Do Nursing and Drinking Mix?

Medical science admitted some years ago what most Europeans would have told you all along: While heavy alcohol consumption is seriously dangerous for a developing baby, it's okay for a pregnant mother to have a little bit of wine or beer once in a while. However, it seems all pregnant mothers have at least one story of a bystander saying, "You're drinking? But that can't be good for the baby!"

Nor does the helpful advice stop when baby is safely born. Nursing mothers are also often warned that it can't be good for baby to get "all that alcohol" in mommy's breast milk. Books and articles tend to take the "better safe than sorry" line as well. Advice website Baby Center answers the question thus:

Will it harm my breastfeeding baby if I drink wine, beer, or hard alcohol?

It could if you don't take precautions. The same amount of alcohol that makes it into your bloodstream makes it into your breast milk.

While the amount that's transferred if you drink a glass of wine is relatively small, your baby is tiny and has an immature liver. That means she can't process the alcohol as well as you can. Infants younger than 3 months process alcohol at about half the rate of adults.
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While no one knows the true effect that alcohol has on breastfed infants, it's probably wise to abstain – at least in the very beginning. Some experts recommend breastfeeding moms avoid drinking alcohol until their baby is 3 months old.

How can I safely have an occasional drink?

Wait at least two hours after you finish a drink before nursing your baby to give your body a chance to clear the alcohol.
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You can time your drink so that your baby won't be nursing for a few hours afterward by having it right after a feeding, for example, or during one of your baby's longer stretches of sleep.

Or you can pump and store your milk before having a drink, then feed your baby expressed milk from a bottle. (Pumping after you drink won't clear alcohol from your system any faster – it will still take at least two hours.)

Another option is to feed your baby formula in the hours following your alcohol consumption.

Pretty serious stuff, eh?

This sounded wrong to me, especially given that they start off by saying "The same amount of alcohol that makes it into your bloodstream makes it into your breast milk."

Alcohol does indeed get absorbed into the bloodstream relatively quickly after you drink it. It then circulates with the blood until the liver metabolizes it, something the liver does at the rate of 0.015 of blood alcohol concentration every hour. However, there's a lot of blood in the human body, and so the alcohol that you drink quickly gets diluted to a much lower level -- aside from the fact that even as it's being absorbed into the blood the liver is already metabolizing it out.

A common legal definition of intoxication is 0.08% blood alcohol concentration. By comparison, the concentration of alcohol in wine is often around 12%. In other words, the concentration of alcohol in wine is 150 times higher than is the concentration of alcohol in the blood in an intoxicated person. So saying that breast milk absorbs alcohol at the same rate as blood, and thus that your "milk alcohol concentration" is the same as your blood alcohol concentration, is not actually saying all that much. Compared to any kind of drink, blood alcohol concentration is just not that high.

Still, babies are small, and at least some sources say that they metabolize alcohol only half as fast as adults, so perhaps the small amount of alcohol has an outsize effect. Let's run the numbers.

Blood alcohol concentration can be estimated using a formula called Widmark's Equation after the Swedish physician who developed it. The formula is:

([constant for body water in blood = 0.806] x [number of standard drinks containing 10 grams of ethanol] x [factor converting grams to Swedish standards used for calc = 1.2]) / ([body water constant = 0.49 for women][body weight in kg]) - (metabolism rate = 0.017 for women) x (drinking period in hours)

I've assumed a very small mother (130lb) who drinks two 5oz glasses of wine in one hour. This puts her at 0.08% BAC, right at the legal definition of intoxication -- she should not drive. Now, mommy sits down to nurse her new baby. I've assumed a very tiny baby at 8lbs. I've also cut the rate of metabolization by half per the mentions of babies metabolizing more slowly.

Baby consumes 5oz of Mommy's milk, which now as an alcohol content of 0.08%. I ran the same equation for baby and got a negative number. Why? Because the tiny quantity of alcohol (the same amount that is in one fifth of a teaspoon of wine) would be metabolized by the baby in less than the hour it would take to get fully into the blood stream. If we take away the effect of metabolization, we get a blood alcohol level for baby of 0.005%

Looked at another way, the effect that drinking the milk of Mommy (who as a light weight who's slammed two full glasses of wine in one hour is now legally intoxicated) would have on baby is the same as the effect that drinking one half ounce of wine would have on a 130lb woman.

In other words, if Mommy is drinking moderately, there should be no discernible effect upon her nursing baby.

Translation: Beer is nourishing.  This one drinks it.  That one doesn't drink any.

UPDATE: A friend provided this link where a mother takes an empirical approach, measuring the alcohol content of breast milk after drinking varying amounts of alcohol.