Cheese and butter go back a long way as methods of preserving milk. But fresh milk was considered baby food, or a boost for growing children, through most of history. Only about a hundred years ago did milk drinking become common among adults. That was because of the convergence of several trends around the beginning of the 20th century. First, the milk trade became regulated and safer (see our previous articles on that development). Then there was the craze for healing through nutrition, which led to the development of cereals, served with milk (see our previous article on that). And there was the Temperance movement, with groups trying to get men to drink anything besides alcohol (which we also covered). Read more about these trends and how they led to people rushing out to buy milk before a snowstorm hits, at BBC Future. -via mental_floss
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There may have been a dip in milk consumption at the start of urbanization, when increasing numbers of people couldn't get fresh milk locally, but their claim is much more sweeping and ridiculous than that... There were some periods in western history where adults mostly drank alcoholic beverages (small beer, wine, grog, etc.), before we discovered other ways to make polluted water safe to drink, but that has nothing specifically to do with milk.
* https://en.wikipedia.org/wiki/Milk#Industrialization
* http://www.livescience.com/37649-why-people-drink-milk-benefits.html