The literature is full of warnings to not ingest Comfrey, especially the root, due to the pyrrolizidine alkaloids (hereafter noted as PAs) that it contains. In the past twenty years Comfrey has been linked to four cases of veno-occlusive disease worldwide. However, these cases involved long-term, abusive doses of Comfrey tea (e.g., ten cups of Comfrey tea plus handfuls of Comfrey-pepsin tablets every day for years). “The studies already performed certify that PAs have an acute hepatotoxic effect and a carcinogenic effect with chronic application; therefore, they confirm the opinion stated in the expert textbooks that the hepatotoxicity and carcinogenicity of these PAs is considered proven. Considering this fact, the use of higher constituent levels or an exposure of longer duration are connected with damaging effects, which go beyond the responsible measure of the insights of medical science. This evaluation corresponds to current scientific knowledge, regarding a methodical procedure for identifying carcinogenic substances, and the interpretation of existing reports. The data are scientifically defendable and therefore, sufficient. The demand for further evidence concerning the establishment of risk, before a decision is made, can therefore not be considered.”
Studies done in the United States have found that, “there is extreme variability in the PA content of commercial Comfrey products. Products containing Comfrey in combination with other ingredients were found to contain the lowest alkaloid levels, while the highest levels were found in bulk Comfrey root, followed by bulk Comfrey leaf. Hot water infusions of both Comfrey leaf and root were prepared and also proved to contain PAs; this is contrary to claims by proponents of Comfrey leaf who maintain that it is harmless because its PA levels are low and because PAs are not particularly water-soluble.”
These two articles are echoed throughout the literature in one way or another. The one article that I read which opposes these was by Dr. D.B. Long, Ph.D., M.A. He adequately explains the actions of pyrrolizidine alkaloids and which ones are active in Comfrey. He then goes on to critique two of the major studies done on this topic. The first one was done by the Chemistry Department of the University of Exeter in conjunction with the Toxicology Unit of the Medical Research Council at Carshalton and the Michaelis Nutritional Research Laboratory at Harpenden, England. Their studies consisted of 1) The extraction and purification of the alkaloid for direct injection into rats to determine immediate toxicity, 2) Direct feeding experiments with rats to determine long-term chronic effects, and 3) The determination of alkaloid content in the green leaves of various Comfrey clones. To summarize Dr. Long's critique, he noted that the method used was effective in separating out closely related alkaloid compounds, but is less reliable in giving repetitively reproducible results.
The second study that Dr. Long critiqued was done by Furuya and Araki in Japan. They confined their research to Symphytum asperrimum (not the one used medicinally) and they, too, extracted the alkaloids from the plant and fed it to rats. They gave the rats an intravenous injection of 300 mg of the purified alkaloid per Kg of rat tissue and this caused death in approximately 50 percent of the experimental animals. In reference to this Dr. Long notes, “Thus in the case of Comfrey tea if it be assumed that normal methods of infusion could extract just over half the alkaloid that was extracted by 8 hours in a Soxhlet apparatus in the laboratory, each cup of tea could contain 100 micrograms of alkaloid. At this level the consumer could never attain the lethal dose of 300 milligrams/Kg tissue found necessary to produce the acute reaction in rats. Even to consume this quantity it would take a 150 lb. man drinking 4 cups of tea per day a total of 140 years. Furthermore it is known that to produce chronic reactions, sub-lethal doses over a prolonged period are necessary.”
Dr. Long concludes his analysis of the studies by saying that the use of Comfrey as food for mankind or animals does not present a toxic hazard from alkaloids. He notes that extensive use of the herb as forage for animals has failed to reveal any deleterious effects, but instead has had considerable benefits to them. He states again that the alkaloid content is lower when the herb is used in its wholesome state.
There are some interesting things that I noticed as I researched this herb, of which I will now note. First, there is no definition for pyrrolizidine in the Merck Index (twelfth edition, 1996), nor in the dictionary, nor in my medical dictionaries-the word does not exist in these books. The source in which I found some information was online. Still, none of the literature that I found would make a list of the PAs that are in Comfrey. Even Dr. Duke's database doesn't tell you exactly which ones are the noted pyrrolizidine alkaloids. In studying the chemical constituents list noted in Dr. Duke's database, I could not help but notice a few important chemical activities that are never mentioned in any of the literature that I have read to date.
For example, the following chemical constituents are listed as anti-hepatotoxic, hepatoprotective or otherwise liver-building: ascorbic-acid, found in the root at 132 ppm; beta-carotene, found in the root at 660 ppm; caffeic-acid, found in the root in trace amounts; carotenes, found in the whole plant at 6,300 ppm and one carotene is turned into two beta-carotenes in the body, putting the liver-building potential (when combined with beta-carotene) at 13,260 ppm. Comfrey is the plant that contains the highest amount of carotenes on Dr. Duke's list. To give you a contrast, the carrot, known as a tremendous liver builder, has 673 ppm of beta-carotene in its root. Then additionally Comfrey contains chlorogenic-acid, found in the root in trace amounts; choline, found in the root in trace amounts; glucose, found in the root in trace amounts; glucuronic-acid, found in the root in trace amounts; iron, found in the root at 810 ppm; niacin, found in the root in trace amounts; rosmarinic-acid, found in the leaf at 5,000ppm; selenium, found in the root in trace amounts; stigmasterol, found in the root in trace amounts; tannin, found in the plant at 80,000-90,000 ppm.
Some simple arithmetic puts the liver-building, hepatoprotective chemicals in the root at 1,602 ppm plus the eight constituents listed that are found in trace amounts. The amounts found in the plant and leaf come to a total of 101,300 ppm!
Now, let's compare that to the pyrrolizidine alkaloids, the chemicals noted on Dr. Duke's list as toxic or hepatotoxic: consolicine, found in the root in trace amounts; consolidine, found in the root at 17 ppm; echimidine, found in the root in trace amounts; heliosupine-n-oxide, found in the root in trace amounts; lasiocarpine, found in the root in trace amounts; lycopsamine, found in the root in trace amounts; symphytine, found in the root in trace amounts. For all of these chemicals, Symphytum is the number one (or two) plant known to contain the highest amount of this chemical. Nonetheless, if we do our math, we find that the total of PAs is 17 ppm plus the six constituents that are found in trace amounts. We have 102,902 ppm of liver-building, anti-hepatotoxic constituents as compared to 17 ppm of hepatotoxic constituents-not counting the trace amounts found on both sides. Although I am not a chemist, this discrepancy is glaring and needs investigation. My intent is to research this discrepancy.
I also find it interesting that four deaths in twenty years has given the FDA reason to blacklist Comfrey, and yet thousands of people die (or suffer serious and life-threatening side effects) each year from prescription drugs, chemotherapy, misdiagnoses and many other forms of modern medicine. Have we lost the good of reason here? Or do we have a political struggle that is rooted in greed and the lust for power?
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