Relationship between microplastics in stool, diet, and inflammatory markers in healthy Japanese individuals

Abstract

Background: Exposure to microplastics (MPs) can have adverse gastrointestinal effects by inducing inflammation and oxidative stress. The types of MPs in stool vary with the dietary intake. However, how MPs in the intestinal tract influence the inflammatory cytokine levels in the gastrointestinal tract in healthy individuals remains unclear, particularly in Japan, characterized by a high intake of vegetables and seafood. In this study, we investigated the relationship between food intake, stool MPs, and inflammatory markers in healthy Japanese individuals, and estimated the sources of the stool MPs.

Methods: Twenty-two participants completed a questionnaire on daily food intake for 7 days. Thereafter, stool samples were collected to examine MP density via Fourier-transform infrared spectrophotometry. On day 8, blood samples were collected and analyzed for serum oxidative stress markers and cytokine levels. Next, the effect of total stool MP particle density (Low vs. High) on oxidative stress markers and cytokines levels was analyzed.

Results: The median total MP particle density of the participants (median age: 44 years) was 7.20 MP particles per g of stool. Seafood intake was higher in the High MP group than in the Low MP group, with a Mann-Whitney U test yielding p = 0.035 for seafood intake. However, after the false discovery rate (FDR) correction, this effect was not significant. Nevertheless, the effect size for seafood intake was large, suggesting an association with MP level. Relative to the Low MP group, the High MP group showed significantly higher thymic stromal lymphopoietin (TSLP) levels (odds ratio: 13.5; 95% confidence interval: 0.99–183, p = 0.050). The analysis further revealed that the seafood consumed by the High MP group contained significant amounts of polyethylene (PE) and polypropylene (PP), MPs commonly used in plastic packaging (PE, p = 0.028; PP, p = 0.053).

Conclusion: This study showed that stool MP particle density is likely associated with seafood intake and the TSLP level, implying that excessive MP intake may adversely affect human health. Therefore, measures to reduce MP exposure are urgently required.