Are holly berries poisonous?
If you frequent trendy coffee houses you may be familiar with yerba mate. This popular caffeinated beverage is made from holly’s South American cousin Ilex paraguariensisa. As we all know, just because one member of a family is stimulating, that doesn’t mean another can’t be toxic. But are holly berries poisonous?
Research into holly’s chemical components has been surprisingly limited, and studies of potential toxicity even more so. The relatively little work that has been done has been concentrated primarily on Ilex varieties that, like yerba mate, have long histories of being used for tea, food or traditional medicines.
American (Ilex opaca) and European (Ilex aquiflorium) hollies, the varieties used for holiday decorating, aren’t members of that select group. What we think we know about them tends to come from hoary anecdotes of uncertain provenance. The allegations of toxicity are many, but the evidence is thin.
Not that there hasn’t been any study at all. In 1919, as part of the war effort, the USDA investigated native Ilex varieties as potential homegrown sources of caffeine. They found that although the native yaupon (the misnamed Ilex vomitoria, mistakenly thought to have been used as an emetic by native Americans) contains plenty of caffeine, the others do not.
Saponins take the blame
What the hollies do contain, both in their berries and their leaves, are saponins. Saponins are sugar-containing compounds that foam up when agitated in water. They are commonly found in a number of plants including oats, spinach, peas and soybeans. In fact, it’s plant-derived saponins that make your beer, soda pop and shampoo nice and foamy.
The saponins in holly contain glucose but they taste bitter rather than sweet, helping deter grazing herbivores. In addition to their bad taste they are reputed to cause nausea, vomiting and diarrhea.
Saponin levels are highest in holly leaves when they are young and tender. As the leaves grow thicker, spinier and less appealing, saponin levels drop. But while a holly bush wants to keep its leaves intact, it also needs its seeds dispersed. Saponin levels also fall in holly berries as they mature; they are lowest in winter, when the berries become a critical food source for birds and other small creatures.
Birds eat holly berries. Why can’t we?
The lack of study makes this question hard to answer. Holly leaves are hard to eat because they’re thick, waxy and have sharp, thorn-like spines along their edges. Children are unlikely to give them a go, but of course a dog might try, suffering injury from the sharp spines.
As for holly berries: Despite all the scary warnings about their deadly nature, evidence of toxicity is hard to find. Extremely large ingestions may or may not cause GI distress; one study found only children given ipecac or another emetic after eating holly berries had any symptoms at all. In other words, they were made sick by the treatment, rather than the berries.
Ilex saponins can damage red blood cells if they come in direct contact, but this doesn’t happen when holly is ingested. Instead, the saponins are largely rendered inactive by being bound up with cholesterol. In fact, research is underway to determine if saponins can be used as cholesterol-lowering medications.
The bottom line on holly berries
- Holly leaves and berries are most toxic when they are immature, and are least toxic in winter.
- The leaves are lined with sharp spines that can cause injury.
- The saponins in the berries may cause GI upset when ingested in large quantities, but there is scant evidence of this.
If a child or pet has eaten holly berries, follow the usual advice for accidental ingestions: Wipe any berries from the mouth and give water to drink. Call your vet if your pet has eaten leaves and shows signs of having mouth or throat pain. And as always, call poison control (800-222-1222) for further questions and advice.
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