by Christina Papazoglou
Silver birch is a medium-sized deciduous tree with a characteristic silver-white trunk that peels off in layers and a light canopy with elegant, drooping branches (Forestry Commission). Throughout human history, almost every part of Silver birch has found various medicinal applications, either internally or externally (American Cancer Society, 2008). In traditional medicine different parts of the Silver birch are used to treat ailments like urinary tract infections, kidney and bladder stones, oedema, hair loss, skin rashes and rheumatism (Chevallier, 2000; ESCOP, 2003). In the last decade, the isolation of some certain compounds (betulin and betulinic acid) from the bark of the birch has attracted the attention of the scientific community as a possible antiviral and antitumour agent (American Cancer Society, 2008). Several studies have been performed to investigate the mechanism of action of the different parts of the Silver birch as well as the antitumour activity of betulinic acid and derivatives (Bruneton, 1999, Wichtl, 2004). Beyond the clinical trials that have been conducted to prove the efficacy of birch leaves and bark, there are no pharmaceutical formulations of Silver birch in the UK and further studies are needed to find out whether they are safe and effective (American Cancer Society, 2008). This article aims to give a review of information concerning the Silver birch, providing a detailed analysis of its biological and medicinal uses as well as its toxicity to the general public.
Photograph above: Silver Birch in NE corner of Mecklenburgh Square Garden near to the Herb Spiral
Silver birch (Betula pendula Roth,) also known as the European white birch, is grown mainly in the northern parts of Europe and Asia (Van Wyk and Wink, 2004). The name is thought to have derived from the Sanskrit word bhurga, meaning “tree whose bark is used to write upon” and it was used as a living signpost by cutting symbols into birch trunks as messages for other passing that way (Chevallier, 2000). Within the birch family (Betulaceae), Silver birch is one of the most common species in Britain naturally growing here since the end of the Ice Age (Forestry Commission; Kew Royal Botanic Gardens).
Photograph above: Windswept silver birch tree, Beaulieu Heath, New Forest by Jim Champion [CC]
Silver birch is a hardy tree, also known as a pioneer species, meaning is one of the first trees to engage an appropriate habitat. It is one of two native birches. Many of the birch trees that we see in Britain and Ireland are not true Silver birches but hybrids between Betula pendula and the Downy birch, Betula pubescens Ehrh. (Renou et al., 2007). Both species share some of the same habitats, although Downy Birch is more common in Scotland (Forestry Commission). The feature that distinguishes Silver Birch from the rest of the Birch trees is its flaking silver-white bark (Royal Horticultural Society [RHS], 2015).
Photographs: Silver birch catkins (Dean Morley, 2009), Silver birch leaves (Dean Morley, 2012)
Silver Birch is an elegant, fast growing deciduous tree, with a characteristic silver-white peeling bark and a light canopy (Van Wyk and Wink, 2004). As the tree matures, the bark develops large black diamond-shaped fissures (Natural History Museum). It grows up to 30m in height (but usually it attains about half this size) and over 80 years old (or exceptionally 100 years). The large branches are pointed upwards but the twigs and smaller branches are pendulous, giving it a weeping crown (RHS, 2015).
The glabrous leaves of Silver birch are approximately 2.5-6.0cm long and 2-5cm wide, triangular to rhombic, with sharply double-serrate margin and toothed edges (Atkinson, 1992). The upper surface of Silver Birch leaf is dark green and the lower is lighter green. There are numerous punctiform oil glands on both surfaces (Evans et al., 2002; Wichtl, 2004). Silver birch is a monoecious tree, meaning both male and female flowers are found on the same tree. Flowers appear in the form of cylindrical catkins that are pollinated by the wind (Van Wyk and Wink, 2004). Slender male flowers are long, loosely hanging in groups of two or four at the tips of shoots, pale yellow catkins, while female catkins are shorter, green and stand upright when in bloom (RHS, 2015). The tiny seeds have small, papery wings for wind dispersal and they ripen from July to August. Before seeds are dropped they hang like “lamb tails”. In April, both male and female catkins are found on the tree, and the leaves turn yellow from late summer into autumn before they fall (Forestry Commission). Taste, astringent and bitter (Wren et al., 1988).
Silver birch is common in Europe, temperate parts of Asia and in North America, though in Southern Europe it is found at higher altitudes only. Silver birches are a typical pioneer tree species with rapid early growth and they are found naturally amongst open woodland and heaths. It is also planted decoratively and for ecosystem services in parks and gardens (Chevallier, 2000). Silver birch is suitable for almost every kind of soil (clay, chalk, sand, loam) and situation. They prefer slightly acid, sandy soil, although they can grow in neutral and basic (alkaline) soils as well (Forestry Commission). Birch cultivation requires sunny or bright places, as it cannot grow in the shade. They grow best in well-drained soil and they prefer cool climates (Renou et al., 2007). The birches have very shallow roots so it is necessary for the soil surface to be excessively moisturised and air ventilated (RHS, 2015). They can stand the wind but not maritime exposure. Local weather and soil conditions will determine the final height and shape of the tree. The buds are collected in March, the same applies for sap in spring, whereas the gathering of leaves takes place in April-May in open woodland and heaths. The bark is usually obtained from trees that have been felled for timber in spring and can be distilled at any time of the year.
Historical and modern uses
Silver birch is now mainly planted for its aesthetic value and as a nursery tree to protect young forestry plantations (Forestry Commission), but various Silver birch tree parts and products have been important since ancient times and have been used in folk and traditional medicine in many different forms (herb, extract, tar, essential oil, infusion etc.) (Demirci et al., 2004; Mashentseva, 2011).
Silver birch has been used as a medicinal herb in northern Europe and Asia since the earliest times (Chevallier, 2000). Because of its wide range of pharmacological and physiological actions, the medical applications of its products are extensive (Mashentseva et al., 2011).
In the past, the leaves of Silver birch were used in Great Britain for their antiseptic properties and as a tea to treat kidney and bladder stones, urinary infections, gout, rheumatism and oedema. During the Napoleonic wars, the sap from the birch was so revered, that it was described as a universal panacea for the peasant and gentry alike. The pharmacological action of the bark for the treatment of wounds was described by Hildegard of Bingen, while Indians in North America used a decoction of birch bark both as a laxative to relief constipation and for diarrhoea prevention as well (Herbal Encyclopedia, 2010).
Traditionally, Silver birch is used to treat several problems related to the urinary tract, rheumatism, gout, hair loss and various skin conditions (ESCOP, 2003). The leaves are bitter and astringent, and are used as diuretic and anticholesterolemic. They are effective for the treatment of kidney, bladder and urinary tract infections such as cystitis, urethritis and are recommended as a reliable solvent of kidney and bladder stones. They are also used as supportive treatment for rheumatic ailments. A Herbal tea made from the leaves of Silver birch is recommended in Germany as a diuretic and for special diets. Silver birch sap is a mild diuretic while the birch buds are also used as an antiseptic and wound healing agent (Chevallier, 2000; Mashentseva et al., 2011). The interest in Silver birch is focused on the antiviral, vascular and antitumour activity of its bark. The bark of Silver birch is used externally for the treatment of warts, eczema, psoriasis and other skin conditions (American Cancer Society, 2008) while recently, one of the compounds that has been isolated from the bark demonstrates cytotoxic properties for the treatment of human melanoma and other tumours (Williamson and Wren, 2003). Other claims for birch bark are its diuretic and laxative activity. Silver birch tar is applied topically against irritations and parasites (Tyler et al., 1976). Due to the characteristic pleasant aroma, birch products such as essential oils, have also found many applications in cosmetics and related personal care products (Demirci et al., 2004).
Parts used medicinally: Leaves (Betulae folium), bark (Betulae cortex), leaf buds (Betulae gemmae), tar oil from bark (Betulae pix) (Van Wyk and Wink, 2004)
Photograph: Autumn birch (James Jordan, 2007)
Some Scientific Evidence
Diverse phytochemical investigations of Silver birch have shown that the main components are flavonoids, phenolics, saponins, tannins, volatile oils including methyl salicylate, and terpene derivatives (Demirci et al., 2004). Specifically, the bark of the Silver birch contains proanthocyanidins and considerable amounts of triterpenoid derivatives such as betulin, betulinic acid and oleanolic acid, tannins and saponins. The outer part of bark contains up to 20% betulin (Evans et al, 2002; Williamson and Wren, 2003).
The leaves of the Silver birch contain about 3% flavonoids (according to the European Pharmacopoeia not less than 1.5% calculated as hyperoside) including hyperoside (up to 0.8%), myricetin galactoside, quercitrin and other glycosides of quercetin, kaempferol and myricetin. The low concentration of essential oil (0.1%) contains sesquiterpene oxides, while other constituents of the leaves are monoterpene glycosides, triterpene alcohols and esters of the dammarane type (ESCOP, 2003; Wichtl, 2004).
The main components of tar oil (produced by destructive distillation of the bark) are phenolics (6%), such as guaiacol, cresol and pyrogallol, while the buds are rich in essential oils (main components: α-copaene, germacrene D, and δ-cardinene) (Demirci et al., 2004; Van Wyk and Wink, 2004).
Leaf: The diuretic or aquaretic effect of Silver birch leaves is ascribed to its flavonoid content. Various flavonoids were investigated for their inhibitory activity on specific enzymes responsible for the regulation of the formation of urine through excretion of sodium ions (Grundemann et al., 2011). In addition, the increased volume and flow of urine in the urinary tract may contribute to the prevention of urinary and renal calculi. In vivo and in vitro experiments (on rats, mice, rabbits, dogs) show that certain flavonoids, especially quercetin and other phenolic compounds present in Silver birch leaves, are responsible for its diuretic activity (Wichtl, 2004). In vitro investigation of the anti-proliferative capacity of Silver birch leaf extract on human primary lymphocytes, led to the conclusion that this extract would be effective for the treatment of immune disorders, like rheumatoid arthritis, by diminishing proliferating inflammatory lymphocytes (Grundemann et al., 2011). The in vitro and in vivo evaluation of the antioxidant activity of the Silver birch in the lipid peroxidation procedure in brain tissues has resulted in the realisation that the extract of the buds has the highest effect (comparable with the effect of the standard antioxidant Vitamin E) (Mashentseva et al, 2011).
Bark: The bark of Silver Birch is a source of betulinic acid. Betulinic acid is cytotoxic in vitro and in vivo: it causes a process of self-destruction, called apoptosis, to certain types of tumour cells (such as human melanoma cells, brain tumour cells including medulloblastoma and neuroblastoma) and certain amides of it are potent and selective inhibitors of HIV-1 replication (Bruneton, 1999; American Cancer Society, 2008).
Bark: In a German non-randomized clinical trial (2006) a birch bark extract was shown to be effective in treating actinic keratosis, a pre-cancerous skin condition. However, until now (June 2015) only non-pharmaceutical skin care products are available on the market. Further studies are needed to demonstrateits safety and efficacy in humans (American Cancer Society, 2008).
Leaf: Various different formulations of the birch leaf have been studied for efficacy.
In a field study, the dry aqueous extract of birch leaf showed to be effective for irrigation of the urinary tract in patients suffered from urinary tract infections, irritable bladder, stones or miscellaneous complaints.
In a randomized, double-blind placebo-controlled pilot study, the treatment of patients suffered from infections of the lower urinary tract with birch leaf tea, proved to be effective when compared to the results of the control group (ESCOP, 2003).
Caution and risks interactions
The use of Silver birch, in adequate doses, presents no toxicity or contraindications (essential oil uptake or external application is an exception). The essential oil should not be ingested or used externally because of its highly content of methyl salicylate. Greatly less toxicity is found in birch bark and leaf when in their whole herb formation. The administration in pregnant women, breast-feeding women and children is not recommended (ESCOP, 2003; WebMD).
People who are susceptible to aspirin should not use products prepared from this plant, as it contains considerable quantities of aspirin-like compounds. Individuals with reduced cardiac or kidney function should not use Silver birch products.
Silver birch has been reported to cause skin rashes, similar to the majority of plants, and it may also result in allergic reactions.
Scientists are still studying the safety of betulinic acid (American Cancer Society, 2008).
Interactions (i.e. when using other medications): None known (Williamson and Wren, 2003)
Despite the extensive studies, there is no sufficient evidence for the efficacy and safety of Silver birch products on human health and standardised formulations of Silver birch are not sold in the UK.
Oral formulations of Birch are available in other countries (e.g. German, Austria etc.), standardized according to the European Pharmacopoeia monograph (both Betula pendula and Betula pubescens leaves are included on the drug). (Eur. Ph., 3rd Ed., add. 1998)
The German commission E Monographs approved the use of Betula species for urinary tract infections, kidney and bladder stones, and rheumatism (Bruneton, 1999).
In France the drug is used traditionally to enhance urinary and digestive elimination functions and to increase the renal elimination of water [French Expl. Note, 1998]
However, further studies are needed to find out whether Silver birch is safe and effective for use.
This essay is not intended to advise or recommend herbs for medicinal or health use. This information is for educational purposes only and should not be considered as a recommendation or an endorsement of any particular medical or health treatment. The use of any such product should be based on the appropriate advice of a health care professional or based on the information available in the patient information leaflets (i.e. for THR products). The information provided should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. Please call 999 for all medical emergencies.
© Christina Papazoglou 2015
About the author
Christina Papazoglou is a postgraduate student studying Pharmacognosy at the UCL School of Pharmacy.
Christina Papazoglou MSc student
Research Cluster Biodiversity and Medicines /
Centre for Pharmacognosy and Phytotherapy
UCL School of Pharmacy, Univ. London
29 – 39 Brunswick Sq.
London WC1N 1AX
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Photo: Windswept silver birch tree, Beaulieu Heath, New Forest by Jim Champion. Creative Commons licence – attribution name and URL