Willow bark: General presentation

What is Willow Bark?

Willow bark has been used traditionally as a medicine for centuries, it is mentioned during the time of Hippocrates around 400 BC, when it was used by people to reduce fevers or inflammation by chewing on the bark. As well as being used in Europe as part of folk medicine, and in the late 1800s, salicin was used to develop aspirin.

Willow bark has also be used as part of traditional medicine in China and other Asian countries for the treatment of pain, headache, and inflammatory conditions, such as bursitis and tendinitis.The earliest recorded use of willow bark for medicinal purposes was 500 BC in China.

White willow bark contains a number of active compounds, with Salicylate derivatives being the primary medicinal constituents. Many plant species contain small amounts of salicin though the inner bark of the willow tree is the most common source for these compounds. Salicin is converted into saligenin in the intestine, this is then absorbed and oxidized making salicylic acid (1).

The active extract of the bark, salicin, is named after the Latin name for the White Willow (Salix alba), and was first isolated in its crystalline form in 1828 by Henri Leroux, a French pharmacist. Then in 1838, Raffaele Piria, an Italian chemist working in Paris, later succeeded in isolating the compound in its pure form. In the year 1899 the modern history of salicylates began when the compound acetylsalicylic acid was registered and introduced commercially as “aspirin” by the Bayer Company in Germany. This led to people turning to aspirin instead of willow bark in the following decades and its use fell into decline.

Salicin, which is a chemical similar to aspirin (acetylsalicylic acid) and whilst generally considered to be the primary active compound, the polyphenols and flavonoids in willow bark have also more recently been the focus of research efforts (2). Naringenin glycosides, oligomeric procyanidins, and condensed tannins, derived from the flavonols present in the bark, have been obtained from the willow. In combination with the plant’s powerful anti-inflammatory plant compounds called flavonoids. So whilst salicin is thought to be responsible for the pain-relieving and anti-inflammatory effects of the herb there is now a renewed interest in willow bark from the research community as it appears these other compounds have effects that commercial aspirin does not.

Sources of Willow Bark

The willows are part of the the genus Salix which has around 400 different species, with most willows being found in temperate or arctic regions. There are even a few species that can be found in subtropical or even tropical regions though the majority favour cooler climes. Geographically the species are native to all continents with the exception of Australia and Antarctica. Traditionally medicinal bark is gathered in early spring from young branches between two or three years old.

The willow family includes a variety of different species of trees and shrubs native to Europe, Asia, and North America. Some of the more well known species are white willow or European willow (Salix alba), black willow or pussy willow (Salix nigra), crack willow (Salix fragilis), purple willow (Salix purpurea), and the weeping willow (Salix babylonica). Willows are dioecious, which means male and female flowers appear as catkins on separate plants. Catkins are produced early in the spring, quite often before the leaves have started to appear.

The staminate (male) flowers are without either a calyx or corolla; they consist simply of stamens, varying between species from two to 10. The Staminate is accompanied by a nectariferous gland inserted on the base of a scale which is itself borne on the rachis of a hanging raceme called a catkin. The scale is square shaped and hairy. The anthers are rose coloured within the bud, but turn orange or purple after the flower opens. Flowers are two-celled in form and the cells open longitudinally, filaments are threadlike, usually pale brown, and often bald.

The pistillate (female) flowers are also without a calyx or corolla, and consist of a single ovary with a small, nectar gland inserted on the base of a scale which is also hangs from the rachis of a catkin. The ovary is one-celled, the style two-lobed, and the are ovules numerous.

However not all willow species reliably accumulate a therapeutically sufficient amount of salicin. The willow bark sold in supplements often includes a combination of the bark from white, purple, and crack willows though single species bark can also be obtained.

Willow Bark Extract

Modern extraction methods allow supplement manufacturers to produce high purity willow bark in a quantity suitable for medicinal use.

During processing of the bark it must be carefully handled as the salicylates in the bark are chemically unstable and are destroyed with exposure to boiling water, in order to preserve these compounds the bark must be carefully dried (3). Quality suppliers of willow bark handle the bark carefully to ensure purity and prepare it in a way that preserves these unstable components. Quality extraction methods, used to avoid decomposition of the native glycosides, have been developed. Willow bark extract is standardized for its salicin content ranging from 15%-50% though 25% is generally the ideal as it has less chance of causing irritation. While the leaves generally contain lower concentrations of salicylates than the bark, several species contain medicinally useful quantities of salicylates in their leaves (4).

All reputable dietary supplement manufacturers clearly describe the method that was employed to isolate and process their products. An extract can be offered in a pure form that contains no additives, or in the form of a compound that includes other active ingredients such as additional vitamins and minerals to create a supplement blend.

Uses of willow bark

The use of willow bark dates back around 6000 years and ancient civilizations used it to treat pain, inflammation and muscular issues. The ancient Egyptians used willow for treating joint pain and inflammation. Ancient Assyrian clay tablets discovered by archaeologists also suggest they used willow extracts for the same thing and also for treating fevers.

The Chinese also have used willow in traditional folk medicine for treating fever, pain, colds and as an antiseptic. The ancient Greeks also used willow, including the physician Dioscorides who prescribed willow the for analgesic and anti-inflammatory properties (5-6). Willow bark was also used by Native American healers in North America.

In Europe near the end of the 19th century, salicylic acid was commonly used instead of willow bark and its derivative aspirin. This was due to it being less irritating to the mouth and stomach (7). However the disadvantage is that salicylic acid and aspirin do not contain the other active ingredients that willow bark does such as the flavonols and polyphenols. Prior to this, remedies made from willow bark had been used to treat fever and rheumatic complaints from at least 1763, when Edward Stone described their efficacy against malaria fever.

It is likely it was used in folk medicine before this and there are references to it being used in St Paul’s potion. The list of ingredients included liquorice, sage, willow, roses, fennel, cinnamon, ginger, cloves, cormorant blood, mandrake, dragon’s blood (red resin of the tree Dracaena draco) and three kinds of pepper. The resulting potion was for treating epilepsy, catalepsy and stomach problems. Whilst the list of ingredients may seem bizarre some of them do have medicinal properties.

Willow bark research

Willow bark has documented anticancer properties, the mechanism of action might be associated with growth inhibition and resulting in apoptosis, DNA, damage to the cell membranes or damage to the proteins in the cancer cell (8-9).

Supplementing with willow bark has been shown to relieve headaches and there is some evidence to suggest and it more gentle and less likely to cause gastrointestinal side effects than other pain relievers, such as ibuprofen and other nonsteroidal anti-inflammatory drugs. Willow appears to bring pain relief more slowly compared to aspirin, but its effects may last longer.

In a 2007 study the leaves from Salix.safsaf were shown to inhibit the growth of acute myeloid leukemia cells (10). Willow bark extract has also shown utility in inhibiting the growth of tumours of human colon and lung cancer cell lines (11). Another study found that willow extract destroyed between 75% to 80% of abnormal cells harvested from seven patients with acute lymphoblastic leukemia and thirteen patients with acute myeloid leukemia (12).

Willow bark was also tested for its anticancer and antiproliferative properties on colon-carcinoma cell line HT-29 and was found to have anti-proliferative and pro-apoptotic effects similar to NSAIDs (13).

Willow bark was tested in rats to demonstrate that it was equally effective as acetylsalicylic acid in reducing various inflammatory biomarkers (14). A 2010 in vitro study on human monocytes and differentiated macrophages showed willow bark extract also had an anti-inflammatory action when tested (15).

Due to its astringent, anti-inflammatory, and soothing properties willow bark extract can be found in a number of cosmetic products as well as salicylic acid which is used in a number of acne treatments as it helps skin by helping to shed dead skin cells and clearing pores. Willow bark also contains phenolic acids such as, salicin, salicortin and flavonoids, tannins, and minerals, which help with skin rejuvenation.

A 1991 study published in the journal clinical therapeutics sounds that mild to moderate acne could be improved by treatment with salicylic acid. Salicylic acid was able to reduce the number of primary lesions reducing the severity of acne (16).

A study in 2001 found that in a group of almost two hundred people with lower back pain, those who supplemented with willow bark showed a significant improvement in pain compared to the placebo group (17). The study also showed that willow bark was also more effective in a dose dependent manner with the 240 mg group experiencing better pain relief than those taking 120 mg.

How To Take Willow Bark?

The use of an extract of willow bark acid as an accompaniment to food should not cause any health related side effects if the prescribed doses and treatment instructions are strictly observed. Any side effects tend to be mild. However, stomach upset, ulcers, nausea, vomiting, and stomach bleeding are potential side effects of all compounds containing salicylates. If you experience any such side effects cease taking willow bark immediately and consult your physician.

As applies to taking any supplements patients using medication are advised to consult their physician prior to taking extract of willow bark. Salicylates are not recommended during pregnancy, so pregnant and breastfeeding women should not take willow bark. Due to the danger of developing Reye syndrome (a rare but serious illness associated with the use of aspirin in children), children and those under the age of eighteen should not use willow bark.

Purchasing a standardized willow bark extract with a purity rating of higher than 90% is the best way to maximize the benefits of willow bark acid while eliminating any undesirable side effects. All quality nutritional supplements are subjected to laboratory analysis and strict quality control standards. There is no substitute for quality when it comes to purchasing supplements so always ensure you buy the best quality products. Always purchase your nutritional supplements from a trusted vendor that thoroughly researches every product that they recommend to their customers.

References
(1) Meier, B., Sticher, O., & Julkunen-Tiitto, R. (1988). Pharmaceutical aspects of the use of willows in herbal remedies. Planta Medica, 54(06), 559-560.
(2) Nahrstedt, A., Schmidt, M., Jäggi, R., Metz, J., & Khayyal, M. T. (2007). Willow bark extract: the contribution of polyphenols to the overall effect. Wiener Medizinische Wochenschrift, 157(13-14), 348-351.
(3) Julkunen-Tiitto, R., & Tahvanainen, J. (1989). The effect of the sample preparation method of extractable phenolics of Salicaceae species. Planta medica, 55(01), 55-58.
(4) Julkunen-Tiitto, R. (1986). A chemotaxonomic survey of phenolics in leaves of northern Salicaceae species. Phytochemistry, 25(3), 663-667.
(5) Mahdi JG , Mahdi AJ , Mahdi AJ , Bowen ID . The historical analysis of aspirin discovery, its relation to the willow tree and antiproliferative and anticancer potential . Cell Prolif . 2006 ; 39 ( 2 ): 147-155 .
(6) Hedner T , Everts B . The early clinical history o f salicylates in rheumatology and pain . Clin Rheumatol . 1998 ; 17 ( 1 ): 17-25 .
(7) Jourdier, S. (1999). A miracle drug. Chemistry in Britain, 35(2), 33-35.
(8) El-Shemy, H. A., Aboul-Enein, A. M., Aboul-Enein, M. I., Issa, S. I., & Fujita, K. (2003). The effect of willow leaf extracts on human leukemic cells in vitro. BMB Reports, 36(4), 387-389.
(9) El-Shemy, H. A., Aboul-Enein, A. M., Aboul-Enein, K. M., & Fujita, K. (2007). Willow leaves’ extracts contain anti-tumor agents effective against three cell types. Plos one, 2(1), e178.
(10) Hostanska, K., Jürgenliemk, G., Abel, G., Nahrstedt, A., & Saller, R. (2007). Willow bark extract (BNO1455) and its fractions suppress growth and induce apoptosis in human colon and lung cancer cells. Cancer detection and prevention, 31(2), 129-139.
(11) El-Shemy, H. A., Aboul-Enein, A. M., Aboul-Enein, K. M., & Fujita, K. (2007). Willow leaves’ extracts contain anti-tumor agents effective against three cell types. Plos one, 2(1), e178.
(12) El-Shemy, H. A., Aboul-Enein, A. M., Aboul-Enein, M. I., Issa, S. I., & Fujita, K. (2003). The effect of willow leaf extracts on human leukemic cells in vitro. BMB Reports, 36(4), 387-389.
(13) Bonaterra, G. A., Kelber, O., Weiser, D., Metz, J., & Kinscherf, R. (2010). In vitro anti-proliferative effects of the willow bark extract STW 33-I. Arzneimittelforschung, 60(06), 330-335.
(14) Kähkönen, M. P., Hopia, A. I., Vuorela, H. J., Rauha, J. P., Pihlaja, K., Kujala, T. S., & Heinonen, M. (1999). Antioxidant activity of plant extracts containing phenolic compounds. Journal of agricultural and food chemistry, 47(10), 3954-3962.
(15) Bonaterra, G. A., Heinrich, E. U., Kelber, O., Weiser, D., Metz, J., & Kinscherf, R. (2010). Anti-inflammatory effects of the willow bark extract STW 33-I (Proaktiv®) in LPS-activated human monocytes and differentiated macrophages. Phytomedicine, 17(14), 1106-1113.
(16) Zander, E., & Weisman, S. (1991). Treatment of acne vulgaris with salicylic acid pads. Clinical therapeutics, 14(2), 247-253.
(17) Chrubasik, S., Künzel, O., Model, A., Conradt, C., & Black, A. (2001). Treatment of low back pain with a herbal or synthetic anti‐rheumatic: a randomized controlled study. Willow bark extract for low back pain. Rheumatology, 40(12), 1388-1393.