Mushrooms and Cancer

By Nova Zhao and Subhas Ganguli

Introduction

Unfortunately the data on mushrooms is mixed. Please see the ‘warnings and cautions’ at the end of this article before coming to any conclusions.

Description

Mushrooms are edible fungi that live by extracting nutrients from dead and decaying matter.  They contain an assortment of proteins, vitamins, minerals, amino acids, antibiotics, and antioxidants, which can all be beneficial to our health (1). There are many varieties of mushrooms with a range of health benefits which have been used in traditional Chinese medicine because of their unique qualities (2).

Plain white (button) mushrooms (scientific name: Agaricus bisporus) are the cheapest and most widely available type of mushroom. Along with other varieties, they contain the amino acid L-ergothioneine, a powerful antioxidant that has shown to boost our immune system and protect cells against oxidative stress, which may be associated with cancer (3). This amino acid can help eliminate reactive oxygen species (ROS), which are free radicals released during the metabolic processes of cells that can cause significant damage and contribute to disease. Thus, ergothioneine, along with other antioxidants, is crucial in maintaining a balanced and healthy body (1,4). In vivo and in vitro studies of mushrooms have demonstrated many pharmacological effects, including antitumor, antiviral, hypocholesterolemic and hypoglycemic results, which will be described further in detail below (5).

How to Select and Store

There are many different types of mushrooms each of which offers distinct health benefits, so mixing them up within your diet will maximize their benefits for your health. Below are two common types of mushrooms and instructions on how to store them:

Shiitake Mushrooms

Shiitake mushrooms (Lentinus edodes) are currently the second most cultivated edible mushrooms globally; their production

has increased more than any other mushroom species (6). They contain 18 types of amino acids, providing nearly the ideal ratios of all amino acids needed for adequate human nutrition and have antitumor and anticancer properties that can boost the immune system (7). These mushrooms contain an abundance of L. edodes mycelium extract and lentinan. Lentinan can induce an antitumour and antiproliferative effect by activating different immune host responses, consequently increasing resistance against various types of cancers and possibly restoring immune function in affected individuals (8). Additionally, when exposed to UV sunlight, bioactive sterols contained in these mushrooms can be converted into Vitamin D, which can help us fight against diseases like the common cold. This is especially important, as a significant amount of the population suffers from vitamin D deficiency, particularly during the winter months (9).

How should shiitake mushrooms be stored?

Appropriate storage methods should be used to maximize the potential benefits of shiitake mushrooms on the human body. Unfortunately, freshly harvested shiitake mushrooms start deteriorating immediately, which can cause nutrient loss. Consequently, certain preservation methods can prolong its shelf-life, maintaining its quality and reducing nutrient loss (7).

First, the drying of shiitake mushrooms is one of the most important techniques in preserving its nutritional quality. It

minimizes microbial spoilage and reduces enzyme activity, which helps prolong its storage while maximizing its benefits (10). The most popular methods of drying currently in use are hot air drying, microwave drying, and vacuum drying, but each of these comes with several drawbacks that impact the nutritional quality of the mushrooms. A novel drying technique, microwave vacuum drying, increases drying rates at lower temperatures, distributes the energy more uniformly and efficiently, and prevents discolouration of the shiitake mushrooms, while preserving nutritional value (7).

Additionally, shiitake mushrooms treated with cinnamaldehyde, an organic compound that can be found in cinnamon, presented higher antioxidant capacity than treatments with thyme and clove. A study conducted by Jiang et al. showed that cinnamaldehyde was most effective in prolonging shelf-life, while reducing decay and susceptibility to mechanical damage. In fact, treatment with cinnamaldehyde also resulted in increased phenolic and flavonoid content, all of which induce antioxidant activity, consequently protecting cells against oxidative stress (6). Thus, treatment with cinnamaldehyde may help stimulate the many antioxidant properties that are unique to mushrooms.

It is highly recommended that you simply store loose shiitake mushrooms in a closed paper bag in the refrigerator, where they will remain fresh for approximately one week. Dried mushrooms should be stored in a tightly sealed container in either the refrigerator or freezer, where they can last from six months to one year. Refrigeration is important because many nutrients are susceptible to heat; thus, refrigeration can slow down the process of loss of nutritional quality (2). Commercially, L. edodes can be injected as a solution, taken as a tablet, capsule, concentrate, powder extract, syrup, tea, wine, or as a medicinal dish (11). Its easy accessibility and wide availability indicates its growing popularity in modern society.

White Button Mushrooms

White button mushrooms are commonly found in Europe and North America and are perhaps one of the most cultivated species of mushrooms in the world, like shiitake mushrooms. The polysaccharide portion of A. bisporus extract is often used medicinally because it is believed to have many beneficial properties, including immune-stimulating functions and antioxidant capabilities. In fact, it is currently being commercially developed as a dietary supplement as an immunostimulating agent and kidney tonic, while further research suggests that A. bisporus extract may even be beneficial in suppressing breast cancer hormones (8).

Interestingly, novel research shows that estrogen production in the breast may be significant in carcinogenesis; specifically, aromatase, a cytochrome P450enzyme complex, converts androgens to estrogens. A study conducted by Grube et al. demonstrated that the extract of white button mushrooms is a potent inhibitor of aromatase in vitro without toxic side effects; it is important to note that crude extract was used in the study to minimize potential changes in efficacy from the purification process (12). By inhibiting aromatase and reducing the production of estrogens, phytochemicals in white button mushrooms may have the ability to suppress breast cancer cell growth.

How should button mushrooms be stored?

Upon harvesting, mushrooms often immediately begin softening and browning in colour, due to the breakdown of enzymes in plant cells and loss of moisture through respiration. Storage at higher temperatures also speeds up the degradation process, thus reducing shelf-life and preservation of the mushrooms. In fact, a study conducted by Mohapatra et al. found that the lowest refrigeration temperature possible resulted in the least colour variation amongst the mushroom caps (13). Therefore, white button mushrooms should be stored in the refrigerator or freezer, depending on when you plan on eating them. They will have the highest nutritional quality and flavour when eaten and/or cooked fresh.

Tips for Preparing & Cooking

Because mushrooms have many pores, absorbing too much water can make them quite soggy. To dry them, simply wipe them with a clean paper towel without sacrificing their texture and/or taste. If fresh mushrooms become too dried out, you can soak them in water for approximately 30 minutes (2). Only trim the stem end if it is dry, and remember to trim the tough stem portion of shiitake mushrooms.

Certain methods of cooking are better for specific types of mushrooms. For example, you can try to sauté whites, crimini, oyster, and shiitake mushrooms, grill portabella and shiitake mushrooms, roast portabella, oyster, and shiitake mushrooms, and more (14). See here and here for recipes for basic preparation and cooking of different types of mushrooms.

Nutritional Profile

Generally, mushrooms are low in fat and energy, but contain an adequate amount of protein, dietary fibre, vitamins, and minerals. The crude protein content of edible mushrooms range from approximately 15% to 35% of the dry weight and is heavily dependent on the species, variety, and stage of development of the mushroom (5). Of the proteins present in mushrooms, they contain all the essential amino acids, and are especially rich in lysine and leucine (15). Approximately 50% to 65% of mushrooms are carbohydrates and 2% to 6% is fat matter, of which the majority is predominantly unsaturated fatty acids, especially linoleic acid (16). Digestible carbohydrates in mushrooms are usually present in small amounts, often in the form of mannitol or glucose, indicating that mushrooms are not a major source of energy for us (5). Mushrooms also contain significant amounts of potassium, sodium, calcium, phosphorus, magnesium, and most importantly, selenium (16). Additionally, they contain many vitamins, including thiamine, riboflavin, niacin, biotin, and ascorbic acid; however, the amount of vitamins present in mushrooms will vary depending on the species (15).

Overview of Possible Health Benefits

A meta-analysis of observational studies examined eight case control studies and two cohort studies, where a total of 6890 people were included, to investigate the correlation between dietary mushroom intake and risk of breast cancer. Meta-analyses for premenopausal and postmenopausal women were conducted separately to account for any differences that menopausal statuses may have on breast cancer risk. The results included a linear dose-response association between mushroom intake and risk of breast cancer, and the protective effects of mushroom consumption were consistently shown in both groups: premenopausal and postmenopausal women. At a daily mushroom consumption of 20 g, the relative risk of breast cancer was reduced by one third (~ 33%).  Additionally, sensitivity analyses were conducted and publication bias was accounted for, before considering the results of this meta-analysis. While mushroom type was not accounted for, as there are too many different types of edible mushrooms, it can be concluded from the meta-analysis that greater edible mushroom intake may be correlated with a lower risk of getting breast cancer (17). A case-control study from China (18) looked at dietary intakes of mushrooms and green tea and the risk of breast cancer. In China, the most common fresh mushroom consumed is the white button mushroom, whereas shiitake mushrooms are the most common dried variety. A daily intake of fresh mushrooms of > 10 g/day was associated with a 65% lower rate of breast cancer.  Similarly, an intake of > 4 g/day of dried mushrooms was associated with a 47% decreased rate of breast cancer.  The authors then looked at the combined effect of intakes of fresh mushrooms and green tea on breast cancer. A high intake of green tea and fresh mushrooms was associated with an relative 89% lower rate of breast cancer; similarly, with dried mushrooms, the reduction was 82% (18).

Another study conducted by Dai et al. in 2015 examined the correlation between mushroom consumption and immunity in humans. Specifically, participants were randomized to consume either 5g or 10g of dried shiitake mushrooms daily for four weeks, and the proliferation and activation of 2 innate lymphocytes, 𝞬𝞭-T and NK-T cells, were examined before and after consumption to measure immunity. After mushroom consumption, these cells responded robustly to mitogen, signaling improved immunity. Furthermore, after consumption, the cells produced less inflammatory mediators and more anti-inflammatory mediators, indicating improved immunity as well. Less inflammation during an immune response is often advantageous for the host because less energy is used to combat the pathogen through a less aggressive immune response (18). Therefore, this study demonstrates a positive correlation between dietary mushroom intake and improved immunity in young adults.

One possible benefit of mushrooms is a reduced risk of cancer. One of the most unique properties in mushrooms is its ability to act as an antioxidant, while improving our immune system and fighting against oxidative stress, which is strongly linked with cancer. Furthermore, mushrooms contain a wide array of nutrients, including all the essential amino acids, minerals, vitamins and more, allowing them to help us fight against illness and disease. Several studies have demonstrated the beneficial pharmacological effects of mushrooms, and correlations conducted amongst large samples have shown the correlation between improved physical health and increased mushroom consumption amongst humans.

Warnings and Cautions

In a study to assess the cancer potential of Agaricus bisporus,100 mice were fed raw mushrooms 3 days per week (with regular mouse chow for the other days) and compared to 100 mice fed regular chow. While overall survival was similar between the two groups, the mushroom-fed group had significantly more tumours of bone (16% vs 0%; P<0.05), forestomach (33% vs 2%; P<0.05), lungs (51% vs 30%; P<0.05) and liver (10% vs 1%; P<0.05). A recent meta-analysis of human studies showed a possible 20% increase in total cancer risk per 100 g of mushrooms per day (P<0.05) (20); however, this was only based on 2 studies, both of which examined the effects of the consumption of only raw mushrooms. A Japanese cohort study (21) looked at mushroom intake in 101,669 men and women. There was no increase in total mortality in men or women and no increase in all cancer mortality in men. However, in women, there was a 16% increase in all cancer mortality (P<0.05) in those eating enokidake and shiitake mushrooms 3 or more times per week (21).  Further analysis revealed an approximately two-fold increased risk of rectal cancer (P<0.05), but only 25 cases of rectal cancer occurred in the study. There was also an 87% increase in breast cancer based on 30 cases (P<0.05). A European prospective cohort study (22) of 25,531 participants 35-65 years of age followed for 8 years found that mushrooms did not increase the risk of chronic diseases, type 2 diabetes, or cardiovascular disease. There was a non-significant 17 to 24% increase (P>0.05) in the risk of cancer. Researchers who conducted a mouse-based study tried to calculate the health risk of mushroom consumption in humans and concluded that if 10,000 people consumed a mushroom meal daily for 70 years, then one more cases of cancer could be attributed to consuming mushrooms (in addition to the 3000 cases of cancer which would be expected from other causes) (23).

Specifically, it is the accumulation of agaritine (found in mushrooms) that can cause unexpected toxicological effects. However, a review done by Sorimachi and Nakamoto examines certain methods that can extract agaritine from mushrooms, consequently ensuring safety in its consumption. For example, it has been shown that agaritine can be removed completely from Agaricus blazei water extracts by ethanol fractionation without losing several biological activities (24). Furthermore, in another study, the effects of storing and cooking were examined in terms of concentration of agaritine (23). In fact, the storage of mushrooms in the refrigerator and freezer resulted in significantly lower agaritine content. While the amount of agaritine present is dependent on the length and condition of storage, the degree of reduction ranged from 20% to 75%. Additionally, when 20 g of sliced mushrooms were boiled in 250 cc of water for about 30 minutes, the concentration of agaritine in the mushrooms decreased by 75% as it was transferred to the broth (so if you threw away the broth and ate the mushrooms, you would only get ¼ of the agaritine).  If mushrooms were dry baked at 200’ C or microwaved (1000 W), there was a loss of agaritine content as shown in the table below (numbers represent percentage of agaritine content lost):

Thus, if mushrooms are microwaved for at least one minute, approximately 65% of the agaritine content is lost. Gathered data shows that agaritine content of cultivated mushrooms can be reduced through various methods, including storage in the refrigerator and freezer followed by thawing, in addition to cooking by boiling, dry baking, frying, and/or microwave heating. It should also be mentioned that canned mushrooms generally contain less than 10% of the agaritine content detectable in fresh mushrooms (23).

In summary, the data on mushrooms and cancer is mixed; in light of this, it would be best to limit intake until further definitive studies have shown their safety.

I would like to acknowledge and thank Tiffany Tse for her input into this article.

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