I remember back in the 1980s that the Japanese researchers, whose population has (had?) very low cholesterol, were arguing with the US researchers, saying that

I remember back in the 1980s that the Japanese researchers, whose population has (had?) very low cholesterol, were arguing with the US researchers, saying that cholesterol too low was bad as it led to (perhaps allowed for) strokes- which was one of their young-people-killers.