How do blood labs determine what is “normal”? Do they use average Americans who are obese and have diabetes and high blood pressure etc, or do they use “healthy” people?

Question

For example: Normal isn’t the same as optimal. Smoking used to be normal.

So if it says normal Vitamin D levels are 60 does that mean it’s the optimal level or just what level is common?

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Answer 1

When they say “normal” it’s the level where they don’t see adverse effects, not just the median of all people 🙂