Bij de yamswortelfamilie (Dioscoreacea), die in totaal zo'n 600 soorten kent, neemt het geslacht Dioscorea veruit de belangrijkste plaats in. De tien overige geslachten herbergen alles bijeen niet meer dan 35 soorten. In onze streken heeft de familie slechts één vertegenwoordiger, de spekwortel (Tamus communis), die in België wel groeit in beukenbossen en onder hagen.
De familie is vooral bekend om de vele soorten yams: de eetbare knollen van deze tropische slingerplanten, die vaak zowel onder als boven de grond worden gevormd. Het totale oppervlak aan yamteelt in de wereld bedraagt ongeveer 2,5 miljoen ha, waarvan alleen al 2,3 miljoen ha in Afrika. Midden-Amerika (55.000 ha), Zuid-Amerika (40.000 ha) en Azië (16.000 ha) blijven daar ver bij achter. De yams zijn oorspronkelijk afkomstig uit Afrika en Azië, maar zijn inmiddels over de gehele tropengordel verspreid, tot op de eilanden in de Grote Oceaan. Zelfs in het zuiden van de Verenigde Staten worden yams verbouwd, als is de teelt daar van weinig betekenis.
Dioscorea alata Engels: Greater yam, water -am, winged yam Frans : Igname de Chine Duits: Yam Wurzel, Was-seryam
Omschrijving: Gelobde of vertakte, vlezige knollen, die sterk in vorm kunnen verschillen en wel wat lijken op een dahliaknol. Oorsprong: Zuidoost-Azië.
Produktie: India, Filippijnen, Polynésie.
Aanvoer: Het gehele jaar, zij het beperkt. Gebruik: Rauw in salades of, in schijven gesneden, bakken in olie. Houdbaarheid: Tamelijk kort; gevoelig voor lage-temperatuurbederf. Voedingswaarde: Per ioo g: 23 g koolhydraten; 2,0 g eiwit; 0,2 g vet; 10 mg calcium;
0,3 mg ijzer; 10 mg vitamine C.
Deze soort krijgen we hier zelden of nooit te zien. De verwarring wordt nog vergroot doordat sommige zoete aardappelsoorten (Ipomoea sp) ook wel eens onder de naam ' worden aangevoerd - of omgekeerd. De belangrijkste soorten voor de Westeuropese markt zijn de yam en twee soorten die bekend zijn onder de naam aardappelyam. Van een van deze laatste, D. batatas, krijgt de amateurtuinder wel eens kleine plantknollen aangeboden die 'Igname de Chine' worden genoemd. Half mei geplant (in de warme kas) leveren ze omstreeks november langwerpige knollen van zo'n 40 cm lengte. Ze kunnen worden bewaard als aardappelen. Dit laatste geldt waarschijnlijk ook voor yams die op de markt of in de winkel worden gekocht. Yamsoorten die hier incidenteel wel eens worden aangevoerd zijn D. cayennensis (yellowyam, twelve-month yam, eut yam, come yam) uit West-Afrika en Centraal Amerika, D. esculenta (lesser yam, Asiate yam, potato yam, Chinese yam) uit India en Maleisië, D. rotundata (whiteyam, Guineayam, eboeyam) uit West-Afrika en D. dumentorum (bitteryam, cluster yam) uit Midden-Afrika.
Aardappelyam (Dioscorea batatas) Engels : Chinese yam Frans : Igname de Chine Duits : Kartoffelyam, Brot-würzel
Omschrijving: Langwerpige, blanke knollen, ongeveer 40 cm lang. Oorsprong: China. Produktie: China, Korea, Japan, Taiwan Aanvoer: November tot april.
Gebruik: In schijfjes snijden en bakken in olie. Houdbaarheid: Enige maanden op een droge, koele plaats (niet in koelkast). Voedingswaarde: Per 100g: 560kJ/131 kcal; 32,4 g koolhydraten; 2,0 g eiwit; 0,2 g vet; 10 mg calcium; 0,3 mg ijzer; 10 mg vitamine C.
Industriële verwerking: Geen.
Aardappelyam (Diocorea bulbifera) Engels : Potato yam, aerial yam
Frans : Igname Duits: Kartoffelyam Omschrijving: Bol- of waaiervormig gelobde knollen met een roodbruine huid en wit vruchtvlees, dat na het koken tot vuilgroen/geel verkleurt, papperig week van substantie is en enigszins bitter smaakt. Rijpe knollen zijn het beste van smaak. Oorsprong: Tropisch Afrika en Azië. Produktie: Filippijnen, Maleisië.
Aanvoer: Sporadisch. Gebruik: Schillen, in stukken snijden en koken in (kalk) water. Houdbaarheid: Enige maanden op droge, koele plaats (niet in koelkast). Voedingswaarde: Per 100 g: 560 kJ7131 kcal; 32,4 g koolhydraten; 2,0 g eiwit; 0,2 g vet; 10 mg calcium; 0,3 mg ijzer; 10 mg vitamine C.
DIOSCOREA SPP Dioscoreaceae)
Part used Dried underground parts (root and rhizome)1
Summary of usage
Antispasmodic2
Antirheumatic2
Anti-inflammatory3,4
Cholagogue3,5
Stomachic6
Phyto-oestrogen (containing steroidal saponins)2,6
Nervine6
Diaphoretic2,6
Diuretic2
Names used
There is over 600 species in the Dioscorea genus, including some yams that are edible. Amongst the medicinal yams, Dioscorea villosa and occasionally hirticaulis are mentioned in English pharmacopoeias7; Dioscorea villosa, spiculiflora and floribunda in the American6; Dioscorea opposita (batatas) in Chinese2, and Dioscorea japonica in Japanese8 texts. All of these Dioscorea spp. have similar indications, but those species used as part of Traditional Chinese Medicine have additional actions (see below).
Dioscorea transversa (punctata) is an Australian member of Dioscorea spp, which has been used topically for skin cancer.9
• Wild Yam, Colic Root, Rheumatism Root
General description
• Perennial slender twining vine with thin woolly reddish-brown stems
• Leaves are symmetrical and heart-shaped
• Flowers are insignificant and greenish-white or greenish-yellow with panicles.
• The rhizomes are long, knotted, tuberous and woody. They are crooked and laterally branched10
with stem scars, and are tough and yellowish.11
• The cut rhizome consists of irregular, yellow hard woody chips, up to 1 x 3 cm with fine strands
of fibrous roots present.1
• Taste is insipid, bitter and acrid with no odour present.12,13
Known active constituents
Steroidal saponins
• Dioscorea spp. contain a number of saponin glycosides, namely dioscin, botogenin, trillin14, diodenin and dioscorin.3,15
• The wild growing Mexican Yams, Dioscorea floribunda and D. composita are believed to yieldthe most diosgenin and are used for commercial purposes.16
Phytosterols
• â-sitosterol, stigmasterol, taraxerol.7
Alkaloids
• Dioscorine17
Tannins
Starches
History and traditional use
• Used in Mexico since Aztec times, as a treatment for rheumatic complaints and as an analgesic and also in Central America to relieve menstrual, ovarian and labour pains.2
• Traditionally used for bilious colic and nausea of pregnancy, and for spasmodic conditions such as cramps, coughs and hiccoughs.18
• The herb was referred to as a general relaxant by the Physiomedicalists who claimed that it relaxed the autonomic nervous system leading to beneficial effects in the gut.19 The alkaloids are said to be the active constituent responsible for this action.6
• The steroidal saponins were the original source of dioscin used to produce the oral contraceptive pill and other steroid hormones.2
Known pharmacology
The saponin glycosides are considered to be amongst the most active constituents. They are commonly used as fish poisons and can cause haemolysis when injected intravenously, but do not pass through the gut wall, being too large to do so. Once ingested, the normal gut bacteria cleave the glucose molecule, leaving the sapogenin (aglycone), diosgenin that is absorbed.
Diosgenin is also extracted from the plant material as a commercial process for the manufacturing of steroid hormones. One method is to treat the yam with a mineral acid to hydrolyse the glycosides and then filter the remaining matter. The soluble fraction is then neutralised, washed and treated with an apolar solvent (eg. petroleum ether or toluene) which extracts the diosgenin.20
Animal Studies on Constituents
• Anti-cholesterolaemic effects
Saponins and sapogenins, including diosgenin, obtained by extraction from plants and vegetables are useful for the treatment of hypercholesterolaemia. An extract of fenugreek seeds containing > 95% steroidal saponins reduced the total plasma cholesterol of rats by 18-22% without effecting plasma triglycerides.21 Both fenugreek and Diosgenin spp. yield diosgenin. A study involving cats demonstrated that the oral administration of the total saponins of Dioscorea caucasia, at doses of 5-10 mg/kg for 15-20 days, could reduce the plasma cholesterol levels from
360-500 mg % to 50-90 mg %.22
Another study involving rats with experimental atherosclerosis showed that IV injection of the total saponins of Dioscorea nipponica decreased cholesterol as well as reduced lipid infiltration into the aortic wall and cornea.23 Biliary cholesterol output of rats fed diosgenin over 5 days was stimulated over 3-fold, whereas biliary outputs of phospholipids and bile salts were not changed.31 Although an anticholesterolaemic effect has been demonstrated for saponins and sapogenins, this has not been a traditional use of Dioscorea spp in Western herbal medicine. Other plants yielding diosgenin are used however, for example, Trigonella foenum graecum – fenugreek.4 Both Dioscorea caucasia and nipponica are used in Traditional Chinese medicine (TCM).
• Oestrogenic Effects
Diosgenin was given to ovariectomised mice at 20 & 40 mg/kg daily for 15 days. The diosgenin stimulated the growth of mammary epithelium as shown by an increase in DNA content, number of ducts and the appearance of terminal endbuds. Concomitant treatment with oestrogen and diosgenin showed augmentation of the oestrogenic effect of diosgenin especially at the higher dose.
Diosgenin, showed a lack of progesterogenic activity as shown by the absence of alveolar development even in the presence of exogenous oestrogen.24
• Antiphlogistic Action
Saponins and sapogenins were tested for anti-inflammatory effects in rats and mice at a rate of 10 mg/kg using exudative and proliferative models. The strongest antiphlogistic effect was seen amongst the furostanic group of saponins (which yield diosgenin).25
• Experimental Cholangitis
No liver damage occurred in 21 lambs dosed intra-ruminally with up to 9 g of sarsasopogenin or diosgenin daily for 10 consecutive days. No sapogenins were detected in the urine. The results suggest that orally administered sarsasapogenin and diosgenin are either not hepatoxic per se or are too poorly absorbed to elicit a toxic response.26
Clinical Studies
• Progesterogenic Effects
In a non-controlled study, oral and dermal administration of a number of herbs including Dioscorea spp. were examined for their combined effect on progesterone levels. The blood progesterone of the author (post-menopausal woman) showed that none of the herbs were able to alter levels of progesterone after two weeks of ingestion.27 A salivary analysis of progesterone levels was performed on women using wild yam creams and
compared to that of non-users. No differences in salivary progesterone were found.28
A study examining the oestrogen and progestin bioactivity of foods and herbs found that diosgenin from Mexican Wild Yam appeared to suppress progesterone synthesis as determined by RIA (salivary assays). The saliva in all of the women taking the diosgenin containing products contained
very low levels of progesterone. Despite this the researchers did find high levels of progesteronebinding components in 20-30% of the women examined. The authors concluded that this study thus supports the argument that diosgenin is not converted to progesterone in the human body.29
• Antioxidant Action and DHEA Modulation
The antioxidant activity of Dioscorea (a yam steroid extract) and dehydroepiandrosterone (DHEA) was examined amongst volunteers aged between 65 and 82 years. The study was also designed to determine whether Dioscorea supplementation increased serum dihydroepiandrosterone sulphate (DHEAS) levels in humans and modulate lipid levels in older people. Three weeks of supplementation with Dioscorea had no effect on serum DHEAS levels, however supplements of DHEA 85 mg/day increased serum DHEA by 100.3%. Both DHEA and Dioscorea significantly reduced lipid peroxidation, lowered serum triglycerides, phospholipid and increased HDL cholesterol levels, demonstrating that both agents possess significant antioxidant properties.30
Traditional Chinese Medicine15
• An antitussive action is reported for Dioscorea nipponica.
• A series of studies examined the efficacy of a Dioscorea nipponica preparation (Chuanlong
Guanxinning.) on 485 patients suffering from coronary disease. Remission rates were on average 92% for angina pectoris and ECG improvement rates at rest were approximately 40% and after exercise approximately 65%. Reduction in cholesterol levels and triglycerides were also noted along with a lowering of blood pressure in 69% of hypertensive patients.
• Two hundred cases of cerebral arteriosclerosis of 2-15 years duration were treated with tablets containing 0.02-0.2 g of saponins from Dioscorea caucasia. After three months blood cholesterol levels had normalised in most patients along with improvements in blood pressure, relief of dizziness and headaches and improvement of memory and working capacity.
• Various studies on animals have shown that total saponin extracts of Dioscorea nipponica and
D. caucasia have important effects on the cardiovascular system. These include a lowering of blood pressure, slowing of heart rate; improvement in ECG readings in experimentally induced myocardial ischaemia, and increased coronary blood flow. Generally IV treatments were superior to oral administration in these studies, but both oral and intravenous Dioscorea preparations were more efficacious than controls.
• A dose dependent effect on smooth muscles was found in a study examining the effect of Dioscorea nipponica on isolated rabbit uteri. At low concentrations the saponins stimulated the muscle, while at high concentration inhibition was noted. This same effect was also shown in isolated intestinal muscles, with large doses reducing the tension of most intestinal segments.
The cardiotonic effects of Dioscorea nipponica and D. caucasia are not reported for the species
commonly used in Western herbal medicine.
Clinical uses
Gastrointestinal tract
• Intestinal colic, flatulence14 and cramps1
• Diverticulitis1, cholecystitis1, bilious colic7
Reproductive tract
• Dysmenorrhoea, ovarian pain18
• Nausea in pregnancy7
• Threatened miscarriage14,18
Cardiovascular system
• Intermittent claudication1
• Hypercholesterolaemia31
• Coronary insufficiency and hypertension are reported as indications for Dioscorea nipponica and D. caucasia used in TCM15
Musculoskeletal system
• Rheumatoid arthritis (acute), rheumatism, muscular cramps1
• Pain and stiffness in lower back and knees13
Nervous System
• Autonomic nervous system relaxant, especially for gastrointestinal conditions, vegetative
neuroses and hyperaesthesia.19
Urinary Tract
• Renal colic, cystitis14
Toxicity No toxicity documented for Dioscorea spp commonly used in Western herbal medicine.
Contraindications
Similar to Dioscorea nipponica15, mild diarrhoea is sometimes reported. Dioscorea spp. should
therefore be used cautiously in those who have ‘weak digestion’ and develop diarrhoea easily.
Uses in pregnancy and lactation
Generally considered safe in all trimesters of pregnancy and is traditionally indicated for nausea of
pregnancy,12,18 and for prevention of early miscarriage14.
Interactions (drug, herb, food)None reported at normal therapeutic doses.
Dosage1
Fluid extract: 2-4 mL TDS
Dried herb by infusion or decoction 2-4 g TDS.
Useful herbal combinations
Reproductive Tract
• With Viburnum opulus, V. prunifolium, Paeonia lactiflora, Caulophyllum thalictroides and Zingiber officinalis for dysmenorrhoea.
• With Anemone pulsatilla for ovarian pain.
• With Vitex agnus castus and/or Cimicifuga racemosa; Hypericum perforatum and/or Humulus lupulus; Salvia officinalis and/or Chamaelirium luteum, for menopausal hot flushes, insomnia and mood changes.
• With Viburnum prunifolium, Paeonia lactiflora, Chamaelirium luteum, Ligusticum wallichii and Vitex agnus castus for premature labour or prevention of miscarriage.
• With Ballota nigra, Zingiber officinalis, Silybum marianum or Erythraea centaurium for nausea in pregnancy.
Gastrointestinal Tract
• Combines well with Matricaria recutita, Zingiber officinalis, Viburnum opulus for treating intestinal cramping and colic.
• With Berberis vulgaris, Cynara scolymus and Taraxacum officinale as a cholagogoue
Musculoskeletal System
• For rheumatism and arthritis combine with Cimicifuga racemosa, Guaiacum officinale, Boswellia serrata, Harpogophytum procumbens or Apium graveolens.
• For rheumatoid arthritis- acute phase – combine with Cimicifuga racemosa.5
Cardiovascular System
• For intermittent claudication and peripheral vascular disease with Salvia miltiorrhiza, Capsicumannum, Zanthoxylum americanum and Ginkgo biloba.
WILD YAM CREAMS:
Wild yam creams have become popular over recent years and various claims have been made regarding their therapeutic actions and their effect on progesterone levels. Some manufacturers claim that wild yam creams and ‘natural progesterone’ are synonymous and cite the beneficial actions of progesterone as reported by Dr John Lee as evidence of similar therapeutic gains to be had from the use of wild yam creams.
These claims are based on the belief that the diosgenin in wild yam is converted into progesterone once absorbed transdermally. This seems to be related to confusion regarding the in vitro manufacture of progesterone using Dioscorea spp and what occurs when a Dioscorea-containing cream is applied topically. In vivo hydrolysation of the saponin glycosides (dioscin, botogenin and diodenin) is unlikely when wild yam creams are applied transdermally, since this process is only known to occur in a laboratory or in the gut by the action of bacteria.
Wild yam creams do not appear to increase progesterone levels (see above), and their therapeutic
effects are cannot be attributed to diosgenin since they are largely devoid of this sapogenin. The saponin glycosides are the most likely candidates for any perceived activity, but their effects are likely to be oestrogenic. Very little, however is known of their in vivo actions and any claims can only be speculative.
Dosage instructions vary between different products, and some contain additional herbs such as Vitex agnus castus. Follow manufacturer’s instructions.
1 Scientific Committee British Herbal Medicine Association, 1983, British Herbal Pharmacopoeia. British Herbal Medicine Association, West Yorks, UK, pp 78-9.
2 Chevallier, A, 1996, The Encyclopedia of Medicinal Plants, Dorling Kindersley, London, p 89.
3 Wren, RC, 1988, Potter’s New Cyclopaedia of Botanical Drugs and Preparations, CW Daniel Company, Essex,England, p.283.
4 Wichtl, M, 1989, Herbal Drugs & Phytopharmaceuticals, Grainger Bisset, N, (ed), Medpharm Scientific Publishers, Stuttgart, Germany, p.204.
5 Hoffman, D, 1983, The Holistic Herbal, Findhorn Press, Moray, Scotland, p.229.
6 Willard, T, 1992, Textbook of Advanced Herbology, Wild Rose College of Natural Healing, Aberta, Canada, p 123.
7 Fisher, C, Painter, G, 1996, Materia Medica of Western Herbs for the Southern Hemisphere, C. Fisher/G. Painter, Aukland, New Zealand, p. 91.
8 Yen, KY, 1992, The Illustrated Chinese Materia Medica, SMC Publishing Inc., Taiwan, Republic of China, p 84.
9 Lassak, EV, McCarthy, TM, 1983, Australian Medicinal Plants, Methuen, North Ryde, NSW, p 186.
10 Lust, J., 1974, The Herb Book, Bantam, New York, p. 401.
11 Willard, T, 1991, Wild Rose Scientific Herbal, Wild Rose College of Natural Healing Ltd., Alberta, Canada, p 343.
12 Grieve, M, 1931, A Modern Herbal, Penguin, Middlesex, England, p. 91.
13 Reid, DP, 1987, Chinese Herbal Medicine, CFW Publications, Hong Kong, p.111.
14 Mabey, R, (ed), 1988, The Complete New Herbal, Gaia Books, London, p.56.
15 Chang, H, But, PP, (eds), 1987, Pharmacology and Applications of Chinese Materia Medica, World Scientific Press,Singapore, p 914.
16 Weiss, R, 1988, Herbal Medicine, Beaconsfield Publishers, England, p.330.
17 Karnick, CR, 1994 Pharmacopoeial Standards of Herbal Plants, Vol II, Sri Satguru Publications, Dehli, India, p 144.
18 McIntyre, A, 1995, The Complete Woman’s Herbal, Hodder Headline, Pty. Ltd., Australia, p 29.
19 Priest, AW, Priest, LR, 1982, Herbal Medication, LN Fowler and Co. Ltd., Essex, p. 68.
20 Bruneton, J, 1995, Pharmacology, Phytochemistry, Medicinal Plants, Lavoisier, Paris, France, p 546.
21 Sauvaire, Y, Ribes, G, Baissac, Y, et al, 1994, “Saponins extracted from vegetables fro treatment of
hypercholesterolemia, nutrition and metabolism disorders”, in Chem Abstr 24, Abst. No. 124: 298928x, 1996.
22 Sokolova, L.N., Med Prom SSSR, 7, p.43, 1961, in Chang, H, But, PP, (eds), 1987, Pharmacology and Applications
of Chinese Materia Medica, World Scientific Press, Singapore, p 914.
23 Sokolova, L.N., Farmakologiia I Toksikologiia, 22(1), p.42, 1959, in Chang, H, But, PP, (eds), 1987, Pharmacology and Applications of Chinese Materia Medica, World Scientific Press, Singapore, p 914.
24 Rao, A., Rao, A.R., Kale, R.K., “Diosgenin - A growth stimulator of mammary gland of ovariectomised mouse”, Indian J Exp Biol. 30(5): pp 367-70, 1992.
25 Syroc, VN, Kravets, KD, Khushbaktova, ZA, et al, “Steroid genins and glycosides as antiinflammatory agents”, Khim.-Farm. Zh. 26(5): pp 71-6, 1992.
26 Flaaoeyen, A, Smith, BL, Miles, CO, “An attempt to reproduce crystal-associated cholangitis in lambs by the experimental dosing of sarsasapogenin or diosgenin alone and in combination with sporidesmin”, N. Z. Vet. J., 41(4):pp 171-4, 1993.
27 Beckham, N., “Phyto-oestrogens and compounds that affect oestrogen metabolism; Part 11”, Aust J Med Herbalism, 7(2), pp.27-33, 1995.
28 Dollbaum, C, Townsend Letter for Doctors, 10, p. 104, 1996.
29 Zava, DT, Dollbaum, CM, Blen, M, “Estrogen and progestin bioactivity of foods, herbs and spices”, Proc Society for Experimental Biology and Medicine, 217(3), pp.369-78, 1998.
30 Araghiniknam, M, Chung, S, Nelson-White, T, et al, “Antioxidant activity of disocorea and dehydroepiandrosterone (DHEA) in older humans”, Life Sci, 59(11) pp 147-57, 1996.
31 Indrayanto, G, Utami, W, Santosa, MH, et al, “Diosgenin”, Anal Profiles Drug Subst. Excipients, 23: pp 99-124, 1994.