A couple of years ago I spent way too many hours in the sun at the height of summer in Barcelona. I browned nicely but never got sunburn. I assumed at the time it was somehow because of Vitamin D from the 'mega doses' of fish oil I'd been taking. (I was not keto at the time).
This summer I am keto (and stuck in northern England), but managed to get sunburn twice already I've calmed down on the fish oil, but I am supplementing with 5000IU Vitamin D most days (i.e. if I don't get much sun), so who knows.