Dietary genes aren’t correlated to race of course, except for rare ones like Inuits adapting to eating more fat.
For a large scale study I would check if they correlated for geography, blood markers and diet outside the supplements.
Hell, look at the distribution of lactose intolerance. Is drinking milk racist?
Actually, the most lactose intolerant people I know are totally white and I think actually have worse undiagnosed medical problems but just think they’re lactose intolerant. And Asians I know aren’t lactose intolerant because even though they “are Asian” culturally and would look Asian to you they’re actually 2/3 genetically Scottish.
Testing milk as a supplement would be interesting I guess; I know in the 90s we were all taught it was needed for bones but more recently this is said to not be true because 1. bones need vitamin K which we don’t get enough of and 2. cows milk contains galactose which is bad for bones and may cause osteoporosis.