When Vitamin D Gets an F In Immunity

When Vitamin D Gets an F In Immunity

These days, visiting a health food store, online or in person, can feel like walking down the Las Vegas strip, what with all the glitzy claims and promises of miraculous health.   After all the flashy advertising, our patients have questions, even about old favorites like vitamin D.  We approach these questions calmly from a logical and evidential viewpoint, grading how much sense that supplement makes for that patient, whether it has some evidence to back up the claims, and whether it might have some risks behind the glitz.  With this in mind, this research article indicates that not all vitamin D is the same, and D2 might deserve a failing grade.

Since the advent of COVID in 2020, vitamin D has garnered more attention due to its immune supporting benefits.  Its bone boosting benefits were already widely appreciated by most providers and patients.  Beyond these benefits, the well-read know that this so-called vitamin acts more like a hormone in our cells and has several other benefits.  It supports the metabolism, lowers inflammation, and supports brain health among other bonuses.

From there, different questions arise, including how much and which form of vitamin D is the best.  Leaving the dosing question for another day, the D2 and D3 forms are the primary forms available.  Both have been used for decades, but this study suggests that at least when it comes to immune health, the D3 form outperforms its D2 relative.  Indeed, while the difference between the two is a minor molecular alteration, researchers found that supplementing with D2 appears to lower levels of the more active D3 form.

Noting that the D3 form is the one which better supports immune health, they recommend the D3 over the D2 form.  From their research, the D3 form better stimulates the type one interferon arm of our immune system.  This signaling arm plays an important role in defenses against viral and bacterial infections.

I am relieved to know that I have been correct in recommending vitamin D3 rather than D2 throughout my practice.  While some may like the idea of a plant based D2, the animal based D3 is superior, at least in respect to the immune system.   We therefore give D3 an A+ and D2 a failing F in the subject of immunity. Helping our patients at Sanctuary pursue healthier, more abundant lives requires our understanding the science, our application of that science to the patient sitting in front of us, and our work sharing our understanding so that more people can achieve that healthier life.  We hope this information helps you make a better-informed decision for your own family’s health.

Original Article:

Emily I G Brown, Andrea L Darling, Tracey M Robertson, Kathryn H Hart, Jie Li, Cathie Martin, Martin J Warren, Colin P Smith, Susan A Lanham-New, Ruan M Elliott. Effect of Vitamin D2 Supplementation on 25-Hydroxyvitamin D3 Status: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrition Reviews, 2025; DOI: 10.1093/nutrit/nuaf166

Thanks to Science Daily:

University of Surrey. “The vitamin D mistake weakening your immunity.” ScienceDaily. ScienceDaily, 4 October 2025. <www.sciencedaily.com/releases/2025/10/251004092911.htm>.

 

 

 

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Sanctuary Functional Medicine, under the direction of Dr Eric Potter, IFMCP MD, provides functional medicine services to Nashville, Middle Tennessee and beyond. We frequently treat patients from Kentucky, Alabama, Mississippi, Georgia, Ohio, Indiana, and more... offering the hope of healthier more abundant lives to those with chronic illness.