Three really is the charm when it comes to vitamin D, according to a new study from the University of Surrey which found that vitamin D2 (the cheaper, plant/fungi-based form of the vitamin) was less effective at providing immune support than vitamin D3.

It's not news that vitamin D3 is more effective than vitamin D2 at boosting blood levels of the active form of vitamin D called 1,25-dihydroxyvitamin D. But what is eye-opening is how much more effective vitamin D3 is than its plant-based counterpart at supporting genes that are tied to immune function.

In this new study, researchers evaluated the impact from 600 IUs of both forms of vitamin D daily over a 12-week period during the winter in a cohort of 335 South Asian and white European women. Their findings? Compared to vitamin D2, vitamin D3 produced a greater effect on gene expression related to immune system defense against pathogens.

Specifically, compared to those taking D2, subjects taking the D3 form of the vitamin had increased production of interferons, which create a hostile environment for invaders (aka viral and bacterial infections, including respiratory infections and the cold and flu).

What is vitamin D?

Vitamin D, aka the "sunshine vitamin," has been documented in a myriad of research to impact virtually every aspect of human health. Most known as being important for bone health, the vitamin's benefits extend throughout the heart, brain, respiratory system and beyond—and, of course, include the health of your immune system.

That's because vitamin D is classified as a hormone, the only vitamin to fit this classification. As a hormone, vitamin D is produced by our own body and receptors are located on every cell.

Vitamin D intake: Is it better to take vitamin D2 or D3?

Vitamin D3, also called cholecalciferol, appears to be more beneficial than vitamin D2, also called ergocalciferol—not just for your immune system, but for your whole body. This is because research has long shown that compared with vitamin D2, vitamin D3 appears to be better at raising serum 25 hydroxyvitamin D concentrations (aka how much vitamin D is in your bloodstream).

Despite this, many may still believe that D2 and D3 are more comparable than they really are—but in fact, there appears to be a significant difference in the benefits offered by the ergocalciferol and cholecalciferol forms of the vitamin. In addition to the study out of the University of Surrey which has illustrated the superior immune health benefits of vitamin D3, other literature shows that vitamin D3 also has more heart health benefits than vitamin D2.

(Of course, if you are deficient in vitamin D, any vitamin D will be better than none!)

Why would a doctor recommend vitamin D2 instead of D3?

With vitamin D intake, vitamin D3 is usually the first recommendation you'll get from your healthcare practitioner rather than vitamin D2. However, a doctor might prescribe or recommend vitamin D2 over vitamin D3 if the patient was vegan and did not want to potentially spend more on vegan D3.

This comes down to the materials that are used to make the two forms of the vitamin. The main difference between vitamin D2 and D3 is that D2 is derived either from plants or fungi, while vitamin D3 is mostly produced from sheep's wool. Fortunately, in recent years, over-the-counter vegan D3 options have become more widely available, and the cost has come down, making the justification for choosing D2 less obvious.

How do you get a vegan vitamin D3? Some of the newer vegan vitamin D options are not derived from plants, but rather from algae or lichens. Algae are part of one of the four kingdoms of life known as "protists," which share some of the same characteristics as animals. It's because of this that certain species can synthesize vitamin D3 in response to UV light just like animals do.

Lichens are two or more organisms (usually between fungi and algae) functioning together in a symbiotic relationship. Fun fact: they cover about 8% of the world's land surface!

How much vitamin D per day offers immune benefits?

When it comes to vitamin D, doses are personalized—and a high dose isn't necessary for everyone. Most people will require 5,000-8,000 IU (125 mcg-200 mcg) daily. Those who are overweight or obese and those with naturally darker skin tones will often require a high dose of vitamin D.

It's a good idea to have your serum 25-hydroxyvitamin D concentrations measured before and after vitamin D intake to see what your starting point is with vitamin D. This test can also let you know if you have a vitamin D deficiency. Once maintained and healthy, you should periodically check back on your levels to make sure they're still where you want them to be, and increase to a higher dose if necessary.

Immune benefits of vitamin D

Vitamin D has been shown to bolster immune function. How? Research suggests that:

• Vitamin D may interfere with viral replication
• The vitamin also can repair cellular linings in the body
• The immune system's production of protective proteins against infection may get a boost from vitamin D
• Excess pro-inflammatory compounds in the lungs can be prevented with adequate D levels
• Vitamin D improves gene expression of immune cells to defend against pathogens, specifically through interferon signaling (as was demonstrated in the new University of Surrey study of vitamin D2 vs D3).

Given this vitamin's importance to a healthy immune system, it's not surprising that additional research shows that having adequate D levels may cut down on the severity of certain illnesses. In a meta-analysis of randomized, double-blind placebo-controlled clinical trials, the odd of having acute respiratory infection was 12% lower among those taking vitamin D, compared to the odds of those who were not taking vitamin D.

What other vitamins support the immune system?

It's important to note that vitamin D on its own usually isn't enough to provide optimal support of your immune system. Your immune function likely will be much stronger when other immune nutrients such as vitamin C and zinc are also taken together with vitamin D. Vitamin C supports healthy T cells to keep your immune system strong, and it also has benefits for your heart, brain, and even your iron levels. And zinc is an important mineral that supports immune health as you age.

A well-rounded routine is always a good idea, whether you are seeking to optimize immune response, overall wellness, or have another condition-specific concern.

How to get enough vitamin D3?

Maintaining optimal vitamin D levels is not something that commonly happens by accident. For most people, diet and sunlight are not enough to maintain optimal serum 25-hydroxyvitamin D concentration levels and will need to take 5,000-8,000 IU (125 mcg-200 mcg) of vitamin D daily. But a higher dose may be required, depending on your lifestyle and current vitamin D status.

If you're concerned about vitamin D deficiency, or having suboptimal D levels, taking lab tests for serum 25 and a vitamin D intake strategy should get you to your goal. But be patient—it takes time to turn around a vitamin D deficiency!

Vitamin D status: What is vitamin D deficiency?

Vitamin D deficiency is defined as having vitamin D levels below 20 ng/mL, while optimal blood levels of 25-hydroxyvitamin D are commonly considered to be over 40 ng/mL. (A note about vitamin D status: observe that there is a distinction between being deficient and not having "optimal" levels, meaning that you have enough vitamin D to experience its benefits. Life Extension defines optimal blood levels as between 50 and 80 ng/mL.)

A vitamin D deficiency can affect everything from your immune system to brain function—it even can play a role in erectile dysfunction. Having an inadequate vitamin D status has also been linked to worse outcomes for people with type 1 diabetes, type 2 diabetes, and autoimmune diseases including multiple sclerosis.

How much vitamin D do we get from sunlight?

We mostly get our vitamin D naturally from the UVB rays of sunlight, but two people in the same place at the same time can produce significantly different amounts of vitamin D. It varies from person to person, but even more highly between those with naturally darker skin tones.

Overall, approximately 42% of Americans are vitamin D deficient, but for Black and Latinx individuals, vitamin D deficiency is at significantly higher prevalence of 82% and 69%, respectively. All in all, people with darker skin require at least 3-5 times longer than a person with a white skin tone to achieve the same increase in vitamin D levels from UVB radiation. In fact, one study in Norway found that if Caucasians spent 30 minutes baking in the midday summer sun, it produced a rise of active vitamin D equivalent to taking 10,000-20,000 IUs (a high dose).

How much vitamin D do we get from food?

Diet has only a modest effect on raising vitamin D levels because most foods have little to none of this nutrient. The highest animal sources of vitamin D3 include eggs and fish such as salmon or tilapia.

The top vegan sources of vitamin D2 are:

• Mushrooms

• Soy milk and almond milk

• Tofu

If you don't eat a lot of these vegan foods and aren't a carnivore, non-food sources of vitamin D are going to be the best way to keep you from becoming D-deficient.

Should you sunbathe to get more vitamin D?

No, sunbathing is not a healthy way to increase your vitamin D levels! We need to be concerned about getting too much sun exposure, as this is the greatest risk factor for skin cancer (and cancer is not something you want if you're worried about a healthy immune response). Exercise caution by wearing sunscreen with an SPF of at least 30 if you will be in sunny locations for long periods of time.

Of course, this is a moot point for much of the world: for many people, their geographic location and busy schedules do not allow them to maintain optimal levels of vitamin D naturally from sunlight.

No matter where you live, of course, extra vitamin D intake is a safe way to make sure you're getting enough of this life-critical vitamin, and you don't need to find a spot on the beach or worry about getting a nasty sunburn if you take the right dose of vitamin D. Just make sure you choose the right kind: vitamin D3.

References

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• Cicarma Emanuela et al. "Sun and sun beds: inducers of vitamin D and skin cancer." Anticancer Res., September 2009, https://pubmed.ncbi.nlm.nih.gov/19667143/
• Durrant, Louise R. 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://www.frontiersin.org/articles/10.3389/fimmu.2022.790444/full
• Forrest, Kimberley Y Z et al. "Prevalence and correlates of vitamin D deficiency in US adults." Nutr Res., January 2011, https://pubmed.ncbi.nlm.nih.gov/21310306/
• Garland, Cedric F et al. "Meta-analysis of all-cause mortality according to serum 25-hydroxyvitamin D." American journal of public health, August 2014, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4103214/
• Grant William B. "Review of Recent Advances in Understanding the Role of Vitamin D in Reducing Cancer Risk: Breast, Colorectal, Prostate, and Overall Cancer." Anticancer Res., January 2020, https://pubmed.ncbi.nlm.nih.gov/31892604/
• Holick, Michael F. "Sunlight, ultraviolet radiation, vitamin D and skin cancer: how much sunlight do we need?" Adv Exp Med Biol., 2014, . https://pubmed.ncbi.nlm.nih.gov/25207357/
• Martineau, Adrian R 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/
• Nair, Rathish et al. "Vitamin D: The "sunshine" vitamin." Journal of pharmacology & pharmacotherapeutics, April 2012,https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3356951/
• Saz-Lara, Alicia et al. "The Comparative Effects of Different Types of Oral Vitamin Supplements on Arterial Stiffness: A Network Meta-Analysis." Nutrients, February 2022, https://pubmed.ncbi.nlm.nih.gov/35267985/

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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.