With the earliest recorded use of medicinal mushrooms dating to 450 BC, human knowledge and use of these intriguing fungi go back for millennia. The fungi kingdom has many distinct differences from the plant kingdom, as fungi are not capable of photosynthesis and are, therefore, heterotrophic, absorbing nutrients from organic material in their surroundings (unlike plants, which obtain glucose through photosynthesis). In addition, although plant cell walls are composed mainly of cellulose, the cell walls of fungi are composed of chitin and glucans. In most fungi, the predominant polysaccharide found in the cell wall is β-glucan. Mushrooms, the fruiting bodies of macrofungi, also contain numerous other bioactive constituents, such as unsaturated fatty acids, triterpenes, phenolic compounds, glycoproteins, and peptides.
β-1,3-Glucan is the most abundant β-glucan polysaccharide found in fungal cell walls, comprising 65%–95% of total β-glucan content. Although many components of mushrooms may have medicinal properties, much of the research on mushrooms' medicinal activities has focused on β-glucan content, as we will discuss below. In fact, innate immune system function may have close ties to these compounds. Monocytes, neutrophils, macrophages, and dendritic cells all express β-glucan receptors on their surfaces.
These receptors (including dectin-1 receptors, complement receptor type 3 [CR3], and CD5) play a role in recognizing β-glucan as a fungal cell wall component. This recognition, in turn, activates phagocytosis, increases production of reactive oxygen species, and enhances the inflammatory response by activating numerous cytokines, helping the body to respond to fungal pathogens.
β-Glucans are structurally diverse, and this diversity may have implications for the way the body responds to these compounds both in the case of defense from fungal pathogens and infection, and in the case of therapeutic immune stimulation. β-Glucans also bind CR3. CR3 may be the primary β-glucan receptor on natural killer (NK) cells and neutrophils, and serves to upregulate cytokine production, and also controls fungal killing and phagocytosis in a complement-dependent manner. β-Glucans may also be fermented by intestinal bacteria, possibly leading to beneficial changes in the composition of the host microbiome.
In addition to featuring prominently in traditional cuisines around the world, mushrooms are extracted to create a variety of supplements, with medicinal mushrooms representing a burgeoning billion dollar industry globally. Mushroom extracts may be created by a variety of methods, with extraction methods playing an important role in the final chemical composition and constituents of a supplement.
For example, ethanol extraction may lead to a mushroom supplement higher in total phenolic content, creating a supplement with good antioxidant potential. Hot water extraction, in contrast, yields a mushroom extract with much higher β-glucan content (since polysaccharides are water soluble). Combined extraction produces a mushroom extract with both water-soluble and ethanol-soluble constituents. Clinicians should keep these extraction methods in mind when choosing a mushroom supplement, as different extracts may be better indicated in specific situations.
Medicinal mushrooms have been the subject of extensive research in many areas, and clinically are frequently selected to help support immune function or to help patients with viral infections, cancer, cognitive concerns, and other health conditions. Each of these areas provides fascinating insights into how these mushrooms work, and how they might be our allies in helping our patients achieve better health.