No readings, but it's mostly white people that have the genes for lactase in adulthood, the enzyme that breaks down lactose. It's not just whites, of course, it's also prevalent in other regions that breed cows like South Sudan. But it's almost unheard of in Native Americans, very rare among East Asians, and not very common among Africans. There are also degrees of it, I can drink as much milk as I want to, other people are fine with a cup, my mom cannot drink half a cup without getting sick.
And yes, that's the reason why the alt-right uses the milk thing.