While a whole-food, plant-based diet confers huge health advantages – such as decreasing your risks of cancer, heart disease, and many other diseases – it is sometimes hard for vegans to get one important nutrient: Vitamin D.

Vitamin D is extremely important in a number of processes – from immune function to bone growth. In fact, “rickets” – the disease caused by weak bones and poor calcium levels – is directly related to Vitamin D intake. Before the advent of fortified processed foods, North America and Europe had a huge epidemic of rickets. Nearly 8 in 10 children suffered from this disease in the early 1900s!

While governments have since mandated that many foods like milk, cereal, and dairy products are fortified with vitamin D, people trying to eat healthy, unprocessed foods often miss out on these important vitamin D sources. While these foods are certainly healthier than cereal and other processed items, there is one major flaw with eating only whole, plant-based foods.

These foods, while healthy, contain close to 0% of your daily recommended value of vitamin D! In fact, the only source of vitamin D in a vegan diet is found in mushrooms.

In this post, we’ll dive into what vitamin D is, what it does in your body, and how you can use mushrooms as natural, healthy food to greatly boost your vitamin D levels!
What is Vitamin D?
Vitamin D is a small molecule that serves a very important role in your body. Active vitamin D regulates the level of calcium in your blood. Calcium ensures that your bones grow properly, your immune system functions as it is supposed to, and the nutrient is even involved in the mechanisms that cause and control muscular contractions!

Specifically, vitamin D influences how your gut absorbs calcium from your food. Vitamin D essentially increases the permeability of your gut lining, allowing calcium to easily be absorbed into your bloodstream. Within the bloodstream, calcium circulates to many organs that require it to function – especially your bones.

Your bones need lots of calcium to stay strong and healthy. Vitamin D increases calcium uptake, regulates calcium levels in the blood, and allows your bones to stay strong and allows many other organs to function properly.

Depending on your diet, there are many different sources you can get vitamin D from.
Natural Sources of Vitamin D
Fish is one of the most accessible sources of vitamin D in nature. According to the National Institutes of Health (NIH), one tablespoon of cod liver oil contains over 170% of your daily recommended value of vitamin D! So, if you eat lots of fish, you are likely to get all the vitamin D you need.

For the rest of us, this simply isn’t enough. Fortunately, humans can synthesize vitamin D from other molecules. However, this process only occurs when the skin is exposed to sunlight. Sunlight contains a large amount of UV light – needed to convert vitamin D precursors into active vitamin D that your cells can use.

Simply by sitting in the sun for a half-hour a few times a week, you can greatly increase the vitamin D levels in your blood. That’s great news for vegans that work outside! For those of us stuck inside during the best hours of sunlight, this process is not very helpful. Unfortunately, UV light cannot travel through windows.

In fact, many people (with many different diets) have grossly insufficient levels of vitamin D.
What Happens if you are Vitamin D Deficient?
Without vitamin D to regulate the calcium in your blood, calcium is withdrawn from bones in order to supplement blood serum levels. In effect, this slowly weakens your bones over time. This weakness can lead to rickets in children – a disease that causes mis-formed bones and growth defects.

In older adults, vitamin D deficiency can lead to osteoporosis – a term that literally means “holes in your bones”. These holes, created by the destruction of bone to maintain calcium levels, greatly weaken the bones of older adults. This can lead to an increased risk of hip fractures, muscle weakness, and fatigue.

In fact, due to a huge outbreak of rickets and osteoporosis in many European and American populations, many foods are now fortified with vitamin D. Cereal, milk (both cow and plant-based), and many other processed foods often have added vitamin D to ensure that the population does not suffer from rickets. However, these additions may only account for 10% of the daily recommended value. So, how is a person supposed to get all of the vitamin D they need? (Especially vegans!)
Mushrooms, a Huge Source of Vitamin D
Vegans (and everyone else) can get a massive amount of vitamin D by eating mushrooms. According to the same NIH report, one serving white button mushrooms exposed to UV light can give you up to 46% of your daily value of vitamin D!

That is nearly 4X the vitamin D available in fortified foods such as milk and cereal! Thus, one serving of mushrooms (UV-exposed) and 15 minutes of being outside in bright sunlight can give you all the vitamin D you need. In fact, mushrooms fall right below fish in a comparison of available vitamin D!

That being said, not all mushrooms are created equally. There are some very important differences between different kinds of mushrooms and how they are grown.
Pick the Right Mushrooms
There are several important considerations that dictate how much vitamin D a mushroom contains. Here are the most import things you should look for when buying mushrooms:
UV Exposed
For the same reason that humans need UV light in order to create vitamin D, mushrooms also need to be exposed to UV light in order to create vitamin D. The precursors of vitamin D require a lot of energy in order to be converted into an active form. This energy is supplied by the energy bound within UV light.

Disappointingly, many commercial mushroom farms grow their mushrooms indoors – completely blocking their exposure to UV light. Some mushroom growers have begun to understand the importance of UV light, and subject their mushrooms to an intense blast of UV light after they are harvested. This can massively increase the amount of vitamin D within the mushrooms.

If you can’t find UV exposed mushrooms, you can easily expose mushrooms to UV yourself. Simply place your mushrooms in the sun for 15 minutes before you cook them! Because the mushroom cells are still living, they can still convert the vitamin D precursor into the active form. In fact, UV exposure almost exclusively affects the vitamin D content of mushrooms, and will not reduce or remove any of the other great nutrients! Regardless of the type of mushroom you buy, UV exposure is the most important aspect of generating vitamin D.

Wild vs Cultivated
While mushrooms cultivated indoors often have less active vitamin D, they do have higher levels of ergosterol – a vitamin D precursor. When exposed to UV light, much of this precursor is likely converted into a more active form of vitamin D. One study found that many wild-picked porcini, chanterelle, and lactarius mushroom varieties contain high levels of active vitamin D. Wild-picked mushrooms are always exposed to some UV, which probably accounts for their higher levels of vitamin D.

That being said, wild-picked mushrooms can be hard to find and are less sustainable than commercially-grown mushrooms. If you prefer the grocery store to hiking around the woods, just make sure you allow your mushrooms to “sun-bathe” before you eat them!
Type of Mushroom
According to one study, the type of mushroom does not matter nearly as much as the UV exposure. Researches found significant levels of vitamin D in crimini (Agaricus bisporus), portabella (Agaricus bisporus), enoki (Flammulina velutipes), shiitake, maitake (Grifola frondose), oyster, morel (Morchella spp) and chanterelle (Cantharellus cibarius) mushrooms! Any of these mushrooms (if UV-exposed) serve as great sources of vitamin D, and eating mushrooms regularly was shown to significantly increase blood serum levels of vitamin D.

Other studies have found slight differences in the amount of vitamin D provided by various mushroom varieties. Researchers have found that vitamin D levels were moderate in shiitake and oyster mushrooms, and very high in morel, chanterelle, maitake (5.2–28.1 μg/100 g) and UV-treated portabella (3.4–20.9 μg/100 g).

So, if you really need a vitamin D boost, look for a nice UV-exposed portabella. You can also buy a non-exposed portabella and simply put it in the sun for 5-15 minutes! This should significantly increase the amount of vitamin D present.
Go for Variety!
Essentially, as long as your mushrooms are UV-exposed, you will be getting quite a bit of vitamin D. While this vitamin D comes in different forms from different mushrooms, all mushrooms express some levels of vitamin D. You can even take mushroom supplements and powders. Variety is the spice of life – so go big!

Try mushroom soups, sauteed mushrooms, stir-fry, mushroom bacon, or even raw mushrooms on a salad. With a steady stream of various mushrooms in your diet, you will get all the vitamin D you need. This is especially important for vegans – since vitamin D does not exist in any plant-sources.

Plus, people who think they are fine because they eat meat and eggs should be warned – meat and eggs have been shown to increase blood acidity. Higher blood acidity means calcium must be used to raise the pH of your blood and counter the acidity. So, even if you are getting a lot of vitamin D through the fish and eggs you eat, these foods may actually be decreasing the calcium in your blood!

However, if you reduce your animal protein intake and substitute with fresh, UV-exposed mushrooms, you can get the best of both worlds and ensure that your vitamin D levels are high enough to support your bones, body, and overall health.

Bon appétit!