Understanding the difference: Sulphates vs. Sulphites
Many people confuse sulphates and sulphites, but they are different compounds with distinct roles in food. Sulphates ($SO_4^{2-}$) are salts of sulfuric acid and are widely present in nature and in the human body. Common food-grade sulphates include calcium sulphate (gypsum) and magnesium sulphate (Epsom salt), which are generally recognized as safe (GRAS) by regulatory bodies like the U.S. Food and Drug Administration (FDA). Sulphites ($SO_3^{2-}$), on the other hand, are compounds of sulfur dioxide and are primarily used as preservatives to prevent browning and inhibit microbial growth in foods and beverages.
The harmless nature of food-grade sulphates
In food, sulphates like calcium sulphate are used as firming agents, stabilizers, and nutritional supplements. Calcium sulphate is added to tofu to help it coagulate and to canned vegetables to maintain firmness. Magnesium sulphate is sometimes used to enrich mineral water and as a processing aid in fermentation. For most people, these food-grade sulphates are well-tolerated and simply metabolized by the body. Excessive consumption of some sulphates, such as magnesium sulphate, can have a laxative effect, but this is rare with typical dietary intake.
Sulphite sensitivity: the real concern
The primary reason for public concern about 'sulphur' in food stems from sulphites, not sulphates. Health authorities classify sulphites as a major allergen due to their ability to trigger adverse reactions in sensitive individuals. These reactions are not true allergies in most cases, but rather a sensitivity that can provoke asthma-like symptoms, hives, or gastrointestinal issues. It is estimated that between 3% and 10% of people with asthma may be sensitive to sulphites.
Lists of sulphites on food labels include:
- Sulphur dioxide (E220)
- Sodium sulphite (E221)
- Sodium bisulphite (E222)
- Sodium metabisulphite (E223)
- Potassium metabisulphite (E224)
- Calcium sulphite (E226)
A comparison of sulphate and sulphite safety in food
| Feature | Sulphates ($SO_4^{2-}$) | Sulphites ($SO_3^{2-}$) |
|---|---|---|
| Primary Use in Food | Firming agent, stabilizer, mineral supplement (e.g., in tofu, mineral water) | Preservative, antioxidant, anti-browning agent (e.g., in dried fruit, wine) |
| Safety for General Population | Generally Recognized as Safe (GRAS) when used at standard levels | Safe for most individuals at levels below established Acceptable Daily Intake (ADI) |
| Risks for Sensitive Individuals | Minimal to none; excessive amounts can cause laxative effects | Can trigger allergic-type reactions, especially in asthmatics, including respiratory issues, hives, or anaphylaxis |
| Labeling Requirements | Not typically required unless a functional purpose needs declaration | Must be declared on food labels if present above 10 ppm due to allergen status |
| Metabolism | Metabolized naturally by the body; excess is excreted | Oxidized by the enzyme sulphite oxidase; deficiency can lead to adverse reactions |
The foods where you find sulphites
Because of their preservative properties, sulphites are used in a variety of processed foods. Common sources include:
- Dried fruits: Apricots, raisins, and prunes are often treated with sulphites to preserve their color and shelf-life.
- Wine and beer: Both contain sulphites naturally from fermentation and can also have them added to act as preservatives.
- Pickled foods: Sauerkraut, pickles, and pickled vegetables use sulphites to prevent spoilage.
- Processed potatoes: Dehydrated potatoes, dried potato products, and some frozen french fries contain sulphites.
- Baked goods: Some biscuits and pizza crusts use sulphites as dough conditioners.
- Condiments: Sauces, gravies, and bottled lemon and lime juices can contain sulphites.
- Seafood: Some processed shrimp and shellfish may be treated with sulphites to prevent black spots.
Conclusion
While the term 'sulphate' often gets confused with 'sulphite', it is the latter that warrants attention for potential adverse reactions in sensitive people. Sulphates, like calcium and magnesium sulphate, are common, generally safe food additives. Sulphites, however, can cause significant health issues for a small, sensitive segment of the population, particularly asthmatics. Regulatory bodies mandate clear labelling of sulphites to help these individuals avoid them. For the majority of consumers, regulated amounts of both are not harmful in food. If you experience adverse reactions, consult a healthcare professional and be diligent about reading food labels.
Can food allergies start later in life? A detailed review
One study on sulphite sensitivity noted that it can develop at any point in a person's life, with some initial reactions not appearing until a person reaches their forties or fifties. This illustrates that sensitivities and allergies to food additives like sulphites can emerge unexpectedly. Individuals experiencing new symptoms should consult with a healthcare professional to identify potential triggers, which may include food additives or sulphites. The ability to manage these sensitivities is crucial for maintaining a good quality of life, and this starts with understanding and identifying the root cause.
