Chaga mushroom (Inonotus obliquus) is a parasitic Polyporus from the Hymenochetaceae family. This fungal species has only been described in the northern hemisphere. Chaga can be particularly found in Canada, in the north of the United States of America, Kazakhstan, Siberia, Ukraine, Japan, South Korea, China, and in Europe (mostly in the northern and eastern parts of the continent). This fungus infects hardwood trees mainly from the genus Betula (birches), and to a lesser extent, those from the genera Quercus (oaks), Populus (poplars), Alnus (alders), Fagus (ashes), and Acer (maples).
The chemical analysis of Chaga in scientific literature revealed several compounds such as polysaccharides, triterpenes, and polyphenols, which might be responsible for most of the therapeutic effects. Tetracyclic triterpene called inotodiol has antiproliferative properties, demonstrated in vitro with human lung adenocarcinoma cells (A549) cancer-derived cells or HeLa. In addition, 2 other components derived from birch are frequently described in Chaga including betulin (or betulinol) and betulinic acid. Several species of birch are, indeed, used in traditional medicine with a very wide geographical distribution. The spectrum of pharmacological properties associated with their uses is important: antimicrobial, antidiabetic, hepatoprotective, antiarthritic, and anticancer activities. These last 2 activities were the most studied, especially from betulin and betulinic acid.
From historical chronicles, The Khanty people, an ethnic group from Siberia formerly called the Ostyaks, used Chaga mushroom in traditional medicine for different therapeutic indications: as an anthelminthic, as an antitubercular, to cure digestive disorders (gastritis, ulcers, etc), or even to prevent cardiac or hepatic illnesses. They used the crushed asexual form of the Chaga in several ways: by infusion, inhalation, or maceration in water of the charcoal obtained after burning to make body soap, which was used as an antiseptic. Furthermore, the utilization of the Chaga in Siberian gulags is mentioned in Alexandre Soljénitsyne’s book Le Pavillon des cancéreux (Cancer Ward). Soviet health authorities noticed a decrease of the incidence of cancer cases in this population and assumed that the consumption of this infusion was a protective factor against cancer.
The extracts of Chaga have been used in China, Korea, Japan, Russia, and the Baltics for their favorable effects on lipid metabolism and cardiac function, as well as for antibacterial, anti-inflammatory, antioxidant, and antitumor activities. Chaga extracts were found to inhibit hepatitis C virusand human immunodeficiency virus and demonstrated strong antioxidant and immunostimulatory activities in vitro. At the same time, animal studies revealed that aqueous extracts of I. obliquus exhibited anti-inflammatory effects in experimental colitis and promoted lipid metabolism. The mushroom has the ability to increase peroxisome proliferator-activated receptors γ transcriptional activities, which are expected to be therapeutic targets for dyslipidemia and type 2 diabetes.