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

Test results that use terms like “normal” are reflecting values that are “within range” – meaning an acceptable range for optimal health. Anywhere within range is “fine”, though teetering on the edge of something doesn’t necessarily mean you’re going to suddenly drop dead. These determinations are made based on all the current data at a given time regarding optimal health, and therefore subject to change somewhat over time as science informs us. For example, blood pressure ranges were re-identified not so long ago to make anything over 120 systolic concerning on its own, whereas it used to not be a big deal if it were up to 130, as long as diastolic was under 80. Cholesterol types and ranges have also been modified. These numbers are not based on unhealthy population data however, but rather, what’s considered ideal for good health.

Edited to delete extra garbage and clarify.