Plants and Immunity
By David O’Brien
Plants have a long association with indications such as coughs, colds and supporting immunity. Consequentially many herbal medicinal products on the market contain herbal drugs with traditional uses in relieving coughs, colds and thus improving overall immunity.
In general cough and cold products are either expectorants, antitussives or decongestants/anti-inflammatories. Expectorants seek to remove mucus from the lungs and airways. They primarily do this by increasing the amount of water in the mucus, thus thinning it and allowing you to more easily cough it out. As a result, expectorants often actually increase the amount that you cough. Therefore, many expectorants also lubricate the airways and may act as a relaxant to make each cough more productive and less of an irritant.
Antitussives, on the other hand, aim to reduce coughing. In general, when someone has a mucus cough, the secretion of this mucus and other obstructive material through coughing is to be encouraged. However, it may be that a cough is particularly dry and disrupts sleep or makes the patient.
Decongestants work by shrinking blood vessels in affected areas and decongestion medication tends to contain anti-inflammatory agents. In the case of a cold, by reducing inflammation in the nose, more space is given for air to flow through and for mucus to drain. This should result in increased comfort levels and are used particularly for blocked noses. As can be seen, each of these groups looks to achieve subtly different goals, and this study will examine natural extracts that are suited to each purpose.
We present a select range of herbal drugs targeting relief from symptoms associated with coughs and colds.
WILD CHERRY SYRUP
Wild cherry syrup is a preparation containing an extract from the inner bark of the wild cherry tree, Prunus serotina. The plant is mainly found in Canada and the United States and is a member of the Rosaceae family. It contains volatile compounds known as cyanogenic glycosides as well as phenolics and sugar. Like thyme, wild cherry bark also has an antitussive effect when dealing with dry coughs. In addition to this wild cherry is a mild sedative and has a pleasant taste, enabling it to be used as a natural flavouring agent.
THYME
A common garden herb, Thymus vulgaris is a member of the Labiatae and is often used for cooking. Thyme is characterized by essential oils with thymol being a main constituent. Thyme has a long history of being used in liquid form to thin mucus and relieve congestion. In fact, it has anti-viral, anti-fungal, anti-bacterial properties and can act as an antitussive in the case of dry coughs.
SENEGA
Senega refers to plants from the Polygala genus and are members of the Polygalaceae. The herbal drug is chiefly P. senega which is native to North America and P. tenuifolia which is found in the Far East. It is commonly known by the name snakeroot, rattlesnake root, amongst others. The root is used medicinally due to its antitussive properties which are believed to be associated with the saponin content. Saponins are triterpenoids that form a soap action when mixed with water. Moreover, it has anti-inflammatory properties, helping with swelling of the throat, nose and chest.
IPECACUANHA
The root of Cephaelis ipecacuanha has a long traditional use as an expectorant. Cephaelis ipecacuanha, a member of the Rubiaceae is native to Brazil and the root is known to contain the alkaloids emetine and cephaeline as well as tannins.
LIQUORICE
A well-known flavour, liquorice root (Glycyrrhiza glabra) has expectorant and antitussive properties. The plant has a widespread distribution but is chiefly found in the Mediterranean and Asia. The compound responsible for the sweet taste is glycyrrhizic acid. Glycyrrhizic acid is classified as a saponin. Saponins are known to possess antitussive effects. It also has anti-inflammatory and antioxidant properties. Other compounds present in the root are essential oils and flavonoids.
COCILLANA
Cocillana, also known as Guapi bark refers to the genus Guarea. It is an evergreen tree that is a member of the Meliaceae family and is native to the eastern Andes in South America. The bark is traditionally used as an expectorant. It is known to contain resins, tannins and coumarins.
SQUILL
Squill refers to the genus Drimia and is a member of the Lilly family. Drimia species have a widespread distribution but two species are mainly used in herbal medicine. Drimia Maritima or Mediterranean squill is native to the Mediterranean, particularly southern Italy whilst Drimia indica or Indian squill is native to India. Both contain cardiac glycosides such as bufadienolides and it is the bulb of squill that is used medicinally. When used in moderate doses squill is an effective expectorant (and emetic in larger quantities), however, patients with certain heart, stomach or bowel conditions and pregnant or breast-feeding women should not take squill as the cardiac glycosides may be toxic when taken at higher doses.
MARSHMALLOW ROOT
Also known as Althaea Officinalis, the marshmallow plant is a member of the Malvaceae and is found in Europe, North America and western parts of Asia. As well as being an antitussive, it is also an anti-inflammatory, helping to soothe the throat. The root is known to contain up to 35% mucilage consisting of polysaccharides and is also known to contain flavonoids.
GINGER
Primarily used for its anti-inflammatory and purported anti-bacterial properties, ginger root (Zingiber officinalis) is a member of the Zingiberaceae which has antitussive properties. The plant is distributed across Asia, tropical Africa and the West Indies. It is often combined with honey to balance out its sharp taste and produce a pleasant and effective remedy. Compounds characteristic of ginger root are essential oils and complex molecules known as gingerols and shoagals.
EUPHORBIA
Euphorbia hirta is a member of the Euphorbiaceae family and is commonly known as asthma-weed. It has a widespread distribution. The herb is used medicinally for its pectoral and anti-asthmatic properties. The herb also possesses antibacterial activity. It is known to contain flavonoids and its choline and shikimic acid content may contribute to its medicinal activity.
