Summary

Buckwheat is a fast-growing annual plant usually found in the temperate zones. It is a dicotyledonous, broadleaved plant belonging to the family Polygonaceae. Buckwheat seeds comprise of protein, carbohydrates, fat, fiber, and ash. The seeds also contain flavonoids and tannins (0.5% to 4.5%). Buckwheat pollen grains are of two types: large pollen grains and small pollen grains.

Buckwheat allergy has commonly been reported in Asia. However, a significant proportion of the population is sensitized to buckwheat worldwide, including Italy (3.6%), European countries (1.0–9.7%), and the United States (US) (2.5%). Consumption of common buckwheat as noodles, dumplings or porridges instead of staple foods can attribute towards high frequency of buckwheat allergy in Asian countries. In Western countries, common buckwheat is frequently mixed with specific dishes. Pillows made with common buckwheat husks also cause allergic reactions. Several patients using pillows filled with common buckwheat husks in Germany and the US reported allergic symptoms. The main route of exposure is ingestion while inhalation is the secondary route of exposure.

Urticaria, asthma, atopic dermatitis, and allergic rhinitis are the symptoms exhibited in buckwheat allergy. Severe symptoms, including anaphylaxis may occur after ingestion or inhalation of buckwheat. Treatment of food allergy is based on avoiding causative food items after an accurate diagnosis has been established. Patients suspected of buckwheat allergy should be advised to check for common buckwheat as an ingredient while buying gluten-free food.

Buckwheat allergens are thermostable and are therefore not destroyed even after being cooked. The BW24KD is one of the major allergens in common buckwheat. Buckwheat exhibits cross-reactivity with rice, poppy seeds, hazelnut, walnut, coconut, latex, cashew nut, and quinoa.

Epidemiology

Worldwide distribution

Buckwheat allergy has commonly been reported in Asia. In Japan, it is the sixth most common cause of food allergy, with an estimated prevalence of 0.22% in Japanese school children. In Korea, the estimated prevalence of buckwheat allergy in school children is 0.10%.

Data collected from recent studies reveal that a significant proportion of the population is sensitized to buckwheat worldwide, such as in Italy (3.6%), other European countries (1.0–9.7%), and the United States (US) (2.5%). However, the exact prevalence of buckwheat allergy among sensitized individuals is unspecified. In Europe, buckwheat is considered as a hidden allergen. However, only limited data is available on the prevalence of buckwheat hypersensitivity in non-Asian countries.

Buckwheat is an emerging allergen in Italy; it is more frequently associated with sensitization in the Northern regions. In a study of 1,954 patients (61.3% of the study subjects being allergic) from Italy, it was observed that the mean prevalence of buckwheat sensitization was 3.6%, with a significant difference between Northern (4.5%), Central (2.2%), and Southern (2.8%) regions.

Buckwheat allergy is an IgE‐mediated, immediate‐type reaction, sometimes resulting in severe responses similar to those caused by soybean and peanut allergy. The allergic reaction can occur due to the ingestion of buckwheat, occupational exposure, or domestic exposure while sleeping on a pillow stuffed with buckwheat husk.

Incidences of work-related buckwheat asthma have been reported from noodle shops in Japan, Korea, Spain, France, and a health food shop in Switzerland. In Sweden asthma, rhinitis, and skin eruptions were seen in 13 out of 28 workers when handling buckwheat while repackaging health food, and 28% were sensitized to buckwheat. In a study from China, only one out of 61 individuals (2%) with either work-related exposure or frequent consumption of buckwheat had a positive skin prick test (SPT) response to buckwheat.

Risk factors

Consumption of common buckwheat as noodles, dumplings or porridges instead of staple foods can be attributable to the high frequency of buckwheat allergy in Asian countries. Japanese people consume buckwheat as 'soba' noodles. In Western countries, common buckwheat is frequently mixed with specific dishes; as an ingredient with pepper, or, present as a hidden food allergen in wheat burger, porridge, pasta and pizzas Pillows made with common buckwheat husks also cause allergic reactions. Several patients using pillows filled with common buckwheat husks in Germany and the US reported allergic symptoms. A study noted that the airborne dust recorded at the time of buckwheat flour packaging was about 1–2 mg/. It indicated that exposure to comparatively low buckwheat dust levels might induce a definite risk of developing allergy rapidly.

Route Of Exposure

Main

The main route of exposure is ingestion. Ingestion of even a small amount of common buckwheat flour or common buckwheat-containing eatables may result in severe and critical allergic symptoms.

Secondary

Another way of exposure to buckwheat allergen is inhalation. Inhalation of common buckwheat, even in small amounts, can cause allergic reactions.

Moreover, in several Asian countries, allergic reactions are caused by using pillows filled with common buckwheat husks.

Clinical Relevance

Allergic rhinitis

In the baking or noodle-manufacturing industry, buckwheat exposure might lead to an occupational health risk because of the inhalation of buckwheat dust from grinding and packaging. Buckwheat is known to trigger work-related rhinitis in bakers. Fritz et al. (2003) reported a case of a patient who had been using a buckwheat pillow and, as a result, developed asthma and a worsened situation of allergic rhinitis (AR). The SPT was 4+ to buckwheat. The patient’s symptoms were resolved after he stopped using the buckwheat pillow, indicating that his asthma and AR symptoms were buckwheat induced.

Asthma

Buckwheat exposure can prompt work-related health risks in the baking and noodle-manufacturing industry. The inhalation of buckwheat dust from binding and packaging causes respiratory symptoms, such as work-related asthma. A small amount of buckwheat flour (BF) attached to a buckwheat chaff-stuffed pillow (BCP) can induce BF sensitization. Lee et al. (2001) described a case of three children exhibiting BF allergy consequent to using a buckwheat chaff-stuffed pillow (BCP). These children underwent treatment as non-allergic asthmatics after the routine allergy skin tests and serologic tests. The researchers concluded that BCP should be considered the leading cause of nocturnal childhood asthma in asthmatic children using buckwheat-stuffed pillows.

Atopic Dermatitis

Atopic dermatitis (AD) may occur after the consumption of buckwheat. A 64-year-old African American man with no history of allergies developed an allergy to buckwheat, which is manifested as atopic dermatitis (AD). The patient presented with pruritic rashes on his arms, wrists, legs and back after consuming buckwheat cream daily for breakfast for five weeks. He was advised to stop the consumption of buckwheat and the rash subsided subsequently. The findings and clinical history indicated buckwheat as a possible cause of AD in the patient. A 47-year-old female visited a hospital after experiencing two episodes of acute urticaria. She had a medical history of grass pollen-related allergic rhino-conjunctivitis. She experienced swelling on the lips, itching of the skin, and scalp with general illness and discomfort after consuming noodles in a Japanese restaurant. Moreover, she developed itching of the skin, facial angioedema, and generalized urticaria after ingesting white and black Russian bread. She had consumed soba noodles containing buckwheat as an ingredient, and the Russian bread was prepared from buckwheat flour. The patient's IgE recognized buckwheat allergens in buckwheat flour, black bread (prepared using buckwheat flour), cooked soba, and raw soba extracts. Avoidance of buckwheat improved the patient’s symptoms, and she gradually became asymptomatic.

Other diseases

Severe symptoms, including anaphylaxis, can occur after ingestion or inhalation of buckwheat. Multiple cases of buckwheat anaphylaxis have been described in the literature associated with sensitization from buckwheat pillows. Ingestion of buckwheat resulted in anaphylaxis in almost two-thirds of buckwheat-allergic children in a study. Buckwheat ingestion resulted in anaphylaxis in 17 out of 26 children in the anaphylaxis group. Whereas, in the non-anaphylaxis group (9 out of 26 children), buckwheat ingestion resulted in acute allergic reactions such as urticaria, angioedema, and/or vomiting but not anaphylaxis. Overall, in this study, 66% of children in the buckwheat-allergic group developed anaphylaxis, 19% developed respiratory symptoms only, and 15% developed cutaneous symptoms only. None of the children developed either gastrointestinal or cardiovascular symptoms. A healthy 32-year-old Chinese woman presented with three episodes of allergic reactions after consuming buckwheat. She developed urticaria, nausea, and abdominal cramping 30 minutes later. She had a history of similar symptoms on consuming multigrain toast and buckwheat noodles. Prick testing to extracted buckwheat was significantly positive, and specific IgE to buckwheat was found, suggesting buckwheat-induced anaphylaxis. A Japanese study reported buckwheat-induced anaphylaxis in an 11-year-old boy. The boy developed generalized urticaria, persistent cough, and a hoarse voice within 60 minutes of eating buckwheat (soba) noodles, egg, broccoli, and wasabi. Also, he was using a buckwheat pillow that caused itching all over his face. A study conducted in a school in Yokohama, Japan, enrolled 92,680 children. Out of all the study children, buckwheat allergy was noted in 0.22% (140 boys and 54 girls) of children. The most prominent allergic symptoms of buckwheat allergen were urticaria (37.3%), skin itching (33.3%), and wheezing (26.5%). Anaphylaxis was observed in 3.9% of children. The incidence of anaphylaxis due to buckwheat was higher compared to egg and milk allergy. Seven students reported allergic reactions to buckwheat noodles.

Prevention And Therapy

Prevention strategies

Avoidance

Treatment of food allergy is based on avoiding causative food items after an accurate diagnosis has been established. Patients suspected of buckwheat allergy should be advised to check for common buckwheat as an ingredient while buying gluten-free food.

Cross-Reactivity

Several studies have reported cross-reactivity between buckwheat and other allergens. The common IgE antibodies between buckwheat and rice showed cross-reactivity. IgE antibodies from patients with no clinical manifestation of symptoms after ingestion of buckwheat may perceive the epitopes of buckwheat allergens, which cross-react with rice allergens. On the other hand, IgE antibodies from patients with severe symptoms after common buckwheat ingestion may bind to buckwheat-specific epitopes. The linear IgE-epitope of Fag e 2 has no known homologous epitopes except one linear IgE-epitope of Fag e 1.

The 29-kDa coconut and 19-kDa buckwheat IgE-binding bands identified may relate to the known 7S vicilin allergens, Coc n 2 and Fag e 3, respectively, indicating a strong cross-reaction between the two 7S vicilins. Cross-reactivity between the 11S globulins in buckwheat, poppy, and hazelnut has also been reported. The initial IgE inhibition experiments demonstrated that the 11S globulin in buckwheat was the primary sensitizing protein. It was concluded that 11S globulins in buckwheat potentially induced IgE antibodies that were cross-reactive with 11S globulins in other, botanically unrelated foods, which may cause anaphylactic reactions. Buckwheat also exhibits cross-reactivity with quinoa.

Common buckwheat cross-reacts with Tartary buckwheat (commonly grown and consumed in China). Clinical cross-reactivity with latex has also been observed in two patients with latex allergy who showed severe reactions to buckwheat.

The 19-kD buckwheat allergen, comprising of 135 amino acids, has been reported to have a weak homology to the vicilin-like allergens of cashew (Ana o 1), English walnut (Jug r 2), and 7 S globulin from Sesamum indicum.

Immunochemical association between salt-soluble proteins (albumins and globulins) from buckwheat and indigo seeds were demonstrated by immunoblot and immunodiffusion analyses. The bands of 24-26 kDa were found to be the significant common polypeptide groups (MCPG) between the two globulins.