If you’ve made it this far in the series, you might be wondering:
Why were the 2011 Endocrine Society guidelines so confident in higher vitamin D thresholds, despite limited supporting evidence?
One possible piece of the puzzle is conflicts of interest.
If you haven’t read the previous posts in the series check out:
- Part 1: The Vitamin D Controversy
- Part 2: Vitamin D Beyond Bone Health (Part 2): What Do We Really Know?
- Part 3:The Vitamin D Controversy (Part 3): What Changed in 2024?
Conflicts of interest in guideline development
In 2018, the Endocrine Society published an analysis examining financial conflicts of interest among authors of their clinical practice guidelines.
They found that:
- Only some of the National Academy of Medicine’s recommended best practices were being followed
- There was room for improvement in how conflicts of interest were managed
This doesn’t invalidate the guidelines—but it does highlight the importance of transparency and critical appraisal.
A closer look at industry relationships
One of the most frequently cited authors in the vitamin D literature—and a key figure in the 2011 guidelines—is Dr. Michael Holick.
His 2011 disclosure statement included relationships with multiple organizations, including:
- Pharmaceutical companies
- Diagnostic companies
- Industry groups related to vitamin D–containing products
One relationship that has received particular attention is with Quest Diagnostics, a company that does vitamin D testing.
According to reporting from The New York Times (also summarized by KFF Health News), Dr. Holick earned substantial income through industry partnerships, including those connected to vitamin D testing.
Why does this matter?
When experts who shape clinical guidelines have financial relationships with industries that may benefit from:
- Increased testing
- Expanded definitions of deficiency
- Higher supplementation targets
…it raises important questions about how recommendations are formed.
Again, this doesn’t mean the science is wrong—but it does reinforce the need to:
- Evaluate the quality of evidence
- Consider potential sources of bias
- Avoid relying on a single guideline without context
The cost of getting it wrong
At a systems level, these recommendations can have significant consequences.
For example:
- In 2014, U.S. insurers reportedly spent $33 million on vitamin D testing alone
That’s a substantial investment—particularly given that:
- Routine testing is no longer recommended for most populations
- The 2011 thresholds have been retracted
Retracted research
Another issue within the vitamin D literature is the presence of retracted studies.
Retracted papers are removed from the scientific record due to major concerns, such as:
- Methodological flaws
- Data issues
- Incorrect conclusions
One example includes a paper on vitamin D and COVID-19 authored by Dr. Holick, which was later retracted after concerns were raised by the scientific community.
While retractions are part of how science self-corrects, they also highlight the importance of:
- Ongoing scrutiny
- Not over-relying on emerging or low-quality evidence
Key takeaways
- Financial conflicts of interest are common in guideline development and need to be carefully managed
- They do not automatically invalidate recommendations—but they should prompt critical appraisal
- The vitamin D story highlights how:
- Weak evidenceStrong recommendationsAnd potential bias
Final thoughts
It’s hard to ignore the possibility that financial incentives can influence how evidence is interpreted and communicated—especially when recommendations affect large populations.
As clinicians, this is a good reminder to:
- Look closely at how evidence is used, not just the conclusions
- Pay attention to which thresholds are being applied
- Stay open to updating practice as better evidence emerges
Vitamin D is a great case study in how science evolves—and how important it is to approach guidelines with both curiosity and a healthy degree of skepticism.
