With a multitude of health benefits, vitamin D plays a vital role in every aspect of human health, including immune support.

There are two forms, but they aren't created equal.

• Vitamin D2 (ergocalciferol), which comes from vegan sources such as mushrooms.
• Vitamin D3 (cholecalciferol) comes from algae and animal sources. D3 is also manufactured by the body in response to sunlight (hence its moniker, "the sunshine vitamin.")

If you're looking for immune support specifically, vitamin D3 outranks D2. Not only that, but taking a supplemental D2 may actually lower your body's circulating vitamin D3 (25-hydroxyvitamin D3) levels.

So, why is vitamin D3 better for immune health, and should you avoid D2 altogether? Let's break it down.

Why is vitamin D3 better than D2 for immune health?

Vitamin D3 is better for immune support than vitamin D2 for several important reasons:

1. D3 is more easily utilized by your body. While both forms convert to 25-dihydroxyvitamin D, which is the active form of vitamin D that the body makes, D3 has been shown to be approximately 87% more effective at raising serum 25-hydroxyvitamin D levels compared to D2.
2. Vitamin D3 is more effective at supporting genes associated with immune function than its plant-based counterpart, according to some research studies.
3. While both forms of vitamin D can be good to take if you have a deficiency, vitamin D3 is the superior choice for raising and maintaining optimal 25-hydroxyvitamin D levels for the long haul.

"Vitamin D3 is the first choice for healthcare practitioners for many reasons," explained Michael A. Smith, MD, director of education for Life Extension. "Most notably, it's the easiest form for your body to utilize, so you can correct deficiencies and stay strong against infections."

Here's a quick chart summarizing the two types of vitamin D and their roles in immune support.

While research confirms how vitamin D3 is best for immune health, none of this is to say that D2 is bad or that you should avoid D2, but if you have access to vitamin D3, it is the better choice.

What is the difference between vitamin D2 and D3?

Vitamin D2 and D3 have a different molecular structure, first and foremost. Additionally, D3 (cholecalciferol) and D2 (ergocalciferol) come from different sources. Vitamin D2 comes from plant sources, specifically, mushrooms and yeast. Vitamin D3, on the other hand, is made in the body from sunlight, and it's found in animal sources, such as fish and eggs, and sheep's wool. And surprise! Algae is a vegan source of D3.

While the body absorbs and uses both forms of vitamin D, the D2 form has lower binding affinity to vitamin D binding protein and is broken down (metabolized) and cleared from the bloodstream significantly faster than D3. Vitamin D3, in contrast, is more potent at equivalent doses and generally more effective at raising and maintaining vitamin D levels.

What does vitamin D do for the immune system?

Vitamin D isn't just a vitamin: it's also a hormone that plays a key role in immune system function:

• Vitamin D helps "turn on" certain genes to build a defense against germs, modulating one of the body's signaling systems to alert your cells to fight off viruses and bacteria.
• It acts like a project manager for your immune cells, making sure they communicate properly and stay in balance.
• Adequate vitamin D levels may prevent excess pro-inflammatory compounds in the lungs.

Given these key roles, it's important that you stay on top of your vitamin D levels. A vitamin D blood test can help you determine if you have a deficiency or sub-optimal levels, and your doctor or dietitian can guide you on how to raise your vitamin D levels back to a healthy range. It's possible they may suggest you take vitamin D2 if you are vegan, but for the reasons already discussed, vitamin D3 is often the preferred option.

Can vitamin D2 lower vitamin D3 levels?

Yes! While vitamin D2 can raise overall vitamin D levels in the blood, it also causes levels of vitamin D3 (25-hydroxyvitamin D3) to drop. This happens because both forms compete for the same "machinery" (pathways and cell receptors) in the body. A meta-analysis that included 11 studies found that there was a statistically significant reduction in 25-hydroxyvitamin D3 levels in those who received vitamin D2 supplements, compared to the control group without supplementation.

But don't worry, this concern only applies to supplements and not food intake: you can eat mushrooms and other plant foods that contain D2 without impacting vitamin D3 serum levels in your body.

Does vitamin D2 support immune health at all?

Yes, it can. However, while D2 can help correct a deficiency in the short term, it's less potent and effective at maintaining optimal levels over time.

In a meta-analysis of randomized, double-blind, placebo-controlled trials involving more than 11,000 participants combined, researchers found that the odds of having an acute respiratory infection were 12% lower among individuals taking vitamin D than among those who were not. This change was particularly prominent in individuals who were previously deficient.

Important note: If you learn you have insufficient levels of vitamin D, supplementing with any form is better than nothing. This could help explain why the meta-analysis found a reduced risk of infection among participants who supplemented with D2 or D3. But for long-term benefits, D3 is the way to go.

How much vitamin D3 do you need to support immunity?

This varies, but most people will likely benefit from around 2,000 IU to 5,000 IU daily, to start. Individuals who are overweight or those with naturally darker skin tones often require more. Your healthcare provider may recommend periodic blood testing to ensure that your levels are adequate and stable. The ideal range is 50 ng/ml to 80 ng/ml.

Is vitamin D2 effective if you're vegetarian or vegan?

Yes. If you have a vitamin D deficiency, D2 can help support healthy vitamin D levels and offer short-term immune support. But you can find vegan sources of vitamin D3 made from algae.

Can you improve your vitamin D levels quickly?

Yes! While factors like geography, gender, age, and unique physiology can impact how quickly you improve vitamin D levels, overall, healthy individuals can raise them within 2-3 months with lifestyle changes. Raise vitamin D levels by building sustainable habits, such as spending time outdoors, adding vitamin D-rich foods to your menu, and choosing the right dietary supplement.

Resources

• Allen LH. "Micronutrients — Assessment, Requirements, Deficiencies, and Interventions." The New England Journal of Medicine. March 2025. https://www.nejm.org/doi/full/10.1056/NEJMra2314150?utm_source=openevidence
• Durrant LR, et al. "Vitamins D2 and D3 Have Overlapping But Different Effects on the Human Immune System Revealed Through Analysis of the Blood Transcriptome." Front Immunol. February 2022. https://pubmed.ncbi.nlm.nih.gov/35281034/
• Heaney RP, et al. "Vitamin D(3) is more potent than vitamin D(2) in humans." J Clin Endocrinol Metab. March 2011. https://pubmed.ncbi.nlm.nih.gov/21177785/
• Jäpelt RB, Jakobsen J. "Vitamin D in plants: a review of occurrence, analysis, and biosynthesis." Front Plant Sci. May 2013. https://pmc.ncbi.nlm.nih.gov/articles/PMC3651966/
• Martineau AR, et al. "Differential Effects of Oral Boluses of Vitamin D2 vs Vitamin D3 on Vitamin D Metabolism: A Randomized Controlled Trial." J Clin Endocrinol Metab. December 2019. https://pubmed.ncbi.nlm.nih.gov/31199458/
• Martineau AR, et al. "Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data." BMJ. February 2017. https://pubmed.ncbi.nlm.nih.gov/28202713/

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The Life Extension Health News team delivers accurate information about vitamins, nutrition and aging. Our stories rely on multiple, authoritative sources and experts. We keep our content accurate and trustworthy, by submitting it to a medical reviewer.