Women who regularly eat mushrooms, shiitake or other fungi, and drink a couple of cups of green tea every day, are at least ten times more likely not to develop breast cancer than women who don’t eat many mushrooms and hardly ever drink green tea. Epidemiologists at the University of Western Australia write about this in the International Journal of Cancer.
There’s a mountain of cell and animal studies all of which say that mushrooms contain substances that armour the immune system against cancer cells, inhibit the growth of tumours and that induce cancer cells to commit suicide. [Clinics (Sao Paulo). 2011; 66(12): 2133-9.] There are even phase-1 trials in which mushroom-extract supplements seem to be helping cancer survivors to improve their quality of life. [ISRN Oncol. 2012; 2012:251632.]
When it comes to epidemiology, however, indications of the protective effect of mushrooms are few and far between, except for a few Korean studies. One recent Korean study has shown that women who eat more than 12 g mushrooms every day are three times more likely not to develop breast cancer than women who only consume 3 g mushrooms every day. [Nutr Cancer. 2010; 62(4): 476-83.]
By the way, the most popular mushrooms in the Korean diet are the oyster mushroom [Pleurotus ostreatus], the shiitake [Lentinula edodes] and the ordinary mushroom [Agoricus bisporus]. According to the Korean studies, these reduce the chance of hormone-sensitive breast cancer in particular.
The Australian researchers wanted to know whether they could demonstrate the positive effect of mushrooms on breast cancer in China too. To do this they collected data on the diet of 1009 women who had secondary breast cancer tumours, and data on the diet of 1009 comparable women who did not have breast cancer. According to their calculations, women who eat more than 10 g fresh mushrooms every day are three times more likely not to develop breast cancer than women who only consume 2 g mushrooms every day.
The mushrooms the women ate most in this study were ordinary mushrooms, which they ate fried.
The Chinese have already amassed considerable epidemiological evidence that green tea reduces the chance of developing breast cancer, so for the sake of completeness the researchers also looked at green tea consumption. This is how they discovered that green tea reinforces the cancer-inhibiting effect of mushrooms.
Women who ate 10 g mushrooms or more every day and also drank tea brewed from at least 2 g green tea leaves were almost ten times less likely to develop breast cancer during their lifetime than women who drank little green tea and ate few mushrooms. A large cup of green tea, about 250 ml, requires about 4 g of tea leaves. It’s worth noting that many Chinese top up a cup of green tea with more water several times without adding new leaves.
“Our findings, if confirmed consistently in other research, have potential implications for protection against breast cancer development using an inexpensive dietary intervention”, the researchers conclude.