Isn't it just the logical consequence of non-European immigration? AFAIK lactose intolerance is a pretty well-known phenomenon (unlike gluten): mamals are lactose intolerant after weaning, and as such most humans are so. There exist a few places (northern Europe, subsaharian Africa, southern? India, somewhere in the middle East) where the same kind of nonsense mutation on the gene responsible for weaning appeared, so people from there are usually lactose tolerant even after being weaned. The more people not coming from there there is in your population, the less lactose tolerant your population will be.
Edit: incorrect english wording
Unless you know for sure that you have the mutation, stopping drinking milk or consuming dairies at some point in your life comes with a risk of not being able to drink milk ever again in your life. (I don't mean that going vegan is bad or anything, but I wish people knew it can come with a bigger commitment that what you may expect)
What does this mean in the context you're using it?
Citation needed.
It's the most common allergen. Even in smallest amounts it's inflammatory even in those without obvious IgE allergy (tests for allergies are notoriously imprecise, even things like RAST and in-vitro lymphocyte stimulation).
1. Wikipedia: https://en.wikipedia.org/wiki/N-Glycolylneuraminic_acid#Effe...
2. MedCram: https://www.youtube.com/watch?v=xRkRilP1OTU
Is that not largely due to the change in ethnic composition? (And a fairly slight effect at that)
Good. It's remarkable how much cheese is included in restaurant meals. If you want to avoid it then it narrows the choice substantially.
Now this.