30 years ago when my oldest was a baby....both pediatricians and ob's would tell nursing mothers to have a beer or a glass of wine around 4-6pm, as it would help increase milk production. It was thought that it would relax the mother, gets some sugar (calories) and liquids into the mother which have depleted during the day, and also to help the baby "settle" and sleep better at night so the mother is able to get some rest.
I rather doubt they tell nursing mothers to do that any more.