New Information on Elderberry Toxicity
by Rebekah Bailey
Conventional
wisdom regarding elderberries has been they are toxic when raw, and that the
cyanide producing compound in them is neutralized with heat. Elderberry
branches, stems, leaves, and seeds contain potential cyanide in the form
of cyanogenic glycosides. When ingested, these glycosides react with an
enzyme, beta-glucosidase, and hydrolyze, releasing hydrogen cyanide.
Elderberries aren't the only food containing cyanogenic glycosides: Lima beans,
flax seed, almonds, apple seeds, cherry and plum pits, apricot and peach pits,
cassava (the source of tapioca), spinach, peas, soy, and bamboo shoots. However, I don't see anyone losing sleep
over eating spinach and lima beans ... ummm, well, maybe if you don't like
those vegetables.
Exposure to small amounts of cyanide can cause dizziness, headache, nausea, vomiting, rapid breathing, and rapid heart rate. Exposure to larger amounts can cause convulsions, loss of consciousness, low blood pressure, and respiratory failure. How much ingested cyanide is toxic to human beings? Well I couldn't find an exact number, but one source cited 98 mg in one day (and stated the lowest documented lethal dose as 37.8 mg), and the John Hopkins Center for Health Security cites 100-200 mg when ingested as sodium or potassium cyanide. Another source cited "0.5-3.5 mg/kg bw. Approximately 50-60 mg of free cyanide constitutes a lethal dose for an adult man." The human body is able to clear small amounts of cyanide through the liver involving a molecule called thiosulfate, and if enough tiosulfate is not present, then cyanide poisoning occurs. Taking this into account, it stands to reason that poisoning will vary from person to person, depending on body weight, fasting/non-fasting, and individual metabolic factors.
Having a general idea of how much cyanide is lethal, the next question is how much cyanide can you find in elderberry? I could only find a couple of sources, which both stated 3mg per 100 g of fresh berries, and up to 17mg per 100 g of fresh leaves. However, when I followed up with both articles' source material, Assessment Report on Sambucus nigra L., fructus by the European Medicines Agency, I could find no such numbers. What the report did state was that information regarding the level of cyanogenic glycosides in the fruits and seed was not available. Of the two sources I found, one came to the conclusion that it’s inconclusive just what the concentration of cyanogenic glycosides found in the berries and flowers. If you were to go by the amount of 3 mg, then it would take eating approximately 3 pounds of raw elderberries to get a toxic dose of cyanide.
Here is where the new Missouri University elderberry study becomes relevant. The University, working in conjunction with several state agencies and farmers, have been exploring elderberry as a commercial crop. A range of different studies have been conducted and written about, the most recent focusing on the toxicity issue.
The study focused on American Elderberry (Sambucus Canadensis), which is a different species than the European Elderberry (Sambucus nigra). Thomas referenced another study which established that cyanogenic glycosides in American Elderberry are lower than those found in the European Elderberry. The toxicity study only encompassed the edible berries, and did not include the leaves, stems, and branches. Tested were ripe berries, red/under-ripe berries, green berries, and pedicels (tiny stems that attach berries to the umbel). Thomas stated that they even had a student who painstakingly separated skin, seeds, pulp, and juice of berries, so the individual parts could be tested for glycosides. Using the levels of cyanogenic glycosides found in commercial apple juice as a benchmark, the study found that all parts of the raw elderberry – green, red or ripe – contained lower levels of glycosides than commercial apple juice. The study also examined the levels of beta-glucosidase found in elderberries. Cyanogenic glycosides in elderberries represent a potential for cyanide, but only convert to cyanide if reacted with beta-glucosidase. The study found there were insufficient quantities of beta-glucosidase to convert the glucosides to cyanide.
The study
concluded that the raw berries of the American Elderberry were as safe, if not
safer, than commercial apple juice because 1) cyanogenic glycoside levels were
extremely low, and 2) insufficient quantities of beta-glucosidase were present
to convert any glycosides to cyanide.
The good news is that it doesn't matter if we know the exact levels of glycosides in elderberry. What matters is that we know that cyanide evaporates at a temperature of a little over 78°F (26°C).
I found a pretty comprehensive study of the effects of heating on cyanogenic glycosides, which was informative, and reassuring. In the study, bitter apricot seed was boiled in water for 15 minutes, resulting in a 98% reduction in glycosides. Bamboo shoots were down 91% after 15 minutes of boiling, and no detectable traces were found after 60 minutes of boiling. Cassava boiled for 20 minutes was down by 97%, and only trace glycosides were found after 35 minutes. Flax seed was dry heated for 15 minutes, resulting in only a 10% reduction in glycosides. The study referenced previous studies of dry heating which resulted in only 16-18% reductions, and concluded that dry-heating did not reduce cyanide content effectively.
I’d like to add one little side note, not related to toxicity, but relevant to heating elderberries. There are a few studies which have examined the effects of heating elderberry. One such study found “short-time heat treatment reduces potential allergy-related risks deriving from elderberry consumption without seriously affecting its properties as an antioxidant and free-radical scavenging food.” Another study indicates gentle heating may render the polyphenols in elderberry more bioavailable, but this particular aspect is still controversial, and needs additional study.
Taking all of this information into consideration, my personal conclusion is that elderberries are as safe to consume as apples, with or without heating. Care should be taken to remove leaves, stems and branches, and a short 15 minute gentle simmer shouldn’t adversely affect the beneficial properties of the berries. While not the tastiest raw berries I’ve sampled, when checking my bushes this afternoon, I didn’t hesitate to pop a handful of elderberries into my mouth.
