To the editor

We read with great enthusiasm the review by Michel Burnier on the consequences of climate change and pollution for cardiovascular and kidney health.¹ This timely contribution highlights the adverse health effects of rising temperatures and pollutant exposure. We wish to extend this discussion by emphasizing a critical but underappreciated factor: the central role of the gut microbiota in mediating environmental influences on systemic disease. In parallel, we also wish to highlight the commendable efforts undertaken by leading global gastroenterology societies to address these emerging threats through research, advocacy, and sustainable health care initiatives.

Airborne pollutants—especially fine particulate matter less than or equal to 2.5 μm in diameter, polycyclic aromatic hydrocarbons, and heavy metals—disrupt the gut microbiota and compromise both epithelial and vascular integrity. A systematic review by Mousavi et al² shows that air pollution alters human gut microbial composition, increasing the abundance of inflammation‑associated taxa, such as Streptococcus and Veillonellales. These microbial shifts foster systemic inflammation and oxidative stress—key contributors to cardiovascular and chronic kidney disease (CKD). Additionally, pollutants impair intestinal barrier function, enabling translocation of endotoxins and triggering immune responses implicated in these conditions.

Beyond air pollution, environmental factors, such as diminished soil and dietary microbial biodiversity, microplastic exposure, and persistent organic pollutants, further destabilize the gut ecosystem. These disruptions lead to dysbiosis—an imbalance in microbial communities—and promote intestinal inflammation. Dysbiosis is increasingly recognized as a contributor not only to gastrointestinal disorders but also to systemic diseases, including cardiovascular and renal pathology.

Evidence from the CORDIOPREV (Coronary Diet Intervention with Olive Oil and Cardiovascular Prevention) study³ reinforces this link. In patients with coronary heart disease, specific microbial signatures and elevated postprandial lipopolysaccharide (LPS) levels predicted major adverse cardiovascular events over a 7‑year period. A microbiota‑derived risk score demonstrated prognostic value, highlighting the potential of gut profiling in secondary cardiovascular prevention.³

The gut–kidney axis is particularly susceptible to microbial alterations in the gut. A study by Laiola et al,⁴ involving 240 nondialysis CKD patients, found a progressive enrichment of bacteria producing uremic toxins—especially Hungatella and Enterocloster. These microbes generate indoxyl sulfate and p‑cresyl sulfate, metabolites linked to endothelial dysfunction, cardiovascular events, and renal fibrosis. Fecal microbiota transplantation from these patients into CKD mouse models resulted in elevated toxin levels and worsened kidney fibrosis, supporting a causal role of gut dysbiosis in CKD progression.

Microbiota alterations also play a significant role in hypertension via complex metabolic, immune, and neurohumoral mechanisms. Clinical and experimental studies show that hypertensive individuals often exhibit an altered Firmicutes / Bacteroidetes ratio, reduced microbial diversity, and lower abundance of short‑chain fatty acid (SCFA)-producing bacteria, especially those synthesizing acetate and butyrate. SCFAs exert vasodilatory and anti‑inflammatory effects, enhance regulatory T‑cell function, and suppress cytokines, such as interleukin 6 and tumor necrosis factor α. Conversely, gut‑derived metabolites, such as trimethylamine N‑oxide and LPS, contribute to endothelial dysfunction and systemic inflammation—key drivers of hypertension and atherosclerosis. The gut–visceral axes modulate blood pressure through neural, immune, and vascular pathways.

Recognizing these interconnections, in 2023, the World Gastroenterology Organization launched a 9‑part webinar series focused on the digestive consequences of climate change and offering actionable recommendations. These include reducing the carbon footprint of endoscopy, adapting dietary guidance, and encouraging clinicians to engage in environmental advocacy. In this context, we commend Michael Burnier¹ for thoughtfully proposing opportunities to reduce the carbon footprint of hemodialysis—a critical yet often overlooked area of health care sustainability. His forward‑thinking approach aligns with a broader trend across specialties toward environmentally conscious medical practice.

The United European Gastroenterology (UEG) Green Paper integrates these themes into a cohesive policy framework.⁵ It warns that climate‑related stressors may exacerbate gastrointestinal conditions, such as inflammatory bowel disease and disorders of gut–brain interaction. UEG advocates the following: 1) reducing reliance on resource‑intensive procedures; 2) adopting telemedicine and digital platforms; 3) endorsing the Planetary Health Diet; and 4) expanding interdisciplinary research on environmental determinants of digestive and systemic disease. These measures aim to mitigate the environmental impact of health care while improving long‑term patient outcomes.

In conclusion, we urge the clinical and public health communities to incorporate gut microbial ecology into the broader climate‑health paradigm. To that end, we call on medical societies, researchers, and policymakers to: 1) prioritize studies on the microbiome–environment–health axis; 2) consider incorporating microbial and barrier function markers into clinical risk models; and 3) support clean air initiatives and the development of sustainable health care infrastructure. The climate crisis is also a crisis of microbial diversity. Acknowledging the mediating role of the gut can pave the way for more integrative and effective responses toward safeguarding global health.