A vitamin D result of 25 ng/mL is sufficient under one standard and insufficient under another. Both standards were set by major expert bodies, using largely the same evidence.
Understanding why they differ explains more than the number itself does.
Two thresholds, one evidence base
The two positions are well documented because the bodies holding them published a direct exchange.
The Endocrine Society defines sufficiency as above 30 ng/mL, insufficiency as 12–30 ng/mL, and deficiency as below 12 ng/mL[1].
The Institute of Medicine set 20 ng/mL as the level meeting the requirements of most people.
In 2012, IOM committee members published a response to the Endocrine Society guideline listing three explicit disagreements[2]:
- They disagree that 25(OH)D levels of 30 ng/mL or higher provide increased health benefits compared with 20 ng/mL
- They disagree that all persons are deficient below 20 ng/mL
- They argue the guideline incorrectly characterises several large subgroups as at risk
Their conclusion was pointed: with no evidence for benefit, it is difficult to justify the billions in health care dollars that widespread screening would require[2].
That’s an unusually direct disagreement between expert bodies, and it hasn’t been resolved.
Why they diverge
The two documents were written for different purposes, which explains much of the gap.
The IOM figure is a dietary reference intake — a population-level standard, answering “what level meets the requirements of most healthy people?”
The Endocrine Society figure is a clinical guideline — answering “what level should a clinician aim for in a patient being treated?”
A population reference and a treatment target are different quantities. Neither body was answering the other’s question, which is part of why the same evidence supported both.
International practice reflects the split. Australia and New Zealand treat ≥20 ng/mL as sufficient. Switzerland does the same[3].
What the cutoff does to a population
This is where the abstract disagreement becomes concrete.
A Korean study measured 25(OH)D in 180,289 subjects and calculated deficiency prevalence at every commonly used threshold[3].
| Threshold | Below it |
| < 5 ng/mL | 0.4% |
| < 10 ng/mL | 12.5% |
| < 12 ng/mL | 20.6% |
| < 20 ng/mL | 49.4% |
| < 30 ng/mL | 75.3% |
[Table 1] Prevalence by threshold, same population · Source: Domestic studies involving 180,289 participants[3]
Half the population or three-quarters, depending on which line is drawn. Same blood samples, same measurements.
That’s the practical weight of a definitional choice. It determines whether a country describes itself as having a widespread deficiency problem or a moderate one.
One counterintuitive detail from the same study: prevalence below 30 ng/mL was higher in younger participants (79.6–85.5% in their 20s–40s) than older ones (62.6–69.2% at 50 and above)[3].
Korea’s official position, and what clinics use
Here’s the finding most relevant to readers here.
In Korea, ≥20 ng/mL is regarded as the appropriate concentration for skeletal health by the Ministry of Health and Welfare and by the physicians’ guidelines for osteoporosis[3].
Korea’s official standard is 20.
But the same paper notes what happens in practice: values below 10 for deficiency and below 30 for insufficiency — the Endocrine Society thresholds — are commonly used in local clinics and hospitals in Korea[3].
So a result can be reported as insufficient against a standard that isn’t the national one.
This isn’t a criticism of clinicians. Laboratory reference ranges come from assay manufacturers and international guidelines, and a clinician interpreting a result alongside a patient’s full picture is doing something more nuanced than applying a line.
But it does mean the reference range printed beside a result may not reflect the national standard — which is worth knowing before drawing conclusions from where a number falls.
KNHANES data shows what the choice implies. Below 20 ng/mL: 47.3% of Korean men and 64.5% of women. Above 30 ng/mL: 13.2% of men and 6.7% of women[4].
Under the 30 ng/mL standard, roughly 93% of Korean women would be classified as below sufficiency.
A definition that classifies the overwhelming majority of a population as abnormal is worth examining rather than accepting — which is precisely the IOM’s objection.
Korea isn’t alone in raising it. Researchers in Poland published a study asking directly whether the 30 ng/mL cutoff is suitable for their population[5]. The question is being asked in several countries.
What a number can and can’t settle
Three things follow, and none of them involve interpreting your own result.
A single threshold isn’t a fact about biology. It’s a decision about where to draw a line on a continuous distribution, made for a stated purpose. As covered in the upper intake post, the same is true of the other end of the range.
Context determines meaning more than the number does. Calcium intake, bone density, fracture history, medication, season of testing, and body composition all bear on what a given level implies — which is why interpretation belongs with someone who has that information.
And a result near a threshold is the least informative kind. Assay variation between laboratories is a recognised issue in this field, so a value close to a cutoff may sit on the other side when repeated.
The relevant question this series keeps arriving at applies here too: as covered in the VITAL post, supplementation showed no fracture benefit in a population whose mean baseline was 30.7 ng/mL — already above both thresholds. The evidence that supports correcting a genuine shortfall does not extend to raising an adequate level higher.
For readers moving between countries
Two practical notes.
Units differ. Korea and the US report ng/mL; much of Europe reports nmol/L. The conversion is 1 ng/mL = 2.5 nmol/L, so 20 ng/mL is 50 nmol/L and 30 ng/mL is 75 nmol/L. A result of “50” means very different things in the two systems.
And the standard applied to you may change with your address, without anything about you changing. A result classified as sufficient in Sydney or Zurich may be reported as insufficient in a Seoul clinic using Endocrine Society ranges. As covered in the DXA T-score post, this pattern recurs across biomarkers — the same measurement meeting different reference standards.
Vitamin D is not part of Korea’s national health screening panel, as covered in the screening post, so testing here generally follows a specific clinical question rather than routine practice.
Closing
The disagreement here isn’t about measurement. Both bodies looked at the same evidence and drew the line differently because they were answering different questions — one about population requirements, one about clinical targets.
What makes it worth understanding is the consequence. In one Korean dataset of 180,289 people, moving the line from 20 to 30 ng/mL took deficiency prevalence from 49.4% to 75.3%. Under the higher standard, about 93% of Korean women would fall short.
Korea’s official position is 20 ng/mL. Many Korean clinics use 30.
So the honest reading of a vitamin D result is that it locates you on a distribution — and where the line falls on that distribution is a judgement call with an ongoing dispute behind it.
Which is an argument for discussing the number with someone who knows your situation, rather than comparing it to whichever threshold you find first.
Key Terms
- 25(OH)D — the circulating form of vitamin D measured to assess status.
- ng/mL and nmol/L — the two reporting units; 1 ng/mL = 2.5 nmol/L.
- Dietary reference intake — a population-level standard for meeting the requirements of most healthy people.
- Clinical guideline — recommendations for managing individual patients, a different purpose from a population reference.
- Reference range — the range printed alongside a laboratory result, set by the laboratory or assay manufacturer.
- Assay variation — differences in results between laboratories using different measurement methods.
At a Glance
- Endocrine Society: sufficiency above 30 ng/mL. Institute of Medicine: 20 ng/mL meets most people’s requirements
- IOM members published three explicit disagreements, including that 30 provides no added benefit over 20
- The gap reflects purpose — a population reference versus a clinical target
- Australia, New Zealand and Switzerland treat ≥20 ng/mL as sufficient
- In 180,289 Korean subjects, deficiency prevalence was 4% below 20 ng/mL and 75.3% below 30
- Korea’s official standard is ≥20 ng/mL (Ministry of Health and Welfare and osteoporosis guidelines)
- But Endocrine Society thresholds are commonly used in Korean clinics
- KNHANES: only 7% of Korean women exceed 30 ng/mL — the higher standard would classify ~93% as below sufficiency
※ This article explains why reference thresholds differ and is for general information only. It is not a guide to interpreting your own result and does not support self-diagnosis. Laboratory values must be interpreted alongside individual clinical context by a qualified clinician. Do not begin, stop or adjust vitamin D supplementation on the basis of a number without medical advice — vitamin D is fat-soluble and accumulates.
References
- “Vitamin D Deficiency”, StatPearls, NCBI Bookshelf (2019 Endocrine Society sufficiency, insufficiency and deficiency definitions), https://www.ncbi.nlm.nih.gov/books/NBK532266/
- Rosen CJ, Abrams SA, Aloia JF, et al. “IOM Committee Members Respond to Endocrine Society Vitamin D Guideline”, Journal of Clinical Endocrinology & Metabolism (three points of disagreement; screening cost objection), https://pmc.ncbi.nlm.nih.gov/articles/PMC5393439/
- “Recent Information on Vitamin D Deficiency in an Adult Korean Population Visiting Local Clinics and Hospitals”, Nutrients 2022;14(9):1978 (180,289 subjects; prevalence by threshold; Korean official standard versus clinic practice; international comparisons), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9101007/
- “The Prevalence of Vitamin D Deficiency among Cancer Survivors in a Nationwide Survey of the Korean Population”, PMC (KNHANES figures by sex above and below thresholds), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4457839/
- “Effect of Summer Sunshine Exposure on Vitamin D Status: Is 30 ng/mL Really Suitable for the Polish Population?”, PMC (parallel examination of threshold suitability in another national population), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8345518/