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Myth check

Are two in five US adults really low on vitamin D?

It depends who reads the test. 41.6 percent of US adults counted as deficient at one cutoff, and the same blood result is deficient or fine depending on the guideline.

Vitamin D3 (Cholecalciferol)

Vitamin D deficiency comes with a striking number: 41.6 percent of US adults, from blood tests in 2005 and 2006. That count uses a line of 20 nanograms per millilitre, set for planning a population's needs, not for diagnosing anyone, and guidelines place it at 30, 20 or 12. The number describes a line someone drew as much as the people measured. Which line a result is read against decides whether someone is told they have a problem.

The findings behind this

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Other41.6 percent of US adults counted as deficient at one cutoff

Measured against 20 nanograms per millilitre, 41.6 percent of US adults counted as deficient, rising to 82.1 percent of Black adults. Move the line to 12 and the count falls.

★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.CautionThis is a snapshot of blood levels taken in 2005 and 2006, so it shows who sits below a line and never what being below it does to them. Race here stands in for skin pigmentation, sun exposure, diet and income all at once, rather than for anything measured biologically. Black Americans measure lowest without correspondingly worse bone density or fracture rates, which is the part the number does not explain.Click to keep this openProtect bones and jointsVitamin D3 (Cholecalciferol)
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OtherThe 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.

★☆☆Contested — the evidence disagrees with itself, or the finding carries a caution. A caution or conflict always shows one star, however strong the sources are.Conflicting evidenceThe 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.Click to keep this openProtect bones and jointsVitamin D3 (Cholecalciferol)

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