Rhubarb, a plant that thrives in colder climates, is predominantly found in mountainous and temperate regions such as Northeast Asia. The species Rheum x hybridum is widely cultivated as an edible vegetable across various parts of Europe and North America. Interestingly, while rhubarb is botanically categorized as a vegetable, it is often regarded as a fruit in countries like the United States. The plant features long, fibrous stalks that can vary in color from deep red to light green, and these stalks are typically chopped and sweetened with sugar due to their notably tart flavor. In contrast, its large, dark green leaves resemble spinach but are generally avoided in culinary uses, as there are concerns regarding their potential toxicity.

This article aims to deliver comprehensive insights into the safety aspects of rhubarb leaves.

High in Oxalic Acid

Rhubarb leaves are deemed inedible primarily due to their elevated levels of oxalic acid. While both the stalks and leaves contain this compound, the leaves exhibit a significantly higher concentration. Oxalic acid is a naturally occurring substance present in various plants, including leafy greens, fruits, vegetables, nuts, seeds, and cocoa. In rhubarb, the oxalate content ranges from approximately 570 to 1,900 mg per 100 grams (3.5 ounces). Notably, the leaves are the richest source, with oxalate comprising about 0.5 to 1.0% of their total weight.

Excessive intake of oxalate may result in a condition known as hyperoxaluria, characterized by the excessive excretion of oxalate in urine. This condition can lead to the accumulation of calcium oxalate crystals within the organs. In the kidneys, such accumulation can precipitate the development of kidney stones, potentially culminating in kidney failure.

Symptoms associated with mild poisoning from rhubarb leaves include vomiting and diarrhea, which typically resolve within a few hours. However, more severe toxicity from oxalates can manifest as a sore throat, difficulty swallowing, nausea, vomiting (sometimes with blood), diarrhea, and abdominal pain. In extreme cases, symptoms may escalate to include kidney failure, numbness, muscle twitches, and cramps.

In summary, rhubarb leaves contain oxalic acid, which poses a risk of organ buildup and can lead to serious conditions such as kidney stones and kidney failure if consumed in substantial amounts.

Rhubarb Leaf Poisoning: A Rare Occurrence

Incidents of poisoning resulting from the consumption of rhubarb leaves are exceedingly rare. The average lethal dose of oxalate is estimated to be around 170 mg per pound (approximately 375 mg per kg) of body weight, translating to about 26.3 grams for an individual weighing 154 pounds (70 kg). This indicates that one would need to consume between 5.7 and 11.7 pounds (2.6 to 5.3 kg) of rhubarb leaves to reach a potentially lethal dose of oxalate, contingent on the oxalate concentration present in the leaves.

Interestingly, there have been reports of lethal outcomes arising from lower consumption levels. During World War I, individuals were encouraged to use rhubarb leaves as a substitute for vegetables that were scarce, which unfortunately led to several cases of poisoning and fatalities. There were also occurrences of poisonings reported in the 1960s. However, due to the infrequent consumption of rhubarb leaves in modern diets, there have been no documented deaths in recent years linked to their ingestion.

Nonetheless, it is important to note that there have been instances of individuals experiencing kidney damage from consuming large quantities of rhubarb stems, which also contain oxalic acid. Certain individuals may be at a heightened risk of developing kidney stones and damage due to oxalates, including those with specific genetic predispositions, pre-existing kidney damage, excessive vitamin C intake, or a deficiency in vitamin B6.

Interestingly, it has been proposed that both fatal and nonfatal poisoning cases associated with rhubarb leaves could possibly be attributed to another compound known as anthraquinone glycosides, rather than solely the oxalic acid. However, further research is necessary to clarify this hypothesis.

In conclusion, reports of poisoning due to rhubarb leaves are exceptionally scarce. A significant intake of rhubarb leaves would generally be required to elicit symptoms, although certain individuals may be more vulnerable to kidney issues stemming from oxalate consumption.

The Bottom Line

Rhubarb leaves possess significant quantities of oxalic acid, which can lead to various health issues if consumed in excessive amounts. This can result in symptoms ranging from mild gastrointestinal discomfort to more severe complications, including the formation of kidney stones and potential kidney failure.

While instances of poisoning are infrequent, it is advisable to steer clear of consuming rhubarb leaves, especially for individuals with preexisting conditions that heighten their vulnerability to kidney stones.