Holly berries are deadly . . . right?

If you frequent trendy coffee houses you may be familiar with yerba mate, a caffeinated beverage 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 is holly 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 holly (Ilex opaca) and European holly (Ilex aquiflorium), the bright-red-berry-bearing varieties used for holiday decorating, aren’t members of that select group and 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, neither of the others does.

Saponins take the blame

Saponins at work.
Saponins at work.

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 and 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, root beer 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, and as the leaves grow thicker, spinier and less appealing, saponin levels drop. But while it’s best for a holly bush to have its leaves left intact, it also needs to have its seeds dispersed. Saponin levels fall in holly berries as they mature and are lowest in winter, when the berries become a critical food source for birds and other small creatures.

Birds eat holly. 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, resulting in pain and injury from the sharp spines.

As for the berries: Despite all the scary warnings about their deadly nature, actual evidence of toxicity is hard to find. Extremely large ingestions may or may not cause GI distress; one study that looked at ingestions by children found that only the ones given ipecac or another emetic vomited or had any symptoms at all.

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

  • Holly leaves and berries are most toxic when they are immature, and are least toxic in the winter.
  • The leaves are lined with sharp spines that can cause injury.
  • The saponins in the berries is thought to 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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