A groundbreaking study reveals that millions of Americans taking vitamin D2 supplements are unknowingly sabotaging their immune systems by lowering crucial D3 levels in their bodies.

Story Highlights

• New UK research shows vitamin D2 supplements actively decrease beneficial D3 levels
• D3 is essential for immune defense against viruses and bacteria, while D2 undermines this protection
• Study challenges decades of public health guidance treating D2 and D3 as interchangeable
• Consumers, especially vegans using plant-based D2, may need to reconsider supplement choices

Researchers Expose Hidden Vitamin D Danger

A comprehensive meta-analysis by UK researchers from the University of Surrey, John Innes Centre, and Quadram Institute Bioscience has uncovered a previously unknown risk in vitamin D supplementation. Published in Nutrition Reviews in October 2025, the study analyzed 11 randomized controlled trials spanning from 1975 to 2023, revealing that vitamin D2 supplements can actually decrease the body’s levels of vitamin D3. Lead researcher Emily Brown stated that this represents “a previously unknown effect” that undermines the intended health benefits of supplementation.

The findings directly contradict longstanding assumptions in public health guidance. For decades, government agencies and healthcare providers have treated vitamin D2 and D3 as essentially equivalent options for addressing deficiency. The UK government currently recommends 10 micrograms of vitamin D daily during winter months, without distinguishing between forms. This new evidence suggests such guidance may need immediate revision to protect public health and ensure Americans get proper immune system support.

🧠 Are You Making This Vitamin D Mistake That Could Be Weakening Your Immunity?

Recent research highlights an important distinction between vitamin D2 and vitamin D3, one that could have a significant impact on your immune health.

While both forms are often labeled simply as… pic.twitter.com/Sw1xOUVPKA

— GrassrootsHealth (@Grassroots4VitD) October 9, 2025

Immune System Compromise Threatens Health Defense

Professor Colin Smith’s research team discovered that vitamin D3, but not D2, stimulates the type I interferon signaling system—a critical component of immune defense that provides the first line of protection against bacteria and viruses. This means Americans taking D2 supplements are not only missing out on immune benefits but actively suppressing their body’s natural defense mechanisms. The implications are particularly concerning given ongoing health challenges and the importance of maintaining robust immune function.

The study’s revelation that D2 can lower D3 levels represents a serious breach of consumer trust in supplement efficacy. Many Americans, especially those following plant-based diets, have chosen D2 specifically because it’s derived from plants rather than animal sources. Professor Cathie Martin acknowledged this concern, emphasizing the urgent need for plant-based D3 options to ensure vegans and vegetarians aren’t disadvantaged by their ethical dietary choices.

Watch: This Vitamin D Mistake Is Making You Sicker (Do This Instead)

Industry Overhaul and Consumer Protection Needed

The research exposes significant gaps in supplement regulation and labeling that have left consumers vulnerable to making uninformed choices. Moving forward, supplement manufacturers face pressure to reformulate products and update labeling to reflect these critical differences. The findings demand immediate action from regulatory agencies to ensure proper consumer protection without government overreach. Americans deserve transparent, accurate information about supplement effects so they can exercise personal responsibility in health choices. The study’s authors recommend that most individuals choose D3 supplements, subject to personal considerations, to optimize health benefits and immune system function.

Sources:

How Taking the Wrong Vitamin D Supplement Can Harm Your Immune System
Scientists Warn Common Vitamin D Supplement Has Previously Unknown Negative Effect
Vitamin D: Are You Taking the Right Type of Supplement? Study Says the Wrong One Can Actually Affect Your Immunity
Scientists Warn Common Vitamin D Supplement Has Previously Unknown Negative Effect