{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,3]],"date-time":"2026-10-03T12:39:49Z","timestamp":1791031189019,"version":"4.1.0"},"reference-count":41,"publisher":"Cambridge University Press (CUP)","issue":"7","license":[{"start":{"date-parts":[[2007,1,2]],"date-time":"2007-01-02T00:00:00Z","timestamp":1167696000000},"content-version":"unspecified","delay-in-days":823,"URL":"https:\/\/www.cambridge.org\/core\/terms"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Public Health Nutr."],"published-print":{"date-parts":[[2004,10]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:sec id=\"S1368980004001156_sec01\"><jats:title>Objectives:<\/jats:title><jats:p>To determine the relative quantities of two hepatotoxic pyrrolizidine alkaloids, symphytine and echimidine, in teas prepared from comfrey leaves (<jats:italic>Symphytum officinale<\/jats:italic>), and to determine the potential contribution of the<jats:italic>N<\/jats:italic>-oxide forms of these alkaloids to levels of the parent alkaloids.<\/jats:p><\/jats:sec><jats:sec id=\"S1368980004001156_sec02\"><jats:title>Design:<\/jats:title><jats:p>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<jats:italic>N<\/jats:italic>-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<jats:italic>N<\/jats:italic>-oxide derivatives.<\/jats:p><\/jats:sec><jats:sec id=\"S1368980004001156_sec03\"><jats:title>Results:<\/jats:title><jats:p>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<jats:italic>N<\/jats:italic>-oxides prior to analysis. The treatment of pure symphytine with hot water did not generate the<jats:italic>N<\/jats:italic>-oxide derivative<jats:italic>de novo<\/jats:italic>.<\/jats:p><\/jats:sec><jats:sec id=\"S1368980004001156_sec04\"><jats:title>Conclusions:<\/jats:title><jats:p>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<jats:italic>N<\/jats:italic>-oxides is taken into consideration.<\/jats:p><\/jats:sec>","DOI":"10.1079\/phn2004624","type":"journal-article","created":{"date-parts":[[2004,10,13]],"date-time":"2004-10-13T22:28:46Z","timestamp":1097706526000},"page":"919-924","source":"Crossref","is-referenced-by-count":41,"title":["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"],"prefix":"10.1017","volume":"7","author":[{"given":"Nicholas H","family":"Oberlies","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nam-Cheol","family":"Kim","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dolores 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