degeneration of connective tissue.
Filipendula, or meadowsweet, is a source of tannin and can be used as an astringent in fighting infection.
Flavonoids
Flavonoids and flavonoid glycosides occur widely in nature and impart a yellow, orange and red colour to fruits, vegetables and flowers. With their antioxidant actions, they are an important part of our daily diet, having a beneficial effect on the heart and circulation, strengthening and healing blood vessel walls and enhancing our resilience to stress. They act synergistically with ascorbic acid to enhance the body's ability to metabolise it. Flavonoids are also anti-inflammatory (e.g. quercitrin), hepato-protective (e.g. silymarin and quercitrin), anti-tumour, anti-viral and hypotensive. Herbs rich in flavonoids (e.g. kaempherol, myricitin, quercitrin) protect against cardiovascular disease and are used to treat vascular problems, including for example venous insufficiency, bruising, piles and nose bleeds.
Isoflavones, such as genistein from soya, have a similar structure to oestrogen. They bind to oestrogen receptors in the body and are known as phytoestrogens. They occur in herbs includingare shatavari, wild indigo, liquorice, red clover and black cohosh. They have been found to help prevent tumours and breast cancer, and to relieve menopausal symptoms.
Anthocyanins and anthocyanidins are found in red, blue and black fruits, and particularly found in high amounts in grape skins, elderberries and bilberries. They also occur in herbs, including ginkgo, cat's claw and corn silk. They have antioxidant actions that protect against oxidative damage, particularly in the eyes and connective tissue.
Terpenes
Terpenes, or terpenoids, occur widely in a variety of forms, including monoterpenes, sesquiterpenes and triterpenes.
Monoterpenes are the main components of volatile oils (see next page), and include bitter iridoids, as in the sedative valepotriates in valerian, hypotensive asperulsides in cleavers, and paeoniflorin in peony, which has anti-inflammatory, febrifuge and sedative actions.
Cimicifuga, or black cohosh, contains isoflavones, which have been found to prevent tumours.
Sesquiterpenes are also found in volatile oils or as lactones, and have a bitter taste, anti-inflammatory and antimicrobial actions. Sesquiterpenes are found in myrrh, hops, German chamomile and vitex, and sesquiterpene lactones occur in boneset, feverfew, yarrow, wormwood, globe artichoke and elecampane.
Triterpenes have a similar structure to steroids (see below).
Bitters
Bitter principles is a term for a group of chemicals that have a very bitter taste and a cooling effect. They are diverse in structure but have certain therapeutic actions in common, and include mostly terpenes, flavonoids and some alkaloids. Through their effect on the bitter receptors on the tongue, they promote secretion of digestive enzymes from the stomach and intestines, flow of bile from the liver and release of hormones.
Bitters are prescribed for poor appetite and digestion, gastritis, heartburn, to regulate blood sugar, to relieve allergies and inflammation and to aid convalescence. Many bitter herbs have other actions; some are relaxant or sedative like hops and valerian, others are anti-inflammatory like devil's claw, and some, like marigold, exert a beneficial action on the immune system, acting as natural antibiotics and anti-neoplastics. Well known “bitter tonics” include dandelion, cleavers, blessed thistle, wormwood, dock root and gentian.
Triterpenoids and Saponins
Triterpenoids represent a large and diverse group that includes phytosterols, triterpenoid saponins, steroidal saponins and cardiac glycodises.
The leaves of Cynara scolymus, or globe artichoke, contain sequiterpene actones, which can reduce inflamation and protect against infection.
Phytosterols
Phytosterols such as sitosterol and stigmasterol are vital to the formation of cell membranes and help regulate cholesterol, for example guggulsterones in guggulu which lower cholesterol and triglycerides by their regulatory effect on the thyroid are a good example. Phytosterols have been used as building blocks for making steroid drugs and may have the ability to inhibit tumour formation; withanolides in ashwagandha, for example, have antitumour and hepatoprotective properties (Pengelly, 2004).
Saponins
Saponins are glycosides that form a soap-like lather when they are mixed with water and precipitate cholesterol. Herbs containing saponins have a bitter taste and haemolytic activity. They can dissolve red blood cells walls so should never be injected into the blood stream. Taken orally, however, they are hardly absorbed through an intact intestine and help to promote digestion and absorption, for example of nutrients including calcium and silicon. Some, like horse chestnut, have a beneficial action on blood vessel walls, some decrease blood coagulation, blood sugar and cholesterol levels (Tillotson, 2001). Some, like goldenrod and horsetail, are duiretic. Others like mullein are expectorant, and several have hepato-protective and immuno-modulating effects, for example Korean ginseng and liquorice.
Triterpenoid saponins
These help regulate steroidal hormonal activity and counter the effects of stress, and often have antifungal properties. Herbs containing these hormone-regulating properties are known as adaptogens, the most famous of which is panax ginseng. Others include liquorice, wild yam and fenugreek. Some, like wild yam and liquorice, act as anti-inflammatories.
Solidago virgaurea, or goldenrod, contains saponins, which promote digestion and absorption.
Steroidal saponins
These, such as diosgenin from wild yam, are used in the body as building blocks for the production hormones secreted by the testes, ovaries and adrenal glands, and for vitamin D.
Cardiac glycosides
Discovered in 1785 in foxglove, these have been widely researched for their ability to increase cardiac output by effecting the force and speed of heart contractions, which is beneficial in dealing with heart failure. Herbs containing these are generally for use by practitioners only.
Volatile Oils
The exotic perfumes and delicious tastes of aromatic herbs are derived from volatile oils, which are complex combinations compounds, and the different combinations of these produce the wide variation in scent and therapeutic effects in the herbs containing them. Up to 60 different chemical constituents have been identified in some oils. Categories of volatile oils include terpenoids, including monoterpenes and sesquiterpenes and phenylpropanoids. Herbs rich in volatile oils have to be stored carefully in sealed bottles or containers as volatile oils can evaporate easily.
All volatile oils are antiseptic, stimulating the production of white blood cells and enhancing immunity. Many oils have antibacterial, antifungal and antiviral
