Should You Be Taking Vitamin D? Vitamin D and Immunity, Best Foods for Vitamin D, and More

Vitamin D has become a hot topic in health conversations lately—on social media, in news reports, and through emerging research studies. Many of us grew up believing that vitamin D was simply “the sunshine vitamin,” something you get from sun exposure, and that was the end of the story. But the truth is much more nuanced. Vitamin D is essential to many bodily functions, and deficiencies in it are surprisingly common and often overlooked.

So, should you be taking vitamin D? What exactly does vitamin D do for your body? And how can you make sure you’re getting enough, whether from sunlight, diet, or supplements? This article digs deep into the science behind vitamin D, its relationship with your immune system, the best foods to get it from, and practical tips to optimize your vitamin D levels naturally.

You can also listen to an audio version of this guide on The WellBe Podcast.

So, What Does Vitamin D Do For the Body?

Vitamin D is often called a vitamin, but in reality, it’s more accurately classified as a prohormone. Unlike vitamins, which are essential nutrients that your body cannot produce, prohormones are substances your body can convert into active hormones. In the case of vitamin D, your body processes it into calcitriol, the active hormone form that carries out important functions. 

Here’s a breakdown of how vitamin D works in the body. 

• As you probably know, sunlight is one of the main sources of vitamin D. When your skin is exposed to certain wavelengths of sunlight (ultraviolet light with a wavelength of between 290 and 310 nanometers), it’s absorbed by vitamin D receptor cells, setting off a chain of reactions. 
• First, the cholesterol in your skin is converted into vitamin D3, which is then stored in your body’s fat cells. If you’re getting your vitamin D from food or supplements, it goes straight into your fat cells, skipping the cholesterol conversion on the skin.
• Once it’s in your fat cells, first your liver then your kidneys convert the vitamin D into the active form of the hormone your body needs, which is called calcitriol. 
• The active hormone is released into the body, where it takes on a crucial role in a number of different processes. Essentially, vitamin D helps to regulate your body’s levels of calcium and phosphate, both of which are essential for your overall health.

To provide more context, it’s important to understand that when you ingest calcium, your body can’t absorb it as it is. Vitamin D plays the role of the go-between, helping the calcium move from the intestines into your bloodstream, where it can then do all of the things you think of calcium as doing: strengthening and mineralizing your bones and teeth, promoting bone growth, preventing muscle cramps, and fending off bone disorders like osteoporosis and rickets. Without vitamin D, only about 10-15% of dietary calcium is absorbed; with adequate vitamin D, absorption can increase to 30-40%. 

Beyond bone health, vitamin D influences many other processes:

• It helps regulate inflammation in the body.
• It modulates cell growth and supports metabolic health.
• It influences glucose metabolism, potentially impacting diabetes risk.
• It has profound effects on the immune system (more on that in the section ).

One quick note: vitamin D comes in two forms, D2 and D3. When you get vitamin D from the sun, you obviously don’t get to pick what form of the vitamin you get (your body only makes vitamin D3 from sunlight), but you do have the choice when you get vitamin D from food or supplements. Most evidence indicates that vitamin D3 increases serum 25(OH)D levels to a greater extent and maintains these higher levels longer than vitamin D2, even though both forms are well absorbed in the gut.

The Relationship Between Vitamin D and Immunity

Many of us think of vitamin C and zinc as the big immune supporters, but the relationship between vitamin D and immunity is just as strong. See, all of our cells have vitamin D receptors, including immune cells. When those immune cells synthesize the active version of vitamin D (from sunlight, food, or supplements), the vitamin then acts on those cells, impacting their behavior in hundreds of ways. In broad strokes, that means that vitamin D can modulate and regulate our immune responses. 

Specifically, there are a few key roles that vitamin D plays in immune function:

• Activating our immune system defenses: In the presence of a pathogen or perceived danger, vitamin D helps protect your body by initiating an immune response.
•  Enhancing the function of immune cells. Vitamin D works to supercharge the cells that protect your body against pathogens—think immune cells on steroids, minus the steroids. 
• Modulating adaptive immunity.  Vitamin D influences T-cell behavior, promoting regulatory T cells that help prevent autoimmune reactions.
• Modulating the production of cytokines, which are proteins secreted by certain immune cells that help send signals from one cell to another. This is extremely important, because if there are too many cytokines, your immune system completely overreacts, which can lead to a hyperinflammatory condition that can actually kill you.

Notably, this “cytokine storm” is thought to be one of the ways that people die from Covid-19. Some research has suggested that a vitamin D deficiency is associated with a higher death rate from Covid, and researchers believe that this is because people without enough vitamin D can’t properly regulate cytokine production—so once the virus hits, their immune cells go into overdrive, and there’s no way to tell them to calm down.

Vitamin D and Covid: What’s the Connection?

Speaking of Covid, while we’re talking about vitamin D and immunity, we should also briefly note a couple of the dozens of studies currently looking into how vitamin D might prevent or treat the coronavirus. One study out of Chicago found that people with a vitamin D deficiency had a 1.77 times higher risk of contracting Covid than those with adequate levels of vitamin D (likely because those with adequate vitamin D levels could more effectively fight off the virus if exposed). 

In terms of treatment, one study out of Spain explored using vitamin D to treat patients hospitalized with Covid. They split them into two groups, one of which received best-available treatment plus a form of vitamin D, the other of which received only best-available treatment. Of those in the control group, 50% of patients entered intensive care and 8% died. Of those in the vitamin D group, 4% entered intensive care, and none died. It was a very small study, so it’s important not to extrapolate too far, but it suggests that the relationship between vitamin D and immunity might be central to finding effective treatment for and protection against Covid.

The most recent study from October 2020 found that over 80% of Covid-19 patients have vitamin D deficiency. This study was also small, only 216 patients, but the evidence is mounting so much so that the British government decided in November 2020 to begin giving out vitamin D to millions of vulnerable people to help protect them from Covid-19.

Why Most of Us Should Be Taking Vitamin D

Given how important vitamin D is for bone health and effective immune function, it should come as no surprise that it’s pretty bad to have a vitamin D deficiency. That’s why it’s particularly concerning to learn that up to 50% of the global population is vitamin D deficient or insufficient.  In the United States, nearly half of all Americans are deficient in vitamin D, with some groups experiencing higher rates.. 

There are a number of potential reasons for this, including: 

• Limited sun exposure. Many of us don’t get enough of the right kind of sunlight needed to synthesize Vitamin D. See, it’s not just any old kind of sunlight that produces vitamin D: we can only make vitamin D from only ultraviolet light with a wavelength of between 290 and 310 nanometers. To make matters worse, light of that wavelength doesn’t even penetrate the atmosphere in the north during the winter, making vitamin D deficiency even more widespread. Plus, all that sunscreen we dutifully wear to prevent skin cancer can further minimize vitamin D synthesis. 
• Dietary insufficiency: It’s very difficult to get vitamin D through diet alone. Few foods naturally contain vitamin D, and fortified foods don’t always provide enough.
• Skin pigmentation: Darker skin synthesizes less vitamin D from sunlight, increasing risk of deficiency.
• Age: Older adults’ skin produces less vitamin D.
• Health conditions: Some medical issues—like Crohn’s, celiac disease, and cystic fibrosis—affect vitamin D absorption or conversion.

Because vitamin D plays such an important role in the health of our bones and immune system, vitamin D deficiency is no joke. Not having adequate vitamin D levels has been associated with an increased risk of autoimmune conditions and increased susceptibility to infection and disease. It can also do harm to your bones, leading to bone loss, soft bones and other bone disorders in adults, and bone deformities in children. 

Vitamin D deficiency can also have repercussions outside of immunity or bones. It’s been associated with respiratory diseases like COPD and asthma, as well as high blood pressure and diabetes. As one professor and researcher told the Wall Street Journal, “I could make a list of 50 diseases. If you are D-deficient, then you have a higher risk of all these diseases.”

Now that we’ve established how essential vitamin D is, you probably want to know how to make sure you have adequate vitamin D levels. The two best ways to get vitamin D, hands-down, are sunlight and supplements. To get vitamin D from the sun, it’s best to go out midday, when UVB rays are the strongest and you don’t need to be out as long to make enough vitamin D (but remember, if you live in a northern latitude you can’t get vitamin D from the sun during the winter). 

In terms of taking vitamin D supplements, there are tons of great options available. For WellBe-vetted and approved recommendations, check out the WellBe Non-Toxic Product Database. 

The Best Foods for Vitamin D

Diet isn’t one of the primary sources of vitamin D, because it occurs naturally in so few foods. That’s why you’ll see a lot of products —particularly dairy products and cereals—fortified with vitamin D. So while you should definitely turn to supplements and sunlight for the bulk of your vitamin D, you can still get a good amount of it from certain foods. 

The best foods for vitamin D are:

• Oily fish: Oily fish like salmon, trout, mackerel, tuna, and sardines are all good sources of vitamin D, as is fish oil on its own which you can find in the WellBe Non-toxic Product Database.
• Mushrooms: All mushrooms contain vitamin D, but the highest concentrations can be found in maitake, portabella, and crimini, among others. What’s more, exposing the mushrooms to UV light before eating them actually increases their vitamin D levels!
• Egg yolks: All egg yolks have vitamin D, but the level depends on the sunlight exposure of the chickens and the vitamin D content of their food. Pasture-raised eggs come out on top for vitamin D levels, which are our recommendation anyway!
• Vitamin D-fortified foods: This one is pretty obvious, but it’s worth mentioning anyway. The most commonly vitamin D-fortified foods are yogurt, various types of milk (dairy, oat, soy, etc), orange juice, and cereal.

It’s also important to note that vitamin D is fat-soluble, so even if you’re eating all of the best foods for vitamin D, you won’t actually absorb the nutrient unless you eat it with some fat. So if you’re looking to get vitamin D from mushrooms, for instance, make sure you cook them in some oil or eat them with another fatty food, like avocado. 

Should I Take Vitamin D Supplements?

If you’re wondering, “Is it good to take vitamin D supplements?” the answer is likely yes for many people, especially during winter or if you have limited sun exposure.

Here are some key points to consider:

• Supplementation is the most reliable way to maintain optimal blood levels of vitamin D.
• Most adults require between 600 to 2000 IU daily, though some may need higher doses based on blood tests.
• Vitamin D3 supplements are generally recommended over D2 for better absorption and longer-lasting effects.
• It’s important to avoid excessive doses, as vitamin D toxicity can occur with extremely high intakes, though this is rare.

Before starting a supplement regimen, consider getting a blood test to check your 25(OH)D levels. Optimal levels are usually considered between 30 and 50 ng/mL (75-125 nmol/L).

The WellBe Takeaway on Vitamin D

The amount of vitamins, minerals, and other nutrients your body needs can be quite confusing, and it’s easy to get overwhelmed and not think much about it. With many nutrients, as long as you eat a varied and healthy diet rich in plants, that’s perfectly fine! But vitamin D is different. Fortunately, you don’t have to remember everything about vitamin D and how it works. Here are the key takeaways about the so-called sunshine vitamin: 

• Vitamin D isn’t actually a vitamin. Rather, it’s a prohormone, aka a substance that your body can convert into a hormone. Once we absorb vitamin D, it gets stored in your fat cells. Then when you need it, your livers and kidneys convert it into the active hormone you need. 
• There are two types of vitamin D: D2 and D3. They are both absorbed equally well in the gut, but most evidence indicates that vitamin D3 increases your vitamin D levels to a greater extent and maintains these higher levels longer than vitamin D2. 
• There’s a strong relationship between vitamin D and immunity. This is because vitamin D receptors exist on immune cells, and so when those cells create the active form of the hormone, the hormone can exert power of the cell and impact its function.
• Vitamin D activates and improves your immune system, regulates your immune response (i.e., prevents overreaction), and mounting research suggests that it may protect against or even treat Covid-19!
• Almost half of Americans are deficient in vitamin D. Vitamin D deficiency is associated with bone disease, autoimmune conditions, increased susceptibility to infection and disease, high blood pressure, and diabetes. 
• There are three sources of vitamin D: sunlight, supplements, and food.
• In order to synthesize vitamin D, you need UV sunlight with a wavelength between 290 and 310 nanometers. This wavelength doesn’t penetrate the atmosphere in winter months in northern latitudes.
• Food is not the primary source of vitamin D, as it’s not naturally present in many foods. The best foods for vitamin D are oily fish, mushrooms, egg yolks, and to a lesser extent, vitamin D-fortified foods like milk, yogurt, and cereal. 
• Taking vitamin D in supplement form is the best bet for getting adequate vitamin D. Check out the WellBe Non-Toxic Product Database for our WellBe-approved vitamin D supplements, fish oils and much, much more. 

How do you make sure you get enough vitamin D? Sunlight, supplements, diet, or a combo? Let us know in the comments below!

You can also listen to an audio version of this guide on The WellBe Podcast.

Citations:

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2. Bikle, D. Extraskeletal actions of vitamin D. Ann N Y Acad Sci. 2016 Jul; 1376(1): 29–52.
3. Aranow, C. Vitamin D and the immune system. J Investig Med. 2011 Aug;59(6):881-6.
4. Bivona, G. et al. The immunological implication of the new vitamin D metabolism. Cent Eur J Immunol. 2018; 43(3): 331–334.
5. Di Rosa, M. et al. Vitamin D3: a helpful immuno-modulator. Immunology. 2011 Oct; 134(2): 123–139.