The impact of climate, weather, seasonal transitions, and diurnal rhythms on gut microbiota and immune homeostasis.

The influence of meteorological environmental factors such as climate change, weather alterations, seasonal transitions, and diurnal cycles on human health is becoming increasingly evident, particularly through their modulation of the gut microbiome and immune homeostasis. The human gut microbiota maintains immune homeostasis and regulates various physiological and metabolic functions by producing metabolites like short-chain fatty acids (SCFAs), bile acids (BAs), indole derivatives (IDs), choline metabolites (CMs), and bacterial vitamins (BVs). Climate change disrupts this gut microbiome's impact through the gut-liver axis, which has been linked to the occurrence of fatty liver diseases. Temperature fluctuations, such as cold exposure, impair the gut microbiota's ability to respond to adaptive thermogenesis by disrupting the Firmicutes to Bacteroides ratio, affecting insulin sensitivity. In contrast, high temperatures support the increase in Proteobacterial populations, leading to greater gut permeability, allowing pathogens to trigger inflammation, oxidative stress, and immune dysregulation. In summer, an increase in Firmicutes contributes to weight gain and obesity, and in contrast, in winter, a rise in Bacteroides exacerbates conditions like rheumatoid arthritis (RA). High humidity also affects the Bacteroides/Firmicutes ratio by increasing and contributing to Bacteroides-driven inflammation. Conversely, lower humidity levels impair the mucosal defense mechanisms, increasing infection susceptibility and gut barrier dysfunction. Alterations in diurnal cycles are also linked to conditions like type 2 diabetes (T2D) and inflammatory bowel disease (IBD), by affecting the gut microbiome. Overall, the review emphasizes the crucial role of these factors in maintaining immune homeostasis through gut microbiome composition, highlighting the importance of understanding these influences for targeted interventions that restore gut health, particularly in relation to meteorologically driven environmental factors.