It seems like vitamin D is all over the place recently — social media, news stories, research papers. Most of us grew up thinking that you got vitamin D from the sun and that was that, but it turns out that it’s actually more complicated than that. Not only does it play a bigger role in your body’s functioning than most of us know, but vitamin D deficiency is a serious issue that most people leave unaddressed. So what does vitamin D do for the body, and how can you make sure you get enough of it? Read on to learn why taking vitamin D is so important, the best foods for vitamin D, the link between vitamin D and immunity, and more.
So, What Does Vitamin D Do For the Body?
First off, vitamin D is not exactly a vitamin. Vitamins are essential micronutrients that our bodies need to survive, while vitamin D is actually something called a “prohormone.” Prohormones are substances that our body converts into hormones (think of them like probiotics for hormones). Basically, when you take in vitamin D, your livers and kidneys process it to turn it into a hormone that performs various functions in your 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. After the active hormone is released into the body, 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.
See, 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.
Besides this super important role, vitamin D also helps to reduce inflammation and modulate various processes, including cell growth and the metabolism of glucose (sugar). We’re also learning more and more about the close and complex relationship between vitamin D and immunity — which we’ll explore more in-depth, below.
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 Connection 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 functions that vitamin D carries out in immune function. First off, it is critical in activating our immune system defenses when it perceives a danger. Once that response has been initiated, vitamin D can enhance the function of immune cells that protect your body against pathogens (like immune cells on steroids, minus the steroids). It also modulates 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.
In fact, 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.
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 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 nearly half of all Americans are deficient in vitamin D.
There are a number of potential reasons for this, but the most likely culprit is twofold: first, it’s very difficult to get vitamin D through diet alone; and second, many of us don’t get enough of the right kind of sunlight needed to synthesize the vitamin (plus most Americans aren’t taking vitamin D supplements). 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.
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.” In other words, most people really need to be taking vitamin D.
The Best Foods for Vitamin D
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 getting sunlight and taking vitamin D 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. You’ll find not only our recommended vitamin D brands, but also many other supplements, personal care products, home cleaning products, food brands, air filters, vacuums, and more categories that our team has vetted and curated to ensure you’re buying the least toxic versions of everything. Once you’ve checked out the database, if you find it isn’t for you right now and just want one recommendation for a good vitamin D brand, we like Designs for Health 5000 IUs.
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 getting sunlight and taking vitamin D supplements, 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.
The WellBe Takeaway: What to Remember About 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.