The Pharmaceutical Journal
Vol 277 No 7483 p719-721
22/29 December 2007

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Oh Christmas tree, oh Christmas tree

Pharmacist Sarah Marshall looks at the medicinal uses of Christmas trees

Christmas miscellany 2007 index

To many of us a decorated evergreen tree is an essential ingredient in the Christmas festivities. There is uncertainty, however, as to how and when the custom began.

Many ancient cultures, including the Chinese, Egyptians and Romans, brought evergreens into the home as a reminder of the spring to come. The tradition of the modern day Christmas tree however, appears to have begun in Western Germany.

In the 14th and 15th centuries evergreen boughs, hung with apples, were used to illustrate plays about Adam and Eve — a means of teaching the Bible to an illiterate population. This “paradise tree” was subsequently brought into German homes on 24 December (the feast day of Adam and Eve). Candles were also added.

Households would also have a “Christmas pyramid”, a triangular set of shelves used to hold Christmas figurines and decorated with evergreen cuttings, candles and a star. By the 16th century the paradise tree and the pyramid had merged, to become the Christmas tree.

There are other early reports of Christmas trees. For example, Latvia claims to be the home of the first decorated Christmas tree, documented in 1510.

Legend also has it that Martin Luther played a role in the Christmas tree tradition at about the same time. Inspired by a night-time walk in a forest he brought a tree into the house and covered it with candles to try to recreate for his children the magical effect of moon and stars shining through evergreen foliage.

What is clear is that by the 18th century the custom had become widespread in Germany. Early decorations included gingerbread, barley sugar twists and multicoloured flowers made of paper, apples and gilded nuts. Tinsel was invented in 1610 and was originally made from strips of real silver.

Although often credited to Prince Albert, it was Queen Charlotte (Queen Victoria’s grandmother) who brought the first Christmas tree to Britain from Germany. Such trees were a central part of Princess Victoria’s childhood Christmases. Subsequently, Queen Victoria and Prince Albert encouraged German Christmas traditions with the prince himself decorating the tree with sweets, wax dolls, strings of almonds and raisins and candles.

In 1846, the royal couple were pictured in the Illustrated London News with their children around a Christmas tree, and Victoria’s popularity meant that the custom became fashionable in Britain and the US.

Victorian trees originally stood on top of a table, but by the 1880s they were so huge that they had to be placed upon the floor. Trees were decorated with hand-blown glass ornaments and glass bead garlands made in Germany. By 1890, in the US, a F. W. Woolworth was selling US$25m worth of ornaments annually, including strings of electric lights.

With Victoria’s death in 1901 trees lapsed from fashion, only re-emerging in the 1930s. In post-war Britain, artificial trees became popular, made of green-dyed goose feathers. The Addis brush company, with the machinery it used to make its toilet brushes, created the first brush trees with green plastic bristles. In the 1960s designer trees made of aluminium were popular. Now however, live trees are back in fashion.

All the species of evergreen used as Christmas trees are coniferous. Conifers grow all over the globe from within the Arctic circle to the furthermost limits of tree growth in the southern hemisphere. They are most abundant in cool, temperate and boreal regions but also occur in tropical areas.

Their abundance means they contribute greatly to the biosphere through photosynthesis. Even trees grown commercially can be beneficial: it has been claimed that every acre of Christmas tree plantation provides enough oxygen for 18 people daily.

Conifers are a varied group, with several record-breaking members. The world’s oldest trees are the 4,900-year-old bristlecone pines (Pinus longaeva) of the desert mountains in California and Nevada. The largest known trees are the giant sequoias (Sequoiadendron giganteum) reaching heights of more than 95 metres and weighing at least two million kilograms. They are found in the Sierra Nevada of California.

The tallest trees are the redwoods (Sequoia sempervirens) in coastal California, which may be more than 110m tall. Ironically, adjacent to these redwood forests, grow some of the world’s smallest trees, also conifers. The sterility of the soil in those parts means that trees such as the bonsai cypress (Cupressus goveniana) and the shore pines (Pinus contorta) reach full height at less than 20cm whereas in a fertile soil they would 30m or more.

Conifers used as Christmas trees are all members of the Pinaceae family, which has 10–12 genera and about 200 species. This pine family comprises predominantly trees; most are evergreen with needle-like leaves. Genera in this family include the fir (Abies), Douglas fir (Pseudotsuga), hemlock (Tsuga), larch (Larix), cedar (Cedrus), pine (Pinus) and spruce (Picea).

The generic name Picea is derived from the Latin pix, alluding to the pitch or resin that some species produce. Members of the pine family are used extensively in timber and paper making industries, but they are also sources of oils, resins, foods (eg, pine nuts) and flavouring for beverages (eg, juniper berries to flavour gin) and, of course, pharmaceuticals.

Cultivation

Until 30 years ago, Christmas trees were a by-product of forestry for raw materials, a use for trees which had been thinned out from plantations. Now some 15,000 hectares is given over to specialist Christmas tree cultivation in the UK.

Many different species of tree are sold as Christmas trees, including Nordman fir (Abies nordmanniana), Norway spruce (Picea abies), Noble Fir (Abies procera), Lodgepole pine (Pinus contorta var. latifolia), Scots pine (Pinus sylvestris), Serbian Spruce (Picea omorika), Blue spruce (Picea pungens glauca) and the Fraser fir (Abies fraseri).

In the UK some eight million trees are sold annually, with the Nordman fir taking about 60 per cent of the market, followed by the Norway spruce. The Nordman fir is native to south Russia, but has become increasingly popular as a Christmas tree, because it retains its needles. The Norway spruce, the traditional Christmas tree, has pointed rich green needles, which drop readily.

The Nordman fir was introduced into Britain in 1848. The trees are grown in Scotland and Denmark from seed harvested in Georgia, Russia, which is sown in sandy nursery beds. Once three years old, the trees are transplanted to a plantation where they remain until ready for harvesting, up to 12 years later.

During growth they are fertilised regularly, protected from wind and frost — a single late spring frost or pest outbreak can result in a worthless crop — and treated to prevent disease and insect damage. They are also pruned by hand with shears to ensure the compact conical form favoured by customers.

Trees are harvested in November with chain saws and lower branches are removed, allowing more room for presents underneath. They are then netted and transported. Some trees are sold live with roots and soil, to be planted outdoors after the Christmas festivities. The survival rate of these trees is low however, due to the combination of root damage during digging and high temperatures and low humidity indoors. Typically, a 6ft Nordmann fir would be 10 years old.

Pharmaceutical uses of Pinaceae

Members of the Pinaceae family produce a number of pharmaceutically useful products, such as turpentine, oil of turpentine, rosin (or colophony) and wood tars, as well as essential oils. Although their use is waning, many are still included in the British Pharmacopoiea.

Turpentines Turpentines are oleoresins and are semi-fluid substances derived from Pinus (including P pinaster and P sylvestris) and other conifers. They consist of resins dissolved in volatile oil and are obtained from living tissue by making a longitudinal cut in the tree trunk and attaching a cup to capture the exudate resulting from the injury.

Trees may be tapped for 40 years in this way, gradually increasing the length of the cut. The resinous mixture collected is separated by steam distillation into a volatile oil and a non-volatile portion called rosin.

The volatile oil is then rectified (ie, treated with aqueous alkali and redistilled to remove traces of phenols, cresols, resin acid etc) to purify it, yielding a colourless liquid with a characteristic odour and pungent taste, known as oil of turpentine.

Oil of turpentine Oil of turpentine consists primarily of the terpenes (+)- and (–)-alpha-pinene, (–)-beta-pinene and camphene, but also beta-phellandrene, delta-3-carene, limonene, p-cymene, longifoline, and estragol. It is used as a counter irritant and rubefacient, and is an ingredient in White Liniment BP and other embrocations for muscular aches. It is also used in aromatic rubs to treat nasal congestion, although the safety and efficacy of oil of turpentine for respiratory tract disorders has been questioned.

Oil of turpentine is widely used as a solvent and was formerly used to dissolve paint and varnish. However, currently its greatest role is as a raw material for perfume, flavourings, vitamins, resins, insecticides, synthetic pine oil and camphor. It is also used as rubber solvent in the manufacture of plastics.

Turpentine oil poisoning can be fatal and symptoms include gastrointestinal upset, local burning, coughing and choking, pulmonary oedema, excitement, coma, fever, tachycardia, liver damage, haematuria and albuminuria.

Colophony Colophony or rosin is the resin remaining after distillation of the oleoresin. It forms translucent, pale yellow to brown-yellow irregular shaped brittle, glassy pieces of different sizes. It is an ingredient of Flexible Collodion BP and is used in ointments and dressings to seal minor wounds and cuts as well to treat minor skin disorders, however skin sensitisation has been reported.

Colophony contains resin acids (90 per cent), neutral inert substances formerly known as resenes and esters of fatty acids. Resin acids are isomeric diterpene acids, and include (+)-pimaric acid and abietic acid. They demonstrate antimicrobial, antiulcer and cardiovascular activities.

Non medicinal uses of rosin and its derivatives include manufacture of soaps, varnishes, sealing wax, printing inks, adhesives, gloss oils for paints and pitch for casks. Rosin is also used on the shoes of ballet-dancers, floors of studios and stages to prevent slipping and to treat the bows of stringed instruments.

Wood tar Destructive distillation (rather than tapping) of stumps and roots of various trees of the family Pinaceae produces a type of wood tar known commercially as Stockholm tar. This is a black semi-liquid, with a characteristic odour and taste. It comprises a complex mixture of ingredients, such as phenols and phenolic ethers, hydrocarbons (including benzene and toluene) and paraffins.

Wood tar has been used externally as an ointment, for its antipruritic and antiseptic action in skin disorders, such as eczema. However, it has largely been replaced by the use of coal tars, since tars derived from wood are more likely to cause sensitisation. Distillation of wood tar produces creosote. This has been used for its reputed expectorant properties.

Pine silvestris oil Some of the coniferous species used as Christmas trees, for example Scots pine (Pinus sylvestris L) and the Norway spruce (Picea abies) have other pharmaceutical uses. Steam distillation of needles or tips of Pinus sylvestris grown in the US or Hungary generates a volatile oil known as pine silvestris oil. It is a clear colourless or pale yellow essential oil with a characteristic odour. It is used in aromatherapy for a wide variety of conditions, and also as a herbal ingredient in over-the-counter medicines for coughs, colds and catarrh (eg, Karvol).

Pine silvestris oil is also used as rubefacient to relieve muscle aches and rheumatism. Major components include the monoterpenes alpha-pinene, beta-pinene and limonene, as well as myrcene and bornyl acetate. Minor components include the monoterpenes alpha-terpineol, p-cymene, delta-3-carene, terpinolene, camphene, and 1,8-cineole, and the sesquiterpenes caryophyllene, gamma-cadinene, and muurolene.

Sensitisation reactions, such as dermatitis, or eczema-like reactions can occur particularly if the oil is high in delta-3-carene, contains eugenol or alpha-phellandrene or is oxidised. Thus oils used on the skin in aromatherapy should be fresh.

In vitro tests have shown pine silvestris oil to have some antibacterial and antifungal activity as well as genotoxicity. Antiviral and antibacterial activity has been attributed to the limonene, dipentene and bornyl acetate content. alpha-Pinene has been shown to have antioxidant activity. In vivo experiments have indicated that pine oil may potently modulate bone metabolism. Oil derived from various species of pine, including P sylvestris, is in perfumes and household fragrances and cleaning products.

Novel uses

One of the latest pharmaceutical uses for Christmas trees is in trying to ensure a plentiful supply of antiviral drugs against bird flu. Infection of humans with avian influenza virus H5N1 was first reported in 1997, initially in Hong Kong.

A decade later more than 330 people have been infected with H5N1 avian influenza worldwide, largely via exposure to sick birds, and almost two thirds of those contracting the disease have died. Only limited human-to-human transmission has as yet been reported but there are fears that mutation of the virus could lead to a more easily transmissible form and thus a worldwide pandemic.

The antiviral oseltamivir (Tamiflu; Roche) acts by inhibiting the enzyme neuraminidase, thereby preventing the release of virus particles from infected cells. It is active against influenza A and B viral neuraminidase. The World Health Organization has recommended that oseltamivir should be stockpiled in case an avian influenza pandemic should strike.

However the synthesis of oseltamivir is a complex and expensive multi-step process, which uses shikimic acid as a starting material. Shikimic acid is an important biosynthetic intermediate in many plants and micro-organisms. Roche extracts it from seeds of Chinese star anise (Illicium verum), an evergreen tree about 4 or 5m in height, indigenous to the south west provinces of China.

However, the yield of shikimic acid from the seeds can be low — extraction of 30kg of star anise provides a mere 1kg of shikimic acid, leading Roche to declare a shortage of shikimic acid in 2005 and sending the price of the raw material up to $1,000 per kg.

In order to overcome the vulnerability of the supply from this seasonal plant, alternative methods for producing shikimic acid are being investigated. Recently, fermentation methods to produce shikimic acid using genetically modified Escherichia coli have been developed and now account for one third of Roche’s production.

A Canadian company, Biolyse Pharma Corporation, came up with an innovative solution to a potential shortage of shikimic acid: that of using recycled Christmas trees. The needles of discarded pine, fir and spruces are a source of the biosynthetic intermediate, with up to 2–3 per cent of the biomass of typical Christmas trees being extractable shikimic acid.

At the start of 2006, some 500,000 trees were donated by Toronto residents. The needles were dried and powdered and are being stored at present because, ironically, by December 2006 the price of shikimic acid had plummeted to $50 per kg, making it cheaper to buy than extract. The fall may have been because fears regarding bird flu have lessened or because the surfeit of shikimic acid held by Biolyse has influenced the market. Biolyse has stated that in the event of a pandemic it could manufacture a million oseltamivir tablets daily.

Christmas trees have, for centuries, been a symbol of light in the darkness, joy in the depths of midwinter and the hope of new life. Let us hope that we have no need of their use in pandemic influenza measures, now or in the future.

ACKNOWLEDGEMENT I thank Roger Hay of the British Christmas Tree Growers Association for providing information regarding the cultivation of Christmas trees in the UK.