Shiitake mushrooms have been used for centuries to boost immunity. Researchers have now found that taking as little as 5g dried shiitake mushrooms per day can have immune-boosting effects.
The golden-brown shiitake mushroom, Lentinula edodes, has been used medicinally for hundreds of years in Asia. Previous research identified one of the main active ingredients as a unique beta-glucan, named lentinan after its source. Lentinan is now used as an approved immunotherapy treatment for stomach cancer in Japan where it has been shown to prolong survival. Lentinan stimulates the activity of white blood cells, increases production of interferon (a natural anti-viral agent) and boosts the activity of a group of antioxidant enzymes, called superoxide dismutases, which have the unfortunate acronym of SODs.
Shiitake mushrooms boost immunity
A group of 52 healthy volunteers in Florida were randomised to add either 5g or 10g dried shiitake mushrooms to their diet (equivalent to one or two 80g servings of fresh mushrooms) every day, for four weeks. The dried mushrooms were supplied both whole and powdered for variety, and rehydration and cooking instructions were provided.
The volunteers gave blood and saliva samples before and after the study to measure their levels of various immune substances. After eating shiitake mushrooms for four weeks, significant improvements were seen in the proliferation and activity of first-line defence lymphocytes (gamma-delta-T cells) and natural-killer T-cells (which fight infected and cancerous cells).
Eating shiitake mushrooms also increased salivary levels of protective IgA antibodies, while blood levels of C-reactive protein (CRP, a marker for inflammation) reduced by 30% suggesting the mushrooms also had an anti-inflammatory action.
No differences were seen in the results from those taking 5g shiitake versus 10g shiitake mushrooms per day, suggesting that one serving of the mushrooms was sufficient to improve their immune and inflammatory responses. Of note, two people taking 5g mushrooms per day withdrew from the study because of a skin reaction, called shiitake dermatitis, which was thought to result from improper preparation of the dried mushrooms (under cooked), while three people eating 10g per day withdrew because of digestive symptoms.
Preparing and eating shiitake mushrooms every day is a bit of a palaver and does not constitute a varied diet. Most people would probably prefer to take a shiitake mushroom supplement.
Although no placebo group was included in this study to see if the immune changes that occurred were due to other factors such as seasonal changes, this small study does provide much-needed support for the medicinal benefits of this popular mushroom.
Shiitake mushrooms are now widely available in supermarkets and you can even grow your own using impregnated kits – though I must admit I never had much luck with them until I threw the kit on the compost heap. Now they’re sprouting every year.
Mushroom lasagne, anyone?
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