Mushrooms: Vitamin D & immune support

8th Nov 2024

Mushrooms are a great addition to meals. They provide beta-glucans, vitamin D (if sun-exposed), protein and ergothioneine, a powerful antioxidant.

Health benefits

Researchers are uncovering some promising benefits of mushrooms:

• Cancer prevention – A higher intake of 18 g per day was linked to a lower risk of total cancer. We’re still figuring out which types of mushrooms are most effective or if these findings apply more widely.
• Brain & mental health – Small studies suggest that people who eat more mushrooms may have a lower risk of depression and perform better on certain cognitive tests.
• Unique nutrients – Mushrooms are not plants, so they offer unique compounds that you won’t find in many other foods.

They are a source of:

• Ergothioneine – an amino acid with strong antioxidant properties, often called the ‘longevity vitamin’ for its potential to prevent or slow cellular damage.
• Dietary fibres, like β-glucans – which support gut health, help lower cholesterol and may improve immune function.
• Polyphenols such as carotenoids, with structures unique to fungi.
• High-quality protein – with good digestibility and a complete range of amino acids (particularly in button and king oyster mushrooms).
• Essential minerals like selenium, phosphorus, potassium and iron.
• Vitamins B12, C and D (when exposed to UV light).

Just like us, mushrooms soak up the sun: They contain ergosterol in their cell walls, which converts into vitamin D2 when exposed to UV light. Common edible mushrooms like white buttons can produce up to 24 μg of vitamin D per 100g.

• Stable & cooking-friendly: They stay stable in the fridge for 7 to 10 days and cooking—like pan-frying without oil—retains up to 88% of their vitamin D2.
• Are they a good source? Vitamin D3 is considered more effective at increasing vitamin D levels but D2 from mushrooms can still make a meaningful difference, especially for people low on vitamin D, who get little sun or don’t eat animal products. (PMID: 38660061)

How much? Research suggests 4 portions of UV-exposed mushrooms a week for enough vitamin D, especially if you don’t get much sun or follow a vegan diet. One portion (80g) is about 3 handfuls of sliced mushrooms or roughly 14 button mushrooms.

What about mushroom supplements?

Mushroom powders are becoming popular in drinks and food but there are a few issues:

1. You don’t really know what’s in them: A recent study in the US found that only 26.3% of Reishi mushroom supplements actually contained the ingredients listed on their labels. We need more research in other countries to fully understand how widespread this is. (PMID: 28798349)
2. A spoonful of maltodextrin? It’s common to add fillers like maltodextrin, made from processed starches, to prevent clumping and inflate polysaccharide numbers. It’s fully soluble, so it mixes in without a trace. But recent trials suggest it might not be as harmless as we think, potentially affecting gut health and increasing inflammation. (PMID: 35230477)
3. Poor regulation & big marketing claims: Like with most supplements, mushroom powders aren’t tightly regulated, meaning manufacturers aren’t always held accountable for quality, safety or effectiveness.

If you buy them, it’s worth doing some research to find a trustworthy brand. We don’t have specific products to recommend but here’s what to keep in mind:

• Transparency & traceability – Check if they explain where the mushrooms come from, how they’re processed and list all ingredients, including the extraction method.
• Third-party testing – Look for brands that provide lab results to show they actually contain the active ingredients, with no fillers like maltodextrin and are free from heavy metals.
• Beta-glucan content – Look for products that list beta-glucan levels, as they are key compounds for health benefits.
• No added ingredients – Go for 100% mushroom products but remember fillers may not always be listed. It’s fully soluble, so it mixes in without a trace. (so starch analysis can help confirm they're filler-free).

In short, we still don’t know everything about these products – it’s a bit of a grey area with lots of unanswered questions.

But after reading all this, we hope you’ll be inspired to cook whole mushrooms and add them straight to your meals, fresh from the shop or farmer’s market. A whole food diet is always the better option!

How to enjoy

3 tips

1. Choose UV-exposed: Look for labels like “UV-treated” or “Rich in vitamin D” at the shop.
2. To wash or not? There’s a bit of debate since mushrooms can absorb water and lose texture. We think it’s fine to wash them, just do it right before cooking and pat them dry to get rid of excess moisture. You might need to cook them a bit longer to cook off any extra water.
3. Remove any plastic: Store mushrooms in a paper bag or cardboard box to prevent sogginess and mould.

3 ways to enjoy

1. Crispy side – Sauté them in a hot pan with olive oil and garlic until golden and crispy. Great with eggs, stews, pasta, fish, or even tossed into salads.
2. Ragu & stews – Mushrooms bring a rich umami flavour, making your dishes feel more filling and satisfying. They’re a great way to cut back on meat, too. Chop or grate mushrooms into minced meat to reduce saturated fat, stretch your meal, and add extra fibre and nutrients.
3. Stir fries with your favourite vegetables, a flavourful sauce and tofu, tempeh or fish.

If you’re not a fan (yet), experiment with cooking methods as they can massively change the texture and taste of mushrooms. Roasting can bring out their natural sweetness, while grilling adds a smoky flavour. Find a method that appeals to you!