A perennial that grows to about 3 feet. It has lanceolate leaves and bell-shaped purple or yellow-white flowers. It grows in moist grasslands.
Comfrey has been cultivated in Japan as a green vegetable and has been used in American herbal medicine.1 Its old name, knitbone, derives from the exter?nal use of poultices of the leaves and roots to heal burns, sprains, swelling and bruises. Comfrey has been claimed to heal gastric ulcers, hemorrhoids and to suppress bronchial congestion and inflammation.1 Its use has spanned over 2000 years.
The healing action of the poultices of the roots and leaves may be related to the presence of allantoin, an agent which promotes cell proliferation. The underground parts contain 0.6%-0.7% allantoin and 4%?6.5% tannin. The leaves are poorer in allantoin, but richer in tannin. It has been recently found that the roots contain about 100 times the alkaloid content as compared to the aerial portions. Large amounts of mucilage are found in both leaves and roots.3 Rosmarinic acid,5 lith os?permic acid5 and a pentacyclic triterpene glycoside of oleonolic acid6 have been identified in the root. The alkaloid content of S. asperum ranges from 0.14% to 0.4%.7 Numerous pyrrolizidine alkaloids have also been isolated from comfrey.
Ointments containing comfrey have been found to possess an anti-inflammatory activity, which appears to be related to the presence of allantoin and rosmarinic acid or to another hydrocolloid poly?saccharide.9 Lithospermic acid, isolated from the root, appears to have anti gonadotropic activity.
Despite its common use, the long-term ingestion of comfrey may pose a health hazard. Several members of the family Boraginaceae ( Senecio, Heliotro?pium) contain related alkaloids reported to cause liver toxicity in animals and humans. Some of these com?pounds predispose hepatic tumor development.
The carcinogenic potential of S. officinale was tested in rats fed 0.5% to 8% comfrey root or leaves for 600 days. Signs of liver toxicity were seen within 180 days and hepatocellular adenomas were induced in all grou~Urinary bladder tumors were also induced at the lowel comfrey levels. The incidence of liver tumors was hig~in groups fed a diet of roots rather than leaves.
The pyrrolizidine alkaloids symphytine, echimidine11 arlasiocarpine have been found in S. officina/e. Of thes lasiocarpine 12 and symphytine have been shown to I' carcinogenic in rats.13 In a recent experiment, rats weu given doses of 50 mg/kg of comfrey-derived Subsequent liver analysis showed vascular necrosis and hepatocyte cellular membrane damage.! This liver damage was evident and was dose depedent.
Similarly, the alkaloids of Russian comfrey cause, chronic liver damage and pancreatic islet cell tumorsafte.
2 years of use in animal models. Eight alkaloids been isolated from Symphytum + uplandicum.16 Alkaloi levels range from 0.003% to 0.115% with highest concej trations in small young leaves. Of the 7200 inhabitan~ observed, 23% had severe liver impairment. An indire( estimate of alkaloid ingestion determined the consumf tion of toxic alkaloids to be 2 mg/700 g of flour. Basedo..
this value, Roitman's calculation of 8 to 26 mg of toxi alkaloids per cup of comfrey root tea (4 to 13 times great as the episode above) suggests that comfrey ingestion poses a significant health risk. Herbal teas anI similar preparations of Symphytum contain the pyrrolizi dine alkaloid which has shown to cause blockage hepatic veins and lead to hepatonecrosis.
Venoocclu. sive disease has been reported in a woman who ingeste a comfrey-pepsin preparation for 4 months; 18 one woma died following the ingestion of large quantities of yerb mate tea (/lex paraguariensis) which also contains P?rolizidine alkaloids. A woman who consumed amounts of comfrey preparations developed ascites, caused veno-occlusive disease and four Chinese women who self-medicated with an herbal preparation that contained pyrrolizidine alkaloids from an unknow
plant source also developed the disease. One man presented portal hypertension with hepatic veno-occlu. sive disease and later died of liver failure. It was discov. ered that he used comfrey in his vegetarian diet.
Oral ingestion of pyrrolizidine-containing plants such as com. frey poses the greatest risk since the alkaloids ale converted to toxic pyrrole-like derivatives following ingestion.