> And, now you've discovered why Europeans have light skin [1]! And, why supplementation is suggested for those with dark skin [2] living in regions with light skinned natives!
What does the color of skin have to do with the normal amount of a vitamin in blood?
Skin tone merely regulates how much you end up producing. Just because your skin is bright doesn't mean you need less of a vitamin.
I'm sure there is some variance in this, but I doubt it's swinging between 20 and 30 ng/mL
Because vitamin d is produced by sun. Light skin means less sun is required. I suggest a cursory look into vitamin d production [1], to more align your perspective to accepted science.
Are you kidding? The discussion is explicitly about the normal levels. How much you produce is irrelevant. The _level_. As in how much of it is floating in your blood.
Some levels are normal, some are low. "Skin color" affects production as you pointed out, but that has literally nothing to do with what we are discussing.
It's not some "your bones fall apart if you're low". It's just like literally every other nutrition related thing. You can have too little or too much. Bad things increase the more you go towards either direction.
For knowing how much blood level is "good", if you go back [1], that's why I suggested a good starting point would be looking at any native with an average pre civilization type days worth of outdoor activity and attire. For example, native African in their sunny climate, native European in their cloudy climate, etc. You probably also have to look at their pre-civilization diets, if they were too different from the average today (like traditional Inuit diet).
And, as I said, if there's no difference to be expected in baseline "healthy" vitamin D levels across genetic populations (a native African or native European), you could just go same some people in Africa or Papa New Guinea, right now, where you can find some populations living (at least very close to) pre-civilization lives, and measure theirs for some reasonable ground truth.
What does the color of skin have to do with the normal amount of a vitamin in blood?
Skin tone merely regulates how much you end up producing. Just because your skin is bright doesn't mean you need less of a vitamin.
I'm sure there is some variance in this, but I doubt it's swinging between 20 and 30 ng/mL