Ansel Keys observed a stark difference in cardiovascular disease risk between those with cholesterol < 100 mg/dL and those with cholesterol > 200 mg/dL in the 1950s.

“if we go back into the 1950s ansel keyes was potentially one of the first people to utilize the then nascent assay for measuring total plasma cholesterol so to your point earlier that number let's say you measure 200 milligrams per deciliter that's simply telling you that that's the sum total of cholesterol in all of the lipoproteins and what ansel keys and others observed and this was by now we're probably into 1957 1958 was hey if you stratify people at the bottom five percent and people at the top five percent so that might be people whose total cholesterol is less than maybe a hundred milligrams per deciliter and people whose total cholesterol is more than 200 milligrams per deciliter there's a stark difference in their mortality or rather in their risk of cardiovascular disease”