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The publication of the rodent toxicity studies in the 1970's and 1980's led to the obvious question of comfrey safety in humans. Since comfrey leaf was a commonly available tea in both the United States and the United Kingdom and many people had been consuming it for years, there was a readily available exposed population. Anderson et al set out to determine if occult liver damage was apparent in twenty-nine healthy people that had been taking comfrey on a long term basis. Individuals in the study had been using 0.5 to 25 grams of comfrey leaf per day for 1 to 30 years. Although, liver damage can only be definitively determined by visual inspection of tissue obtained from a biopsy, serum markers for liver pathology are a good indication of liver disease. The researchers measured aspartate aminotransferase (AST), gamma-glutamyltransferase (AST), bilirubin, and alpha-fetoptotein (AFP) as markers of liver inflammation, choleostasis, and cancer. All measurements in this small uncontrolled study were within normal ranges.
The presence of PAs in comfrey does present a health risk to humans that ingest it. However, the extent of this risk has not been determined and there is a great deal of evidence suggesting safe use in humans is possible. In order to determine risk, the characteristics of the plant material used (root or leaf, young or old) and the health status of the individual human need to be considered. The risk of liver damage to any one individual is dependent on that person's nutritional status, their current use of hepatotoxic drugs as well as intake of food/drugs that effect liver metabolism. Veno-occlusive disease (VOD) manifesting in people using comfrey has been reported (see Case Reports). In all instances, a clear cause and effect correlation is not present. Other factors that may have amplified the risk of liver damage are present.
© 2004 Dorena Rode       Acknowledgment