Traditional teachings have included the idea that drinking is likely to optimise the yield of milk and in addition relax the mother and baby. With these ideas being so deeply held, towards the end to the 19th Century brewers produced a special beer for women lactating and sold it through drugstores. Even today similar beliefs exist in countries ranging from Germany to Mexico.

Scientific evidence has shown that breast fed infants consumed on average 20% less milk during the 2-3 hours after their mothers had taken an alcoholic beverage, as compared with occasions when the mother did not consume an alcoholic beverage. As milk production and intake very from one feeding to another the women were unaware of the difference. This variation may account of the erroneous belief that alcohol is an agent that promotes lactation.

The drop in the amount of milk consumed was as a result of a fall in milk production and this together with research on lactating rats, indicates that alcohol inhibits the release of hormones normally triggered by suckling, which stimulate the flow of milk. Some of the alcohol consumed by the lactating woman passes into her milk, where its concentration parallels that in her bloodstream.

Recent evidence indicates that the effects of alcohol in milk on suckling babies is that, it may impair the baby’s sleep, and heavy drinking has adverse effects on their development. One study showed that babies slept for a shorter period of time after their lactating mothers had drank lightly, compared with when the mother had consumed a non-alcoholic beverage.

"Unlike the situation during pregnancy, when alcohol consumed at any time is passed to the fetus, a lactating women can limit her infant’s exposure to alcohol by not nursing for several hours after drinking, until the alcohol has been eliminated from her milk" conclude the researchers.

Source.: Alcohol’s Effect on Lactation, Alcohol Research & Health (2001) 25, 230-234, Mennella J., Monell Chemical Senses Center, Philadelphia, PA, USA.