Sulphite sensitivity is, compared to wheat, gluten or dairy intolerances, relatively rare and occurs mainly, as Dr Janice Joneja describes below, in asthmatics. However, for those who are sulphite sensitive, it is an extremely trying condition as sulphites are used so widely in food and drink processing. And, as with most sensitivity conditions, currently the only way of managing it is to avoid contact with all sulphites.
Sensitivity to sulphites is relatively rare, except amongst asthmatics, especially asthmatics who are steroid dependent. In the US asthmatics who are sulphite sensitive could make up as much as 1% of the population. (1)
Most studies suggest that 3% to 10% of the asthmatic population may suffer symptoms if they ingest sulphite-containing additives. (2) These symptoms can occur in the lungs, gastrointestinal tract, skin, and mucous membranes. Life-threatening anaphylactic reactions to sulphites in asthmatics are not unknown but are very rare. (3)
Symptoms of sulphite sensitivity:
Management of sulphite sensitivity
Because the enzymes in the kidney and liver that are required to break down sulphites will be inadequate in those with impaired, liver and kidney function, such patients are advised to avoid sulphite. A failure to break them down will result in sulphite excess and, in due course, sulphite intolerance. (4)
There is no evidence that avoiding all sulphites improves asthma or that being exposed to sulphites poses any risk for those who are not sensitive to them. Toxicity studies in volunteers showed that consuming up to 400 mg of sulphites per day for 25 days produced no adverse effects. (5)
Diagnosis of sulphite sensitivity
Because the exact mechanism involved in sulphite sensitivity is still unknown there are no laboratory diagnostic tests available. Because sensitivity to sulphites is rarely IgE mediated, skin and blood tests are of very little help. Diagnosis is usually arrived at by a detailed history of reactions suffered after consuming sulphite-containing foods or medications.
For the diagnosis to be confirmed, an allergist may perform an oral metabisulphite challenge. This involves giving a person increasing amounts of metabisulphite to swallow, usually enclosed in gelatin capsules. Lung function and vital signs are carefully measured with each increasing dosage of the sulphite.
The typical response to sulphite is bronchospasm in an asthmatic; a significant drop in lung function confirms sensitivity to sulphites.
This test should only be performed under direct supervision of a doctor or consultant who has been trained and is experienced with such a procedure. Any other signs of a reaction to sulphite will be assessed at the same time.
What happens in sulphite sensitivity?
Nobody knows exactly what happens in sulphite sensitivity. However, research suggests several possibilities and one or all of them may play a role in sulphite intolerance.
Respiratory symptoms caused by sulphites are thought to be caused by sulphur dioxide, which acts as a direct irritant on hypersensitive airways. Sulphur dioxide is released from sulphurous acid, which forms when sulphites dissolve in water. This effect is enhanced when the sulphite is present in an acidic food. People with asthma can suffer a severe bronchospasm after inhaling as little as one part per million of sulphur.
Wheezing, flushing, and other symptoms of asthma have been caused by inhaling the vapours from a bag of dried apricots in which sulphur dioxide had been used as a preservative. (6)
IgE mediated sulphite reactions
In a few studies, sulphite-sensitive individuals have exhibited a positive skin test to sulphite which suggests an IgE-mediated reaction to the sulphite. Because the sulphite molecule is nonprotein and is too small to elicit an immunologically mediated reaction on its own, it has been suggested that sulphite acts as a hapten, combining with a protein in food to form a neoantigen that elicits antigen-specific IgE. (7)
In the process, some reports indicate that histamine and other inflammatory mediators associated with IgE-mediated allergy may be released. This provides additional weight to the idea of a possible IgE-mediated response and the potential involvement of mast cells and basophils in the process. (8) However, IgE-mediated reactions are considered to be unlikely or very rare, and no evidence of sulphite-specific IgE has been shown in research studies. (7)
Sulphite oxidase deficiency
A deficiency in the enzyme sulphite oxidase, which normally rapidly converts sulphite to sulphate, has been suggested as a possible cause of abnormally high levels of sulphites in some sensitive individuals. (2,4) Sulphates do not trigger the adverse responses associated with sulphites. However, this hypothesis has not yet been substantiated.
Use of sulphites in foods and medications
Sulphites are used as preservatives in beverages, fruits, vegetables, prepared and pre-sliced foods, and packaged snack foods. The active component is sulfur dioxide, which has been used as a preservative since Roman times, especially for wine. Today it is the most versatile food additive in use in the food manufacturing industry. Its uses include:
1. Preventing food spoilage by
2. Bleaching of flour, maraschino cherries, citrus peel before recolouring.
3. As an improving agent. Physically modifying dough by sulphitolysis of disulphite bonds in the gluten of the flour. This reduces the elasticity of the dough and reduces the time required for mixing and standing of the dough in making batches of baked goods.
4. Stabilizing vitamin C.
5. Inhibiting nitrosamine formation (e.g., in kilning of barley to make malt).
6. Sulphites are also used as preservatives in some medications, including inhalable and injectable drugs, where they act as antioxidants and prevent browning. Some forms of epinephrine (adrenaline) contain sulphite as a preservative. However, the action of epinephrine appears to overcome any adverse effects of sulphite, and administration of epinephrine in anaphylactic emergencies remains the recommended treatment.
Cooking foods does not cause sulphites to lose their effect. Nor will washing, even with a detergent, remove all traces of sulphites because they bind to several substances in foods, such as protein, starch, and sugar.
Sulphates in foods do not cause the same adverse reactions as sulphites and need not be avoided by people who are sensitive to sulphites. Table 21.1 provides examples of sources and uses of sulphites.
See below for a list of sulphite containing food and food components.
Detection of sulphites in foods
Chemically treated strips have been developed to test foods for the presence of sulphites. However, because of the high number of false-positive and false-negative results obtained with these test strips, their use is not recommended. (9)
Government regulations on the use of sulphites
Sulphiting agents or sulphites, traditionally used as food preservatives, are causing concern among consumers in all countries, and many government health departments have regulations regarding their use.
In the EU sulphites are treated as major allergens and must be declared if they exceed 10 parts per million. Similar controls exist in Australia, New Zealand and the US (10) where an FDA regulation has banned their used on fresh fruits and vegetables (with the exception of sliced potatoes and raw grapes) since 1986; a similar ban in Canada came into effect in 1987.
Canadian regulations state that “no person shall sell any fresh fruit or vegetable that is intended to be consumed raw, except grapes, if sulphurous acid or any salt thereof has been added thereto.” (11)
In the US the FDA also prohibits the use of sulphites in foods that are important sources of thiamin (vitamin B1), such as enriched flour, because sulphites destroy the nutrient.
In most countries the following ingredients may be added, at a specified level (calculated in parts per million) to certain foods and drinks, when no suitable alternatives are currently available although not all manufacturers of these products use sulphites:
These products could include:
Fruits and vegetables
However, sulphites in some food and household goods do not need to be listed – such as:
Some bulk foods
When eating in restaurants, people who are sensitive to sulphites should ask about sulphites in the foods they are offered.
Other sources of sulphites
Food-processing equipment and food packaging materials (e.g., plastic bags) may be sanitized with sulphites but these will not be listed on any labels. Sulphite-sensitives should avoid opening any packages likely to contain sulphites, especially sealed plastic bags containing dried fruits and vegetables.
Some food manufacturers publish extensive lists of their products in which they specify ingredients to which food-allergic and food-additive sensitive consumers might react. People with sulphite sensitivity are advised to check if they want to buy such foods. However, the ingredients in manufactured foods and pharmaceuticals change frequently so those with sulphite sensitivity should check the information for updates regularly.
Sulphites and thiamin (vitamin B1)
When sulphur dioxide dissolves, the disulphide chemical bonds that result break up certain protein molecules in food. Enzymes are proteins, and it is this ability of sulphites that enables it to preserve foods and prevent them browning.
However, it also has a negative effect on the food in that it destroys thiamin (13) which is essential to the nutrient value of the food.
In the US government regulations forbid the use sulphites in high-protein foods that are a significant source of thiamin, especially meat of all types, cereal grains, and milk products. (Meats may be “washed” with a sulphite solution to prevent browning, but sulphites cannot be used as an additive.)
Management of sulphite sensitivity
Avoidance is the only management strategy for sulphite sensitivity.
Sulphur dioxide (E220)
Foods likely to contain E220:
Sodium sulphite (E221)
Foods likely to contain E221-4:
Calcium sulphite (E226)
Foods likely to contain E226, E227:
First published in July 2013