Did you know that the threshold for diagnosing a vitamin D deficiency is highly controversial?
I didn’t—until I listened to an episode from one of my favourite podcasts:
https://www.normalcurves.com/vitamin-d-part-1-is-the-deficiency-epidemic-real/
Even though I first heard this episode quite some time ago, the topic of vitamin D keeps coming up in practice. So I decided to take a deeper dive—and turn it into a blog series.
Who sets the guidelines?
Two major groups have shaped how we think about vitamin D:
- The Institute of Medicine (IOM) Committee on Dietary Reference Intakes
- The Endocrine Society Task Force
This series is informed by several key papers (listed below), including perspectives from both sides of the debate.
- Rosen, Clifford J., et al. “IOM committee members respond to Endocrine Society vitamin D guideline.” The Journal of Clinical Endocrinology & Metabolism 97.4 (2012): 1146-1152.
- Vieth, Reinhold, and Michael F. Holick. “The IOM—endocrine society controversy on recommended vitamin D targets: in support of the endocrine society position.” Vitamin D. Academic Press, 2018. 1091-1107.
- Irwig, Michael S., Mabel Kyinn, and Mason C. Shefa. “Financial conflicts of interest among authors of Endocrine Society clinical practice guidelines.” The Journal of Clinical Endocrinology & Metabolism 103.12 (2018): 4333-4338.
- Bouillon, Roger, and Cliff Rosen. “The IOM–Endocrine Society controversy on recommended vitamin D targets: in support of the IOM position.” Vitamin D. Academic Press, 2018. 1065-1089.
- McCartney, Christopher R., et al. “Vitamin D insufficiency and epistemic humility: an endocrine society guideline communication.” The Journal of Clinical Endocrinology & Metabolism 109.8 (2024): 1948-1954.
- Demay, Marie B., et al. “Vitamin D for the prevention of disease: an endocrine society clinical practice guideline.” The Journal of Clinical Endocrinology & Metabolism 109.8 (2024): 1907-1947
How the controversy began (2011)
In early 2011, the IOM released updated Dietary Reference Intakes (DRIs) for calcium and vitamin D. They recommended defining vitamin D deficiency as:
- <20 ng/mL (50nmol/L)
Later that year, the Endocrine Society published its Clinical Practice Guideline, recommending a higher threshold:
- <30 ng/mL (75nmol/L)
This difference sparked a long-standing controversy that continues to influence practice today.
Where the guidelines agree—and disagree
Areas of agreement:
- Vitamin D is essential for skeletal health
- There is limited evidence for benefits beyond bone health (e.g., cardiovascular disease, mortality, quality of life)
- Routine screening of the general population is not recommended
Key disagreements:
- Optimal serum levels:
- IOM: benefits above ~20 ng/mL (50nmol/L)
- Endocrine Society: benefits above ~30 ng/mL (75nmol/L)
- Definition of deficiency:
- IOM: <20 ng/mL
- Endocrine Society: <20 ng/mL (deficiency), 20–30 ng/mL (insufficiency), >30 ng/mL (sufficient)
- Who requires higher levels:
- IOM: No strong evidence for higher targets in specific groups
- Endocrine Society: Higher levels recommended for conditions such as osteoporosis, CKD, malabsorption, obesity, and pregnancy
Why did the IOM choose 20 ng/mL (50nmol/L)?
The IOM based their recommendations primarily on bone health outcomes, including:
- Calcium absorption
- Bone mineral density
- Osteomalacia and rickets
They concluded that maximal skeletal benefit occurs around 12–16 ng/mL, and therefore set a conservative deficiency threshold at 20 ng/mL.
For the general population, they estimated:
- ~50% achieve adequacy at 16 ng/mL (40nmol/L)
- ~97.5% achieve adequacy at 20 ng/mL (50nmol/L)
They also concluded that:
- 400–800 IU/day is sufficient for most people
Importantly, their recommendations were designed for the general healthy population, not high-risk clinical groups.
Why did the Endocrine Society choose 30 ng/mL (75nmol/L)?
The Endocrine Society based their higher threshold on three main considerations:
- Parathyroid hormone (PTH): Lower levels may occur when vitamin D >30 ng/mL
- Falls: Reduced risk suggested above 30 ng/mL
- Calcium absorption: Potentially higher at levels >30 ng/mL
The IOM’s counterarguments
1. Parathyroid hormone (PTH)
The IOM found inconsistent evidence linking vitamin D levels to optimal PTH suppression. They also raised concerns about the quality and interpretation of studies used by the Endocrine Society, including:
- Weak correlations (e.g., r = 0.04)
- Interpretation Note: When looking at correlations remember that 1 or -1 means a very strong correlation and 0 means almost no correlation, so a value of 0.04 is very weak.
- Methodological limitations
- Use of populations on medications affecting PTH (e.g., bisphosphonates)
2. Falls in older adults
The Endocrine Society relied on a 2009 meta-analysis. The IOM identified several issues:
- Poor reporting of methods
- Misleading data presentation
- Selective analyses
After re-analyzing the data, the IOM found no significant reduction in falls (p = 0.17).
3. Calcium absorption
The IOM criticized reliance on a small study (n=34) while larger studies (n≈1300) suggested:
- Maximal calcium absorption may occur at much lower levels (as low as ~8 ng/mL)
Who is “at risk”?
The IOM also challenged who should be considered “high risk.”
Dark-skinned populations
Because recommendations assumed minimal sun exposure, the IOM considered these individuals part of the general population.
Pregnancy and lactation
- No strong evidence that higher vitamin D levels improve outcomes
- High-dose supplementation (4000–6400 IU/day) increases breast milk vitamin D—but exceeds recommended upper limits
Older adults with fractures
- Vitamin D alone has limited impact
- Vitamin D + calcium shows benefit for fracture reduction
People living with obesity
- Lower serum vitamin D may reflect sequestration in adipose tissue
- Levels often rise with weight loss (without increased intake)
- No clear evidence that higher supplementation improves outcomes
Key takeaways
This post introduces a controversy that began in 2011 and continues to shape clinical practice.
From the IOM perspective:
- There is limited evidence of benefit for 25(OH)D levels above ~20 ng/mL (50nmol/L)
- These recommendations apply broadly to the general population
- The evidence supporting higher targets has important limitations
Your turn
What reference range does your lab use?
Does it align with the IOM or the Endocrine Society?
Take a look before continuing—you might be surprised.
Up next
Part 2: The Vitamin D Controversy—The Intervening Years
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