Sulfites and the gut: a dangerous relationship? When wine means joy and health

Initial note: this article was previously published and has been updated according to scientific and divulgative criteria. The information provided here is for informational purposes only and does not replace the advice of a doctor or healthcare professional. For clinical questions or health problems, always consult a specialist.

IN BRIEF

• Sulfites (sulfur dioxide and salts like metabisulfites/bisulfites) are preservatives used in wine and food to limit oxidation and microbial growth.
• In vitro studies show that sulfite concentrations can inhibit the growth of some beneficial bacteria commonly considered probiotics; this evidence does not automatically prove negative effects in the human gut at normal consumption levels.
• There are experiments indicating sulfites' ability to degrade or reduce the availability of thiamine (vitamin B1) in certain experimental contexts.
• Some people with asthma may have adverse reactions to beverages or foods rich in sulfites; the mechanisms are still being investigated, and prevalence is limited to sensitive subgroups.
• Practical decisions on wine choice and diet should balance enological quality, consumption context, and individual conditions (asthma, known sensitivity, overall diet).

Abstract: what does science say?

Simple definition: "sulfites" include sulfur dioxide (SO2) and its salts; in enology and the food industry, they are used as antioxidants and antimicrobials to preserve color, flavor, and safety. Available evidence includes both in vitro experimental data and clinical and observational studies on adverse reactions in subgroups of people.

Experimental evidence shows that, at certain concentrations, bisulfite salts can inhibit the growth of bacterial species considered beneficial in laboratory models. Other in vitro studies indicate that sulfurous salts can react with thiamine and decrease its availability under controlled conditions. Clinically, some asthmatic individuals may experience bronchospasm or respiratory symptoms in response to high-sulfite beverages, while the general population shows little documented sensitivity.

What depends on dose and context: observed effects vary greatly with concentration, exposure time, chemical form (free or bound SO2), pH, and food/beverage conditions. Many in vitro studies use higher concentrations or different conditions than those found in the gastrointestinal tract after moderate consumption.

Interpretive limits: the translation from culture results to clinical impact is uncertain; experimental studies do not automatically demonstrate harm in humans at consumer-compatible levels. It is therefore necessary to read the evidence with caution and distinguish biological plausibility from proof of systemic harm.

Definition and main functions

Sulfites are molecules with antioxidant and antimicrobial roles: in wine, they serve to prevent oxidation, control undesirable fermentations, and limit the growth of contaminating microorganisms. Their presence can be natural (produced by yeasts) or due to additions during winemaking. In enology, the balance between product protection and residual quantity is managed according to the type of wine and production practices.

What kind of evidence exists

The literature is composite: in vitro experiments on single microbial species, enological studies on the antimicrobial role of SO2 during fermentation and aging, and clinical or provocation studies on sensitive subjects (e.g., asthmatics). These different types of work are useful but do not equate to unequivocal proof of systemic harm for the average consumer.

What it means in practice

Biological significance: microbiology studies show that sulfite salts like sodium bisulfite can directly reduce the growth of specific species of Lactobacillus and Streptococcus used as indicators of "beneficial" bacteria in culture experiments; these results provide biological plausibility for a possible antimicrobial effect of sulfites beyond their technological role [1].

Thiamine availability: recent and older experimental research indicates that sulfurous agents can react with thiamine or decrease its quantity in test systems, with evidence that depletion is observed under controlled experimental conditions and in some food technological processes; this suggests a potential interaction between sulfites and vitamin B1, especially at high levels or in particular matrices [2][3].

Impact on pathogens and microbial flora: the microbicidal activity of sulfites is not limited to "bad" bacteria — effects have also been observed in the laboratory on pathogenic microorganisms like Helicobacter pylori — but sensitivity is species-dependent and conditioned by pH and chemical form [4].

Individual reactions and asthma: controlled clinical trials show that a proportion of patients with a history of asthma may experience bronchospasm or symptoms after challenge with high-sulfite wines; this is a real phenomenon but limited to sensitive individuals, not the general population [5].

Effects on wine and nutritional implications: the addition of SO2 modifies the metabolic profile of wine and interacts with phenolic compounds and indoles; these reactions are important for sensory quality and technological management, but do not automatically imply a systemic nutritional risk for those who consume wines moderately [6][7][8].

KEY POINTS TO REMEMBER

• Sulfites are useful in enology and the food industry for preservation and microbiological control; their presence is regulated at the production level.
• In vitro evidence shows that, at certain concentrations, sulfites can inhibit bacteria considered beneficial, but the translation to human clinical effects requires further research [1].
• Some experiments indicate that sulfites can reduce thiamine availability under specific conditions; this is relevant in technological contexts or high exposures [2][3].
• Individuals with known asthma or previous reactivity to sulfites may experience respiratory reactions after consuming sulfite-rich foods/beverages; consult a specialist if symptoms occur [5].
• For most people, moderate consumption of quality wine is not associated with clear evidence of intestinal harm from sulfites; however, production practices (organic, natural, low- or no-added sulfite wines) can reduce residual exposure.

Limitations of the evidence

Fundamental difference between types of studies: many of the most cited observations come from in vitro experiments (bacterial cultures, growth systems) or enological studies; such results show possible mechanisms but do not automatically provide evidence of a clinical effect in humans. A laboratory result is useful for hypothesizing but not for confirming a health risk at the population level [1].

Methodological limitations: experimental parameters (concentration, exposure duration, pH, matrix composition) often differ significantly from the conditions of real food or beverage consumption. For example, concentrations used in culture to observe bactericidal effects may be higher than those that reach the colon after normal ingestion. Furthermore, the complexity of the human gut microbiota is not replicable in simple culture.

Context variability: effects observed in one type of wine or food are not automatically generalizable to others. Individual nutritional status, overall diet, the presence of clinical conditions (e.g., severe asthma), and concomitant drug use influence the response to preservative compounds.

Need for caution: well-designed clinical studies and in vivo research are needed to quantify real exposures, monitor changes in the integrated microbiota, and evaluate relevant clinical outcomes before drawing definitive conclusions about systemic risks.

Editorial conclusion

Sulfites have a long history of use and a clear technological function in enology and the food industry. Experimental research highlights plausible mechanisms for effects on the microbiota and interactions with vitamins like thiamine, but the body of evidence does not justify generalized alarm. For the general population, moderate wine consumption is not proven to be a direct cause of systemic intestinal harm, while for sensitive subgroups (e.g., some asthmatics), caution and specialist evaluation are advisable. The choice of low-sulfite wines or certified products can be a reasoned preference, not a health prescription. Finally, clinical and population studies are needed to clarify how and to what extent in vitro evidence translates into real risks.

Editorial note

The article has been updated with bibliographic and scientific integrations and written according to transparency and verifiability criteria. The scientific research listed below includes peer-reviewed studies with verifiable DOIs. This content is not intended to replace individual medical evaluations.

SCIENTIFIC RESEARCH

1. Irwin SV, Fisher P, Graham E, Malek A, Robidoux A. Sulfites inhibit the growth of four species of beneficial gut bacteria at concentrations regarded as safe for food. PLoS One. 2017 Oct 18;12(10):e0186629. https://doi.org/10.1371/journal.pone.0186629
2. Mooney R, Giammarini E, Corbett E, et al. Sodium Metabisulfite Inhibits Acanthamoeba Trophozoite Growth through Thiamine Depletion. Pathogens. 2024 May;13(6):431. https://doi.org/10.3390/pathogens13060431
3. Thiamine destruction by sodium bisulfite in infusion solutions. Am J Hosp Pharm. 1981 Dec;38(12):1911–1913. https://doi.org/10.1093/ajhp/38.12.1911
4. Hawrylik SJ, Wasilko DJ, Haskell SL, Gootz TD, Lee SE. Bisulfite or sulfite inhibits growth of Helicobacter pylori. J Clin Microbiol. 1994 Mar;32(3):790–792. https://doi.org/10.1128/jcm.32.3.790-792.1994
5. Vally H, Misso NLA, Thompson PJ. Role of sulfite additives in wine induced asthma: single dose and cumulative dose studies. Thorax. 2001 Oct;56(10):763–769. https://doi.org/10.1136/thorax.56.10.763
6. Regueiro J, et al. The impact of SO2 on wine flavanols and indoles in relation to wine style and age. Sci Rep. 2018;8:13760. https://doi.org/10.1038/s41598-018-19185-5
7. Stone E, et al. Sulfur dioxide treatment alters wine microbial diversity and fermentation progression in a dose-dependent fashion. Am J Enol Vitic. 2014;(Article). https://doi.org/10.5344/ajev.2014.14096
8. Author(s). Impact of acetaldehyde- and pyruvic acid-bound sulphur dioxide on wine lactic acid bacteria. J Appl Microbiol. 2011. https://doi.org/10.1111/j.1472-765X.2011.03193.x