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Your immune system protects you against disease, but for it to work properly you need a sufficient intake of certain key nutrients, including vitamins B12, B6, C, D and folate, plus the minerals iron, selenium and zinc. These can all be obtained from mushrooms to a certain extent.1
The familiar, edible white, brown, button and chestnut mushrooms found in supermarkets provide small amounts of zinc and selenium, as well as vitamins B6, C and folate. However, you would need to eat 8kg of button mushrooms to get your nutrient reference value (NRV) of vitamin C, and 700g to obtain your NRV of vitamin B6 – and they provide no vitamin B12 at all.
Button mushrooms also supply just 9mcg of selenium per 100 grams, compared to around 55mcg (100% NRV) found in a typical single Brazil nut.
Some wild mushrooms contain small amounts of vitamin D, but only if they have been exposed to ultraviolet light. Even then, the vitamin D is in the plant form of D2 rather than the D3 'animal' form that is best for maintaining our vitamin D blood levels.
Most fresh retail mushrooms sold in the UK are grown in darkness in atmospherically controlled rooms, so their exposure to light is minimal. As a result, the vitamin D2 content of retail fresh button mushrooms is usually less than 1mcg per 100g.
However, when fresh button mushrooms are deliberately exposed to midday sunlight for up to two hours, they can generate as much as 10mcg vitamin D per 100g, which could supply all your daily NRV.2
Reishi mushrooms have been revered in China, Japan, Korea and Tibet for over 2,500 years. The Japanese term 'reishi' means 'spiritual mushroom', while in China, it is known as 'ling zhi' - the mushroom of immortality.
Of the six different colours of reishi mushroom (green, black, white, red, yellow and rare purple), red reishi (Ganoderma lucidum) is considered the most potent.
Red reishi has been used in Traditional Chinese Medicine to promote wellness and longevity. It contains at least 100 different substances, known as triterpenes (ganoderic, ganoderenic, lucidenic, and ganolucidic acids) which have a similar structure to steroid hormones.
In laboratory studies, these substances were shown to have antibacterial, anti-viral, anti-histamine, anti-allergy and anti-inflammatory properties.3
Preclinical studies found that reishi extracts increase the secretion of antibodies (IgA) and immune substances known as alpha-defensins within the gut, to help reduce the risk of gastrointestinal infections.4
When tested in 40 male footballers who were physically stressed due to high altitude and low oxygen levels, reishi extracts helped to boost their relative level of circulating immune cells (T-lymphocytes).5
Maitake (Grifola frondosa) is a medicinal mushroom that is a rich source of vitamin D and contains some vitamin B6. Its main immune-boosting effects are believed to come from mushroom beta-glucans, however.
In mice, maitake extracts increased phagocytosis levels (the process in which immune cells absorb and destroy invaders), the activity of NK (natural killer) cells and the secretion of immune-signalling chemicals. The overall effect was a significant stimulation of defence reactions.6
There is also evidence that maitake works well in combination with the ayurvedic medicinal herb ashwagandha, helping to boost immunity during times of stress.7
Shiitake mushrooms (Lentinus edodes) are increasingly found fresh in supermarkets and restaurants, but are more often bought dried and rehydrated for use. The stems can be a bit fibrous and chewy to eat, however.
Shiitake contain some vitamin D, vitamin B6 and vitamin B12. Their main immune benefits come from a unique mushroom glucan called lentinan, which is believed to boost the body's defences against viral and fungal infections.
In Japan, lentinan is extracted and given by injection as a biological response modifier to treat a number of medical conditions, including upper respiratory tract problems and conditions involving depressed immune function.8, 9 Studies in mice and cell cultures also show that lentinan helps to fight the influenza virus by suppressing viral growth.10
It's easy to add brown, button and shiitake mushrooms to your diet by slicing them raw into salads, sautéing them in olive oil with garlic and parsley, baking in the oven or adding to stews and other meals to supply nutritional value.
For some delicious recipe ideas, check out these delicious mushroom recipes.
Warning: Be careful when picking wild mushrooms to ensure accurate mushroom identification.
Dr Sarah Brewer is Healthspan's Medical Director and holds degrees in Natural Sciences, Surgery and Medicine from the University of Cambridge. Having worked as a GP and hospital doctor, Dr Sarah now holds an MSc in Nutritional Medicine from the University of Surrey and specialises in nutrition. She is also an award-winning writer and author.
Nothing beats a healthy, balanced diet to provide all the nutrients we need. But when this isn't possible, supplements can help. This article isn't intended to replace medical advice. Please consult your healthcare professional before trying supplements or herbal medicines.