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Sulphites get a bad rap, but the preservative isn't as bad as you think

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The negative stigma that sulphites get should be weighed against its value as a preservative.

QUESTIONI used to enjoy snacking on dried apricots, but then I started getting ulcers in my mouth that only went away when I stopped eating them. I understand dried apricots are often treated with sulphites, so I concluded that was the problem. However, after eating walnuts, I again got ulcers in my mouth. Are nuts also being treated with sulphites? 

ANSWER: The benefits of sulphites have been known since the ancient Greeks and Romans used them to preserve wine.

In the 21st century, we still use sulphites to prolong the shelf life of food and drinks. They maintain flavour and colour, inhibit bacterial growth, reduce spoilage and stop produce from spotting or turning brown.

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Unfortunately, a small percentage of people are sensitive to sulphites, particularly asthmatics, of whom 5-10% are affected. Sulphites release the gas sulphur dioxide, which can cause the airway to become irritated and constricted, resulting in wheezing, chest tightness and coughing. This is not a response of the immune system and is not an allergic reaction.

Unfortunately, standard blood or skin-allergy testing will not identify a sensitivity to sulphites, and a food exclusion and reintroduction diet may be required.

Allergic reactions to sulphites are extremely rare, but can cause life-threatening anaphylaxis for which an injection of adrenaline is required.

Sulphites can be naturally present in food as well as being used as a food additive in everything from dried apricots and grapes to cordial, beer and wine.

In your case, you’ve noted that mouth ulcers occur after a period of eating either dried apricots or walnuts.

However, mouth ulcers are unlikely to be sulphite-induced, according to Dr Vincent St Aubyn Crump, an allergy specialist and author of Allergies: New Zealand’s Growing Epidemic. “Sulphites are in dried fruits and found naturally in peanuts, but not really tree nuts, and they usually cause respiratory symptoms. Mouth ulcers aren’t likely.”

Having said that, although tree nuts don’t naturally contain sulphites and aren’t treated with them, there may be potential for cross-contamination of nuts stored in bulk bins if the bins have also been used for dried apricots, for example.

The cause of recurrent mouth ulcers is often a mystery, says Crump. “There are several theories, of course, and stress is one. Depending on the severity, inflammatory bowel disease is a possibility. It is very rare that a specific food or food additive is the cause.”

It’s natural for us to presume a food is causing symptoms in our mouth or elsewhere in our gastrointestinal tract, but this is often disproved by blinded challenges using the suspect food.

The only treatment for sulphite sensitivity is to avoid foods and drinks that have them. Fortunately, by law, the presence of sulphites in food must be indicated on the label by code numbers 220 to 228 or the word “sulphite”.

In February, Food Standards Australia New Zealand (FSANZ), after reviewing the levels of sulphites in our food supply, advised that there was a potential for some children to exceed the current acceptable daily intake (ADI) for sulphites if they were high consumers of certain foods.

However, the review also noted that the ADI for sulphites, set in 1974, may be flawed and it is unlikely that current levels of sulphites in food pose a risk to consumers.

But if you are concerned, FSANZ recommends you limit foods that are high in sulphites such as cordials, dried fruit and sausages.  

This article was first published in the May 11, 2019 issue of the New Zealand Listener.