This story was originally published on August 22, 2019

It seems like every day we learn something new about how awesome breastmilk is. Did you know, for example, that breast milk "responds" to infections that your baby is exposed to? When your baby starts to develop an infection, such as the common cold, they will send antigens (pieces of the virus) into your breast. Your breast then acts as a pharmacy and makes antibodies to send back to your baby via breastmilk, which will help combat the virus.

Here's another one: Breastmilk ages with your baby! The breastmilk you provide your newborn with is different than the breastmilk you'll produce when they are 6 months old, and so on. Your body knows that your baby's needs change, so it adapts its milk to be as beneficial as possible for your baby's specific stage.

Mindblowing, huh?

Well in today's episode of breastmilk is magic: Breastmilk that is produced in the morning is different than breastmilk that is made at night.

Researchers have found that breastmilk pumped in the morning has significantly more cortisol in it than milk that's pumped at night. Cortisol is a hormone with a lot of responsibilities: It helps with metabolism, regulates blood sugar and supports memory. It also surges when we are stressed.

For all these reasons, cortisol is a good hormone to have onboard during the day. It makes sense that moms have more of it during waking hours, and therefore pass more of it on to their babies via breastmilk.

By the way, it does not appear that higher levels of cortisol in breastmilk relate to how much or how often babies cry. In other words, don't worry, mama: Your super-stressful day at work does not mean that your baby is destined for a night of crying.

That said, studies in monkeys have found that offspring that are routinely exposed to more cortisol in breastmilk may have more nervous and less confident dispositions as they grow up. Perhaps this is scientific support of taking that yoga class you've been thinking about.

On the flip side, research finds that breastmilk produced at night contains higher levels of melatonin, which is responsible for inducing sleep. And, you know how the tryptophan in turkey is said to cause our post-Thanksgiving fatigue? Well, nighttime breastmilk contains tryptophan, too.

So, how does this impact you and your baby?

If you are breastfeeding, it's simply a very cool thing to know. Your body is preparing your baby to be more or less ready for sleep, depending on what time of day it is.

If you are providing pumped milk to your baby, this information may impact how you do it.

Consider labeling not only the date you pumped each bag of milk but also the time. That 9 a.m. bag of breastmilk might not be the best choice for a just-before-bedtime feeding, as the higher levels of cortisol may keep them up. If you can, choose milk that was pumped later in the day or at night so the higher levels of melatonin can lull your baby into sweet slumber.

Like so much in motherhood, I would recommend using this advice as it works best for you and your family. If you are able to save melatonin-rich breastmilk for nighttime feedings, that's great. This may be particularly helpful information if you've been experiencing sleep struggles—it certainly can't hurt to try this approach and see if it helps!

But I wouldn't let it stress you out. Remember that every single time your baby gets breastmilk they benefit from it, regardless of what time of day it was pumped. So if these recommendations won't work for you, it's okay! Your baby will probably be just fine.

This is one more piece of evidence that you are incredible and that you are instinctively taking fantastic care of your baby.