Caution needed when eating wild asparagus
The wild asparagus season is here. Although considered to be edible, this plant can cause potentially serious poisoning: swelling of the throat, difficulty swallowing, etc. These symptoms generally occur three to four hours after consumption. Laboratory analysis of wild asparagus samples has revealed the presence of numerous calcium oxalate raphides, microscopic crystals known for their irritating effect.
Wild asparagus is a wild, almond-green plant belonging to the Asparagaceae family. Its spiky flower buds are eaten with vinaigrette or as an accompaniment to a meal. It is a seasonal plant, growing between April and June in meadows, embankments and woods throughout most of mainland France and Corsica. It can also be grown by individuals in their vegetable gardens from commercially available seeds. This plant has been sold at markets and in some supermarkets for a number of years now.
Symptoms within hours of eating wild asparagus
Over the last few years, poison control centres (PCCs) have been receiving calls from people experiencing symptoms after eating wild asparagus. In May 2019, the Nancy PCC had alerted ANSES following a case of serious poisoning with life-threatening symptoms. Between January 2010 and June 2020, the PCCs recorded 48 cases of poisoning due to the consumption of wild asparagus.
Symptoms mainly included intense pharyngeal pain, swelling in the mouth or throat and difficulty swallowing. What was notable about these symptoms was that they occurred on average three hours after consumption, rather than immediately, as usually happens with an allergic reaction or immediate irritation. Moreover, during the same meal, some consumers were affected while others were not, suggesting individual susceptibility. The toxicity of this asparagus is not eliminated by cooking.
What should be done if symptoms develop after eating wild asparagus?
- Call 15 or 112 (or 114 for the hearing impaired) in the event of a life-threatening condition and mention the consumption of wild asparagus.
- Call a poison control centre or see a doctor.
- Take photographs of the plants before cooking as this can help identify them in the event of poisoning.
- Keep any meal leftovers so that they can be analysed for toxic substances.
Large quantities of calcium oxalate crystals
To identify the causes of this poisoning, ANSES funded a study that was carried out between 2022 and 2023 by the Nancy PCC and the pharmacognosy laboratory at the Paris Faculty of Pharmacy.
It involved gathering detailed information on poisoning cases due to wild asparagus, and developing methods for analysing the plant in order to identify its constituent substances. Samples of wild asparagus were collected from poisoning victims or purchased from markets.
Analysis of the plant revealed abundant calcium oxalate raphides. These microscopic crystals in the form of fine needles are found in many other plant families, including Araceae (arum, dieffenbachia, etc.), that are known to irritate the skin and mucous membranes upon contact.
The most likely hypothesis is that these crystals damage the skin and mucous membranes and facilitate the entry of inflammatory or toxic substances, causing local swelling of the tissues. The mucilage also identified in asparagus might initially play a protective role, acting as a gel that traps the raphides, then gradually releasing them during digestion, thus explaining the delayed onset of symptoms after ingestion.
Further research is needed to quantify the raphide crystals in wild asparagus and to precisely identify the substances responsible for the inflammation.