Does the Japanese Maple have Medicinal Uses?
Better known as the Japanese Maple (or the smooth Japanese maple, or the palmate maple), Acer palmatum Thunb. was named after a Swedish botanist called Carl Peter Thunberg. He added ‘palmatum’ to the name because he thought the leaves looked like the five fingers of a hand.
Mr. Thunberg may have been the one who officially ‘discovered’ the Japanese maple (in the late eighteenth century), but the Japanese were aware of this species long before that. It has been used in traditional medicine in Japan (and other parts of Asia, Europe, America, and Canada) for thousands of years, but until recently, there have been few scientific studies in Western scientific or medical journals.
This article starts with a general overview of the Japanese maple and its traditional medicinal uses, then focuses on one of the few published articles on the topic.
Properties of Japanese Maples
The genus Aceraceae (or maple) comprises around 129 different species – 99 of which are indigenous to China. The remaining 30 species are also mainly found in the Northern hemisphere – particularly in the temperate parts of East Asia, North America, and Europe.
The Japanese maple is a shrub (or small tree), typically reaching about 6-10m in height, with a dome-shaped crown, and branches appearing low on the trunk. It is indigenous to Japan, China, the Eastern part of Mongolia, North and South Korea, and South-East Russia, but is cultivated around the world on account of its dramatic and attractive leaf colors and shapes.
The hand-shaped leaves are oppositely arranged on the stems, and roughly hand-shaped (that’s where the name palmatum comes from, see above, Introduction). They are usually about 2-5 inches long, and comprise either five or seven lobes. Although the leaves are just a normal green color in summer, they exhibit a wide range of autumn colors, from orange and yellow, through red, to shades of purple.
These dramatic leaf colors and shapes make the Japanese maple especially well-suited to bonsai training.
The Japanese maple has small, inconspicuous flowers, which tend not to attract insects too much. Flowers grow in small clusters called cymes, in which each central stem starts off with a single terminal bud, and the other buds subsequently develop at the ends of additional lateral offshoots of the central stem. Each flower has ten petals: five whitish in color and five reddish or purplish.
However, insects are vital for the pollination of this species. That could be why it is monoecious – that is to say, the male and female flowers grow on the same plant. If the male and female flowers are close together, there would be a better chance that an insect would touch both of them, thus pollinating them.
When the flowers are over, they form a pair of samaras (winged nutlets that can be dispersed easily by the wind). The samaras, which are 2-3 inches in length, support the very small (6-8mm) seed.
Health benefits of Japanese Maples
In addition to its long history of use in traditional medicine, the bark, leaves, and twigs of the Japanese maple have been used since at least the 1700s, normally to treat eye complaints and improve liver function.
Traditional uses, phytochemistry, and pharmacology of the genus Acer (maple): A review
This article, by Wu Bi, Ying Gao, Jie Shen, Chunnian He, Haibo Liu, Yong Peng, Chunong Zhang & Peigen Xiao, was published in 2016 in the Journal of Ethnopharmacology. The authors systematically reviewed literature from books and journals from a number of physical and electronic libraries and databases, published from 1922 to 2015. They also consulted libraries and herbaria both in the USA and in China to find out about the traditional and cultural uses of the Japanese maple.
Most of the article does not refer to the Japanese maple specifically, but rather other species in the maple family. However, the authors note that only a very limited amount of research on the maple genus has been done, and that further studies are needed before anyone can be very confident about the medicinal properties of any of the maple species.
Ironically, the one time the authors do mention Acer palmatum thunb. is when they say that its twigs and leaves are effective for pain relief, combatting free radicals, and treating carbuncles (Bi, 2016:35) – none of which are functions the Japanese maple has traditionally been used for!
2. Traditional uses
As noted, the maple is often used in landscaping because of the dramatic colors and shapes it exhibits. But it is not only good for decorative purposes: maple wood is good for making furniture because it is hard-wearing but not too difficult to carve into different shapes. Maple syrup, which can be made from the sap of several Acer species, has been a popular sweetener (especially in North America and Canada) for centuries.
In traditional medicine in Asia and America, the roots, bark, leaves, fruit, and twigs are all utilized, usually in the form of a tea or edible oil. At the time of writing (2016), the authors said that 331 compounds (extracted from 34 maple species) had been identified that had a number of identifiable biological and pharmacological effects. These effects include antioxidant, anti-inflammatory, and antimicrobial; the extracts also showed signs of being able to provide protection against diabetes and liver disease. (There was no evidence that the extracts helped with eye problems, though.)
In China, around twenty Acer species have been used medicinally for a number of purposes. In North-East Asia, especially Japan and Korea, bark from the stems of Acer species has traditionally been used for liver and eye disorders. Koreans have a history of using Acer species to reduce bleeding from injuries, as well as various liver disorders.
In Canada and the USA, indigenous peoples have been found to use twelve or more Acer species for medicine or food. They have a method of grating the inner bark of some species (not including palmatum) to form fluffy layers, or drying it and pounding it to make flour. Some of the native maples of Canada and America are used against shortness of breath or coughing, eye pain and cataracts – in fact, almost anything, from bronchitis to gonorrhea.
Much less is known about the medicinal uses of the Acer species in Europe, although they are fairly prevalent on the continent.
3. Chemical Constituents
The most abundant chemical compounds in Acer plants are flavonoids and tannins.
Flavonoids are natural substances found in fruit and vegetables, the bark, roots, stems, or flowers of plants, as well as in tea and wine. They can have antioxidant, anti-inflammatory, and anticarcinogenic properties; they can also modulate important enzyme functioning on the cellular level. 62 different flavonoids have been identified in the leaves and/or stems of Acer plants, and, out of all the compounds identified in Acer species, flavonoids account for 18.7%.
Tannins are soluble substances with astringent properties; they are found in many plant tissues, and are responsible for the color and flavor (including astringency) of fruits. Tannins presumably get their name from the fact that they are used for the ‘tanning’ of animal skins (a treatment process to preserve the skins and keep them supple).
They are not normally considered to be desirable in the diet, but they do have antimicrobial effects, which could be beneficial for inhibiting the disproportionate proliferation of microbes in the digestive tract. Ingesting large amounts of tannins would probably be a bad idea, but a small amount – for example, the amount you might get in a tea made from maple leaves – could have health benefits, especially if your digestive microbes are getting out of control.
41 tannins have been identified in the Acer genus (which is just under 12.4% of the total compounds).
4. Pharmacological Action
As I mentioned, the Chinese have been using Acer species for medicinal purposes for thousands of years already, but according to Bi et al., Westernized academic studies on the genus have only really started appearing in the last 10-20 years. The antioxidant and anti-inflammatory properties of Acer species, as well as their efficacy against tumors, have now been quite thoroughly investigated.
In addition, different types of Acer extracts have been shown to kill microbes, as well as to help protect the liver against damage or disease. Finally, different types of Acer extracts stimulate osteoblast differentiation, which is a process involving the osteoblast cells the body needs for building bone.
Acer extracts show antioxidant effects, as do all flavonoids. Antioxidants are found in many fruits and vegetables, and include the vitamins A, C, and E – but to understand the significance of antioxidants, it is necessary to know a bit about free radicals.
Free radicals are naturally-occurring molecules in the body, and, in moderation, can play a part in several important biological functions of the body. They help defend the body against infection, facilitate cellular communication, and are involved in cell division. Free-radicals can also be produced when the body is exposed to too much pollution, or even too much ultraviolet radiation from the sun. Having too many free radicals can be highly detrimental to your health.
Free radicals are highly unstable, owing to their molecular structure. In the outer shell of each free radical, there is one unpaired electron (in contrast to all the other electrons, which pair off two by two). In order to stabilize themselves, free radicals have a strong bias towards ‘stealing’ any unpaired electron from other nearby molecules – and this can be very harmful to cells in the body. Too much damage from free radicals can cause cancer, diabetes, heart disease, and hypertension, in addition to leading to premature aging.
Antioxidants neutralize the unstable free radical molecules. It is relatively easy to get antioxidants from fresh fruit and vegetables in your diet (although not all antioxidants are equally effective). By combatting free radical damage, antioxidants can decrease many signs of aging (including deteriorating vision), improve heart health, and decrease the risk of heart disease, stroke, and cancer.
Anthocyanin and phenolic compounds, both of which are prevalent in Acer extracts, have antioxidant properties, which is why these extracts can combat damage from free radicals.
In a 1971 article in the Journal of Organic Chemistry, Kupchan et al. were the first to show that an extract from the stem and leaves of one of the other maple species (Acer negundo L.) significantly inhibited the growth of cancerous tumors. With respect to a certain type of tumor, the effects of the maple extract seemed powerful enough that the extract was recommended for clinical testing and potential human use.
Bi et al. report that several more recent studies, published between 2006 and 2016, have also found different Acer species to inhibit the growth of some types of cancer cells.
A 2015 study by Ko and Chio found that extracts from some Acer species contained five gallotannins with anti-inflammatory effects. The extracts suppressed the body’s production of nitric oxide, which plays an essential role in all kinds of inflammation. However, like free radicals, too much nitric oxide can be a bad thing. In fact, too much nitric oxide could even be considered the same thing as too many free radicals, because nitric oxide is one of the free radicals found naturally in the body.
Several other studies – mostly involving mice – also showed the anti-inflammatory properties of Acer species.
Extracts from some Acer species (not palmatum, in this case, but see introduction of this section: there has not been enough research done to be very confident about which species have which properties) have also been found to show antibacterial, antifungal, and even antiviral properties. It is possible that those properties might help with eye and liver complaints, just as the Japanese have been claiming for so long.
A number of studies have suggested that Acer species could potentially help with managing type 2 diabetes. This type of diabetes is less severe than type 1 diabetes (which is the type where sufferers have to inject themselves with insulin daily) but can still cause quite severe health complications. Moreover, the number of sufferers of type 2 diabetes is on the rise. Therefore, any natural Acer extracts that have even small normalizing effects on blood sugar could be valuable to many people.
Also on the topic of blood sugar: maple syrup, which can be extracted from several Acer species, is a tasty natural sweetener, which has a lower glycemic index than normal sugar. From a diabetic’s point of view, that’s good news!
Finally, a warning: the samara (seed) and young seedlings of several Acer species have been shown to have bad effects on horses, if they eat them – in North America and Europe, ingesting young plants in this family has quite often proved fatal to horses! So if you have horses, please check that there are no young maples growing in the paddock before you put your precious animals in there!
To reiterate: not much of the research in the article by Bi et al. focused specifically on the Acer palmatum Thunb. Then again, so little modern research has been done into the medicinal properties of this – or any other – maple species that it doesn’t necessarily mean the Japanese maple doesn’t have many medicinal properties. And even if not much modern research has confirmed the efficacy of this species in its traditional medicinal uses, it doesn’t seem wise to ignore the folk wisdom of so many generations of learned Japanese healers.
More research on this question is definitely needed!