Public Health Nutrition

Research Article

Analysis of herbal teas made from the leaves of comfrey (Symphytum officinale): reduction of N-oxides results in order of magnitude increases in the measurable concentration of pyrrolizidine alkaloids

Nicholas H Oberliesa1 c1, Nam-Cheol Kima1a2, Dolores R Brinea3, Bradley J Collinsa4, Robert W Handya3, Charles M Sparacinoa3, Mansukh C Wania1 and Monroe E Walla1

a1 Natural Products Laboratory, RTI International, PO Box 12194, Research Triangle Park, NC 27709, USA

a2 Lovelace Respiratory Research Institute, Albuquerque, NM, USA

a3 Health Sciences Unit, RTI International, Research Triangle Park, NC, USA

a4 National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA


Objectives: To determine the relative quantities of two hepatotoxic pyrrolizidine alkaloids, symphytine and echimidine, in teas prepared from comfrey leaves (Symphytum officinale), and to determine the potential contribution of the N-oxide forms of these alkaloids to levels of the parent alkaloids.

Design: Comfrey leaves were purchased from three commercial sources and used to prepare tea in a manner consistent with the methods used by consumers. An extraction scheme was devised for extraction of the alkaloids, and a gas chromatographic method was developed to quantify the two major alkaloids, symphytine and echimidine. Recognising that the N-oxide derivatives of these alkaloids have also been identified in comfrey preparations, chemical reduction was applied to determine the total quantities of the alkaloids as free bases and as N-oxide derivatives.

Results: The concentration of symphytine and echimidine varied considerably between teas prepared from leaves purchased from the different vendors of plant material. Moreover, a much higher concentration of symphytine was found in the tea when steps were included to reduce N-oxides prior to analysis. The treatment of pure symphytine with hot water did not generate the N-oxide derivative de novo.

Conclusions: Since the pyrrolizidine alkaloids are known to be hepatotoxic, consumption of herbal teas made from comfrey leaves may be ill-advised. The concentration of pyrrolizidine alkaloids in such teas may be underestimated substantially unless the concentration of N-oxides is taken into consideration.

(Received January 04 2004)

(Accepted March 23 2004)


c1 *Corresponding author: Email