For a long time, scientists have promoted fruits and vegetables to help reduce the risk of heart disease, stroke and some cancers. It is unlikely that any one nutrient or compound in food provides the protection against future disease. It is far more likely that the synergy of many compounds in food combine effectively to offer protection to the body.
With mushrooms offering so many nutritional and antioxidant benefits the next step was to check the mushrooms effect on the broader human physiology. Preliminary reports indicate that mushrooms do indeed boost immune function.
Many of these studies have focused on exotic mushrooms, but researchers at Tufts University found that white button mushrooms enhanced the action of Natural Killer Cells in mice (Wu 2007), reduced the severity of arthritis in mice (Chandra 2011) and stimulated the production of anti-microbial peptides (Kuvibidila 2010). Another report from Pennsylvania State University showed that mushroom extracts given to mice reduced inflammation and increased the anti-cancer immune response (Yu 2009).
Since then researchers at the University of Western Sydney have shown that mushrooms increase the production of salivary IgA in healthy humans, an indicator of IgA levels at other mucosal sites such as the intestinal and respiratory tract (Jeong 2011). In a follow-up study they identified two mushroom polysaccharides that inhibit breast cancer cell growth, possibly through enhanced macrophage function (Jeong 2012).
It is not surprising that mushrooms have been found to play their part in lowering cancer risk, even though they are neither fruit nor vegetable. Research shows that mushroom extracts reduced breast cancer growth (Chen 2006). “Eating 100 grams, or even less, of mushrooms per day could have an effect on preventing new breast cancers”, said lead researcher Dr Shiuan Chen. Dr Chen has begun human clinical trials and we await the outcome of those trials.
In 2009, research from the University of Western Australia showed that women who ate an average of only 10g of mushrooms a day had a 65% lower risk of breast cancer (Zhang 2009). They undertook a diet and lifestyle interview with 1009 Chinese women with breast cancer and 1009 matched controls. Compared to those having no mushrooms, women eating 10g or more of mushrooms each day reduced their risk of breast cancer by over 60%. This protection was further enhanced if the women also consumed a cup of green tea (1g dried leaves). The effect was seen in both pre- and post-menopausal women. The most common mushroom consumed was the common button mushroom Agaricus bisporus.
Two other studies have also shown a link between mushroom eaters and a much lower risk of breast cancer, in the order of 50-60% compared to women who don’t eat mushrooms (Hong 2008, Shin 2010). Because three studies show a similar effect, it has stimulated more human research to see if breast cancer risk reduction in women is specifically due to compounds in mushrooms.
The mushroom has been linked to cancer prevention for some time. How could mushrooms be helping to protect us? Part of the answer may be because the mushroom contains compounds that suppress two enzymes called aromatase and 5-alpha-reductase (Grube 2001; Chen 2006). Aromatase converts the hormone androgen to estrogen, which in turn can promote the development of breast cancer, especially in post-menopausal women. Currently, aromatase inhibitors are being used in the treatment of estrogen-dependent breast cancer. Aromatase has been found in other cancers, such as ovarian, uterine and prostate cancers and there is speculation that aromatase inhibitors may have a significant role in preventing such cancers (Hong 2006).
The enzyme 5-alpha-reductase converts testosterone to dihydro-testosterone and is thought to play a role in the development of prostate cancer and benign prostate enlargement. The inhibitors of this enzyme reduce the incidence of prostate cancer. Research on animal cells in vivo suggest that mushrooms could have a role in protecting men against prostate cancer (Chen 2004). The same team found that button mushrooms reduced prostate tumour size and tumour proliferation, and increased tumour cell death, in mice (Adams 2008).
There have been two reviews of research on the potential for mushrooms to reduce the risk of cancer by enhancing the immune system (Borchers 2008; Ziadman et al 2005). The two mushroom components with the most supporting evidence appear to be the beta-glucans and peptide-bound polypeptides.
The glucans stimulate the phagocyte system (eg macrophages and monocytes) that consume alien cells. Mushrooms also contain lectins (bio-active proteins), and other compounds that have been strongly linked to a reduction in the risk of cancer and could potentially be helpful in the treatment of cancer (De Mejía 2005, Jedinak 2008).
Although it is too early to say that eating mushrooms will stop you from getting breast or prostate cancer, the future looks very promising for the role mushroom could have in reducing the risk of these two common cancers. On-going research in both human and laboratory studies will determine if mushrooms play a specific role in protecting against cancer.