount of caffeine (eg a few cups of coffee or tea each day) without it affecting their babies." source

But does a newborn receive enough caffeine through breastmilk that it might affect their sleep? A 1985 study measured the caffeine concentrations in breastmilk and in infant blood serum. After 5 days of 750mg/day of caffeine, the average concentration in infant serum was 1.5 micrograms/ml, which is approximately the level at which it starts to affect sleep patterns in adults. Now, 750mg/day is almost a two-liter bottle of black coffee, what I would consider a titanic amount for one day. And

A followup study by the same author failed to detect an effect on infant sleep time of 500mg/day of caffeine. However, the sleep study only had a sample size of 11. The dosed 500mg/day of caffeine is well above the level that would impact most people's sleep if they took it right before bed, but the study failed to detect an impact on sleep time even in the mothers. So there's some reason to doubt that the variables measured here really capture the impact that caffeine might potentially have on a newborn.

Unfortunately, I don't believe any study like this can come close to answering the ten-thousand dollar question for me right now: "does caffeine consumption make it harder to put your newborn down for a nap?" Our son's "sleep time" variable from today is the sum of probably a dozen naps of at most 10 minutes each. If he's got his eyes closed but is furiously sucking on his pacifier, does that count as sleep? There are a million factors that affect whether any given calming attempt is going to result in a decent hour-long sleep. When I read that caffeine hasn't been found to have a measurable impact... well, "measurable" is doing all of the work in that sentence.