Look, this is not to say that it is invalid, far from it. It’s just that I think you have to be a lot more careful. It could be that Japanese vs Japanese Americans is one of those Apples vs Oranges comparisons. Are Japanese Americans really like Japanese?
Genetically yes, Japanese Americans are like Japanese [1]. Their diets are also closer to Japanese diets than standard American diets.
I may only be comparing lemons to oranges, which I agree is only marginally better than apples to oranges. But that's ok - I'm certainly NOT trying to make the claim that US health care is better than Japanese health care as a result [2]. I'm simply pointing out that if you include slightly better controls, the effect completely reverses itself. This strongly suggests the original comparison is crappy.
[1] Genes matter. A fact I've heard - Indians have narrower blood vessels than non-Indian Whites, leading them to be more vulnerable to hypertension. The UK NHS takes this into account when giving medical advice, though supposedly US doctors do not (that would be racist).
[2] To draw conclusions like that, you need to take groups of statistically similar people with the same disease and measure health outcomes. No one does this, it's very hard.
Look, this is not to say that it is invalid, far from it. It’s just that I think you have to be a lot more careful. It could be that Japanese vs Japanese Americans is one of those Apples vs Oranges comparisons. Are Japanese Americans really like Japanese?