The same blood result is deficient or fine, depending who reads it
The Endocrine Society calls anything below 30 nanograms per millilitre deficient. The National Institutes of Health uses 20, and some bodies use 12.
What the study found
No two authorities agree where deficiency begins
The Endocrine Society calls anything below 30 nanograms per millilitre of 25-hydroxyvitamin D deficient. The National Institutes of Health uses 20, and some bodies use 12. The US Preventive Services Task Force says no single cut point defines it, because requirements differ between people.
The caveat · Set for populations, not one person
The 20 nanogram figure was set as a population planning number covering the needs of nearly everyone, not as a line for diagnosing one person, and the committee that set it has said so in print. The Institute of Medicine derived it from bone health alone, having found the evidence on cancer, heart disease, diabetes and infection too thin to set requirements on. Which number a person is measured against decides whether they are told they have a problem.
What we don't know
Where vitamin D deficiency begins is unsettled: expert lines sit at 30, 20 and 12 nanograms per millilitre. Evidence cannot choose between them, because no trial has tested whether measuring a level and acting on it does anyone good.