Chaga (Inonotus obliquus): a medical marvel but a conservation dilemma?

Abstract

Chaga (Inonotus obliquus): a medical marvel becomes a conservation dilemma .-Sydowia 72: 123-130. Fungi have a rich history of medicinal use within many cultures. In most cases it is the fruiting body that is harvested and appreciated. Historical use of the species Inonotus obliquus is different, in that it is a conk-like structure of sterile mycelial mass formed in a pre-sporulation phase, that is utilized. Analysis of 7,516 occurrence records shows a largely circumboreal distribution and further investigation reveals an affinity for tree hosts in the Betula genus. The medicinal benefits of this sterile-mass, known as 'Chaga' have recently been proven with potent anticancer, antioxidation, anti-inflammatory and antidiabetic activity having been reported. However, the academic interest in this species has fuelled a boom in the commercial exploitation of a product that is almost exclusively harvested from the wild. The huge harvesting of this organism in its pre-reproductive (pre-sporulation) phase rises significant issues. The medicinal properties of this species are discussed along with the conservational concern. Possible alternatives, such as cultivation are discussed along with a call for urgent educational and legislative approaches to protect a species with a rich pattern of use by cultures both contemporary and historically.

Full text

Sydowia 72 (2020) 123
DOI 10.12905/0380.sydowia72-2020-0123 Published online 6 May 2020
Chaga (
Inonotus obliquus
): a medical marvel but a
conservation dilemma?
Paul W. Thomas1,2,*, Waill Ahmed Elkhateeb3 & Ghoson Mosbah Daba3
1 University of Stirling, Stirling, FK9 4LA, UK
2 Mycorrhizal Systems Ltd, Lancashire, PR25 2SD, UK
3 National Research Centre, El Buhouth St., Dokki, 12311, Giza, Egypt
* e-mail: paul.thomas@stir.ac.uk
Thomas P.W., Elkhateeb W.A. & Daba G.M. (2020) Chaga (Inonotus obliquus): a medical marvel becomes a conservation di-
lemma. – Sydowia 72: 123–130.
Fungi have a rich history of medicinal use within many cultures. In most cases it is the fruiting body that is harvested and
appreciated. Historical use of the species Inonotus obliquus is different, in that it is a conk-like structure of sterile mycelial mass
formed in a pre-sporulation phase, that is utilized. Analysis of 7,516 occurrence records shows a largely circumboreal distribution
and further investigation reveals an afnity for tree hosts in the Betula genus. The medicinal benets of this sterile-mass, known
as ‘Chaga’ have recently been proven with potent anticancer, antioxidation, anti-inammatory and antidiabetic activity having
been reported. However, the academic interest in this species has fuelled a boom in the commercial exploitation of a product that
is almost exclusively harvested from the wild. The huge harvesting of this organism in its pre-reproductive (pre-sporulation)
phase rises signicant issues. The medicinal properties of this species are discussed along with the conservational concern. Pos-
sible alternatives, such as cultivation are discussed along with a call for urgent educational and legislative approaches to protect
a species with a rich pattern of use by cultures both contemporary and historically.
Keywords: medicinal mushrooms, traditional medicine, secondary metabolites, conservation, cultivation.
The species Inonotus obliquus, is a wood-rot fun-
gus of living trees. The fungus enters through wounds
within the tree and from there may develop for an
estimated 10–80+ years causing decay and forming
a sterile mycelial mass (Lee et al. 2008). The sexual
stage begins once the tree is killed and fruiting bod-
ies are formed beneath the bark. However, it is the
pre-sporulating sterile mycelia mass that is most
often observed and occurs as a conk-like structure
or a black growth on the exterior of the tree (see
Fig. 1). The exact role of this sterile conk is still un-
known and although it contains chlamydospores,
infection is thought to arise from basidiospores pro-
duced by the fruiting bodies (Lee et al. 2008). Col-
lecting 7,516 geotagged records from the Global
Biodiversity Database (www.GBIF.com, accessed
11am GMT 31st of January 2020), representing ten
separate herbarium and occurrence databases, it is
clear that this species has a largely circumboreal
distribution (see Fig. 1). However, whether this dis-
tribution of occurrence records represents one spe-
cies with a broad geographic range or multiple re-
lated species with some anatomical similarities, re-
mains to be elucidated. The sterile conks are referred
to by many names but the most common is ‘chaga’
and they have a long history of use by local popula-
tions, often the hard woody mass is boiled to make
a tea, which is drunk to treat a range of conditions,
including cancers, viral and bacterial infections, and
gastro-intestinal disorders (Spinosa 2006). For ex-
ample, the Khanty people of western Siberia use this
species to treat heart and liver disease as well as for
general internal cleaning (Saar 1991). In recent years
this species has enjoyed a renaissance with a wealth
of papers now published, dedicated to its medicinal
use and health benets. These range from an anti-
oxidant effect (Cui et al. 2005) to immune-stimulat-
ing resulting in dramatic anti-cancer properties
(Kim et al. 2006). Indeed, I. obliquus is now one of
the most intensely researched of all medicinal fungi.
Here, alongside a review of the current understand-
ing of the medicinal properties of this species, we
discuss the unfolding conservational conundrum
arising from overharvesting and suggest ways in
which this may be mitigated.
Purported medicinal properties
Chaga has been found to contain a host of phar-
macologically active compounds that benecially

124 Sydowia 72 (2020)
Thomas et al.: Chaga – a conservation dilemma?
affect human health (Zjawiony 2004, De Silva et al.
2013). The biological activity of I. obliquus is mainly
due to the presence of several polysaccharides, con-
stituting the following sugars: rhamnose, arabinose,
xylose, mannose, glucose, and galactose (Hu et al.
2017). Additionally, in the last decade, several stud-
ies have reported biological activities of I. obliquus
such as anticancer, antioxidation, anti-inammato-
ry, antidiabetic and enhancement of immunity
(Choi et al. 2010). Remarkably, a number of studies
demonstrates little or no side effects during use in
disease treatment (Wasser 2002, Choi et al. 2010,
Elkhateeb et al. 2019). The biological activities of
I. obliquus are discussed below.
Antioxidant activity
Various compounds extracted from Chaga have
been reported to exhibit an antioxidant activity.
Nakajima et al. (2007) illustrated superiority of the
antioxidant activity (both superoxide and hydroxyl
radicals scavenging activities) of a hot water ex-
tract of Chaga in comparison with those of other
medicinal fungi namely Agaricus blazei mycelia,
Ganoderma lucidum and Phellinus linteus. Further
determination of the antioxidant potential of the
isolated fruiting body (spore-generating mass) and
Sclerotium (Chaga) revealed that an 80 % metha-
nolic extract of the fruiting body had a higher po-
tential than that of Chaga decoction.
Antidiabetic
Chaga extracts (CE) function as an antidiabetic
through the lowering of blood glucose levels. Poly-
saccharides, which represent one of the main com-
ponents of CE are capable of inhibiting alpha-glu-
cosidase, a carbohydrate-hydrolysing enzyme.
Hence, CE may act as a hypoglycemic agent by re-
tarding glucose absorption in digestive organs and
thus preventing hyperglycemia following meals
(Chen et al. 2010, Lu et al. 2010, Wang et al. 2017).
Sun et al. (2008) and Xu et al. (2010), reported that
polysaccharides of I. obliquus are capable of reduc-
ing glucose, triglycerides, fatty acids, and choles-
terol levels in blood.
Anti-inammatory activity
Causes of inammation can range from wounds,
burns, infections, stress, free radicals, radiation and
allergies, to immune system disorders. Drugs reduc-
ing inammation are called anti-inammatories.
Van et al. (2009) tested several different types of ex-
tractions from Chaga, for their ability to reduce in-
ammation. All of those tested signicantly inhib-
ited inammation, including a water-based poly-
saccharide extract and an ethanol-based extract.
Kim et al. (2007) and Choi et al. (2010) found similar
results with ethanol extracts.
Anticancer activity
The anticancer activity of CE is perhaps the
most widely reported health benet and that which
has received the most interest. The cytotoxic and/or
apoptotic effects of CE have been demonstrated in
numerous in vitro studies in cancer cell lines, in-
cluding the human colon cancer cells and the hu-
man hepatoma HepG2 cells (Youn et al. 2008). Poly-
Fig. 1. The sterile conk-like mass of Inonotus obliquus (left), known as ‘Chaga’, growing on Betula pendula (phot. Paul W. Thomas,
near Pitlochry, Scotland, UK) and the circumboreal distribution of Chaga from 7,516 geotagged records from the Global Biodi-
versity Information Facility https://www.gbif.org/occurrence/map (right).

Sydowia 72 (2020) 125
Thomas et al.: Chaga – a conservation dilemma?
saccharides isolated from I. obliquus sclerotium
have a direct antitumor effect due to protein syn-
thesis inhibition in tumour cells. Also, polysaccha-
rides derived from the mycelium of I. obliquus func-
tion by activating the immune system. Due to the
limited toxicity of these substances, both extracts
as well as isolated and puried chemicals may be a
good alternative to current chemotherapy and have
potential for a role in cancer prevention (Stanisze-
wska et al. 2017).
Heteropolysaccharides and homoglucans isolat-
ed from the sterile conk as well as endopolysaccha-
rides present in the mycelium differ in the mecha-
nism of antitumor activity; polysaccharides from
sterile conks act directly on the tumour cells and
endo-polysaccharides act indirectly by activating
the immune system in a way similar to bacterial li-
popolysaccharide (Kim et al. 2006). The triterpenoid
inotodiol showed the strongest anti-proliferative
effect on breast cancer Walker 256 cell line (Nakata
et al. 2009). Kang et al. (2015) reported that ergos-
terol peroxide acts as an antiproliferative agent and
also inhibits the colony formation ability of tumour
cells HCT116, HT-29, SW620 and DLD-1 cell lines
of colon. The Ergosterol peroxide from I. obliquus
exhibits anticancer activity by down-regulation of
the β-catenin pathway in colorectal cancer and it
shows that it down-regulated β-catenin signalling;
this proves that I. obliquus can be developed as a
promising medicine to treat colon cancer (Kang et
al. 2015). Nakajima et al. (2009) show that phenolic
compounds of methanolic I. obliquus extract dem-
onstrate a target toxicity against several lines of
cancer cells and the absence of cytotoxic effects
against normal cells.
Summary of identied medicinal compounds and
their action
Over 200 compounds have been extracted and
identied from I. obliquus (Rogers 2011). These
compounds belong to various chemical groups such
as lipids, carbohydrates, polyphenols, and terpenes.
The list of compounds extracted from I. obliquus in-
cludes but are not limited to β-sitosterol, fecosterol,
episterol, β-glucans, xylogalactoglucose, phelligri-
dins D, 3,4-dihydroxybenzalacetone, inonoblins A,
vanillic acid, syringic acid, ferulic acid, trametenol-
ic acid, p-hydroxybenzoic acid, foscoperianol D.
Some of the biologically active compounds extract-
ed from I. obliquus actually originate from the host
tree itself and these include betulin, betulinic acid
and such compounds are absent in cultivated strains
grown in the laboratory. Some of the biologically
active compounds extracted from I. obliquus are
listed in Table 1.
Tab. 1. General compounds extracted from I. obliquus and their biological activities.
Compound Chemical group Biological activity References
Betulin Terpenes Antibacterial, protective effects against
cadmium induced cytotoxicity
Oh et al. (2006), Géry et al. (2018)
Betulinic acid Terpenes Antibacterial, anti-malarial, anti-inam-
matory, anti-HIV activities and cytotoxic-
ity against a variety of tumor cell lines
Yogeeswari & Sriram (2005),
Kvasnica et al. (2005), Crevelin et
al. (2006), Moghaddam et al. (2012)
Inotodiol Triterpenes Anticancer, inhibits cell proliferation Nomura et al. (2008), Zhong et al.
(2011), Géry et al. (2018)
Lupeol Triterpenes Anti-inammatory and anti-cancer Saleem (2009)
Caffeic acid Polyphenol Anti-cancer, inhibits cell proliferation Kuriyama et al. (2013)
Trametenolic acid Sterol Anti-inammatory Ma et al. (2013)
Melanin Melanins Antioxidant, protect DNA from damage Babitskaya et al. (2000)
3,4-dihydroxybenzalacetone Polyphenol Anticancer, regulates expression of genes
promoting, anti-apoptosis, and cell
proliferation.
Sung et al. (2008), Kuriyama et al.
(2013)
Glucans Carbohydrates Immune modulator Lindequist et al. (2005)
Ergosterol peroxide Sterol Anticancer, antimicrobial, immunosup-
pressive
Merdivan & Lindequist (2017)
Inonoblin A Polyphenol Antioxidant Lee et al. (2007)
Phelligridin D Polyphenol Antioxidant, anti-inammatory Lee et al. (2007)

126 Sydowia 72 (2020)
Thomas et al.: Chaga – a conservation dilemma?
Figs. 2–5. Different products containing Chaga. 2. Inonotus obliquus tablets supplement (https://www.vitaminshoppe.com),
3. I. obliquus supplement capsules (www.mycomedica.eu), 4. I. obliquus fermented (www.kz.iherb.com), 5. I. obliquus extract
(www. emersonecologics.com).

Sydowia 72 (2020) 127
Thomas et al.: Chaga – a conservation dilemma?
Commercial exploitation and conservation
Commercial exploitation of Chaga-based products
The intense medicinal interest has resulted in a
rise in the awareness of Chaga within the wider
population. For example, a Google Trend analysis
reveals that the search-term ‘Chaga’ has increased
in popularity, four-fold in the last 10 years (to 2019).
Consequently, Chaga-based products are now wide-
ly available, primarily as dried and powdered wild-
harvested sterile conk. A recent search for ‘Chaga
health products’ returned 1,390,000 hits on google.
com (accessed 11am BST 1st of October 2019) and
Amazon.com currently list over 4,000 products with
the keyword ‘Chaga’ (accessed 11.30am BST 1st of
October 2019). The wide range of products, from
oral capsules to powdered ‘tea’ are presented as
having some form of heath or nutritional benet
and products derived from mycelial growth are con-
sidered inferior to those of wild-harvested sterile
conk (Kukulyanskaya et al. 2002). Examples of such
products are displayed in Figs 2–5.
A growing conservational worry and the potential
role of cultivation
Intense interest in, and the resulting harvest of,
natural products for commercial exploitation can
have a serious ecological impact and this has been
observed in other medicinal fungi such as Cordyceps
(Stone 2015). The concern is that I. obliquus may also
be vulnerable to commercial harvesting practices.
Although one previous attempt has been made to as-
sess the sustainability of Chaga harvesting (Pilz
2004), the report is over 10 years old and precedes the
current unprecedented demand whilst also ignoring
the unknown impact of harvesting the sterile conk
on the full life cycle of I. obliquus. Worryingly, the
rising interest in Chaga has not resulted in any fur-
ther attempts to assess either the direct or indirect
ecological impact of increased harvesting pressure.
The slow growing nature of I. obliquus, taking
many decades to form reproductive structures and
combined with the ease of sterile conk harvest at a
pre-sporulation stage, puts this species at theoreti-
cal threat of over collection. Importantly, the sterile
conk forms perennially whereas the spore-bearing
portion only occurs once in the lifecycle, as the tree
(or part thereof) dies (Lee et al. 2008). Indeed, we
are now in a situation where we are commercially
harvesting large quantities of an organism of which
we know very little about, with disregard for any
ecological impact on the target species or those that
may be interdependent.
One obvious remedy is to develop Chaga cultiva-
tion. Although I. obliquus is easily cultured, the
products derived from mycelial growth are consid-
ered inferior and do not contain the full suite of
bioactive compounds found within wild-harvested
sterile conk (Kukulyanskaya et al. 2002). Therefore,
a cultivation method is needed that would allow
harvesting of the sterile conk mass and this has pre-
viously been reported (Silvan & Sarjala 2017).
Silvan & Sarjala (2017) inoculated live and ma-
ture trees with mycelium that had been grown in
culture and after 3 years harvestable Chaga had
been produced. Host specicity should be taken
into account in any cultivation attempt and al-
though this species is often found with trees in the
Betula genus, there are other options. For example,
using the Mycology Collections data Portal (https://
mycoportal.org, accessed 11am GMT 31st of January
2020), a detailed database of records from across
Fig. 6. Host tree records at genus or species level for entries of
I. obliquus in the Mycology Collections Data Portal (https://
mycoportal.org). The genus Betula, in total, accounts for
89.4 % of records.
North America, information can be found on host
tree frequency. Analysing 599 records, we found 66
contained information about the tree host. Of these,
59 (89.4 %) were in the Betula genus, three (4.5 %)
were in Quercus, three (4.5 %) were for the species
Ostrya virginiana and one (1.5 %) for Acer rubrum
(see Fig. 6). These are records from North America
only and there may be other potential hosts, includ-
ing species from other continents. However, cultiva-
tion by inoculating live and mature trees may have
other unintended consequences. Firstly, this method
is dependent upon mature trees and so it would in-
volve modication of existing ecosystems. Secondly,

128 Sydowia 72 (2020)
Thomas et al.: Chaga – a conservation dilemma?
standard practices that would be used to aid culti-
vation, such as strain selection to develop rapid
maturation and aggressive growth, may pose anoth-
er unintended ecological threat. Releasing such an
enhanced strain of this parasitic fungus, optimised
to rapidly infect mature standing trees, into the en-
vironment runs the risk of threatening delicate
woodland habitats through rapid tree loss. Instead,
perhaps, cultivation efforts should focus on novel
indoor practices to produce sterile conks. Such
methods are commonly utilized for other edible and
medicinal wood-rotting fungi (Stamets 2011). This
way, strain selection would focus on traits that ben-
et indoor cultivation on substrates other than ma-
ture living trees. Further, developing systems to
produce sterile conks rather than mycelial extracts
may lead to better acceptance in the marketplace of
‘cultivated’ products.
A call for action
An understanding as to the threat posed by over-
harvesting of this species is urgently needed. In
2004 signicant harvesting pressure was already
noted (Pilz 2004) and no attempt has been made
since then to investigate the impact on wild popula-
tions. In addition to advances in cultivation a multi-
pronged approach is now needed to prevent damage
to wild population of I. obliquus and interdepend-
ent species. Firstly, an education programme within
areas where there is largescale and systematic har-
vesting, would be benecial to highlight the unique
lifecycle of this species and its role within fragile
habitats. Secondly, far more research is essential to
understand the current distribution of I. obliquus,
the impact of Chaga harvesting on this species’ life-
cycle and any unintended secondary consequences
of harvesting practices. Thirdly, legislative support
is necessary for the protection of I. obliquus until
such time as the impact of systematic and large-
scale harvesting can be assessed. However, this nal
point is not a small task considering the geographic
spread and consequently the numerous differently
governed regions in which this species occurs. Nev-
ertheless, urgent action may be necessary. Harvest-
ing during a pre-sporulation phase and the long
lifecycle combined with our lack of knowledge
means that if we don’t act soon, there is the poten-
tial for signicant damage to be done.
Conclusion
Arising as a sterile mycelial mass on the trunk of
its host tree and with a circumboreal distribution,
Chaga has a rich history of medicinal use by local
populations. Recent investigations have conrmed
the medicinal properties and prevalence of poly-
phenolic composites of not just Chaga but also the
mycelium and fruiting bodies of I. obliquus. Ex-
tracts from I. obliquus do indeed show much poten-
tial with signicant properties that may have been
appreciated historically, including: immune boost-
ing, anti-inammatory, antidiabetic and antibacte-
rial. However, it is the anticancer properties that
are currently receiving the most interest with the
glucan and triterpenoid prole presenting the use
of I. obliquus in some cases as a direct antitumor
agent. Clearly, further research and clinical trials
are needed to explore these medicinal properties
more fully.
The recent medicinal interest in I. obliquus has,
however, come at a cost to this organism. With over
4,000 products listed on Amazon alone, the scale of
the commercial exploitation is evident. Chaga prod-
ucts are almost exclusively produced from wild-
harvested pre-sporulation mycelial mass. The mass
harvesting of this organism, in its pre-reproductive
stage rises serious concerns for the survival of the
species. Where harvesting pressure has been ob-
served elsewhere, such as with Cordyceps spp. there
has been a signicant deleterious impact on the dis-
tribution and size of the population. The relatively
long life-cycle of I. obliquus increases this species
vulnerability.
Conservational action is now needed, and we
suggest a multipronged approach of further re-
search, an education programme within the har-
vesting areas, legislative support and a move to-
wards more sustainable approaches such as cultiva-
tion and development of products based on the cul-
tivated mycelium of this species rather than its
wild-harvested mycelial mass. By raising awareness
and international collaboration, we may be able to
mitigate damage to populations of I. obliquus and
interdependent species.
Acknowledgements
We would like to thank Miss Savannah Knowles
for her help in collating data from national records
databases.
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(Manuscript accepted 17 February 2020; Corresponding Edi-
tor: I. Krisai-Greilhuber)