Butyrate is an important mediator of human health and disease. The mechanisms of action of butyrate are becoming increasingly well-known. Many commensal bacteria that inhabit the human gut can synthesise butyrate, which is then absorbed into the human host. Simultaneously, several immune- and inflammatory-mediated diseases are being linked to insufficient exposure to beneficial microbes from our environment, including butyrate-producing bacteria. However, the role of outdoor environmental exposure to butyrate-producing bacteria remains poorly understood. Here we review the literature on the human exposure pathways to butyrate-producing bacteria, with a particular focus on outdoor environmental sources (e.g. associated with plants, plant-based residues, and soil), and the health implications of exposure to them. Emerging evidence suggests that environmental butyrate-producers may help supplement the human gut microbiota and represent an important component of the Biodiversity and Old Friends hypotheses. Improving our understanding of potential sources, precursors, and exposure pathways of environmental butyrate-producers that influence the gut microbiota and butyrate production offers promise to advance multiple disciplines of health and environmental science. We outline research priorities to address knowledge gaps in the outdoor environment-butyrate-health nexus and build knowledge of the potential pathways to help optimise exposure to human-beneficial butyrate-producing bacteria from the outdoor environment during childhood and adulthood.

丁酸盐是人类健康和疾病的重要介质。丁酸盐的作用机理正变得越来越众所周知。居住在人体肠道中的许多共生细菌可以合成丁酸酯，然后将其吸收到人体宿主中。同时，几种免疫和炎症介导的疾病与我们无法充分接触环境中的有益微生物（包括产生丁酸盐的细菌）有关。但是，户外环境暴露于产生丁酸盐的细菌的作用仍然知之甚少。在这里，我们回顾了有关人类暴露于产生丁酸盐的细菌的途径的文献，特别关注室外环境源（例如与植物，植物残留物和土壤有关的环境源）及其暴露对健康的影响。新兴证据表明，环境丁酸盐生产者可能有助于补充人体肠道菌群，并代表了生物多样性和“老朋友”假说的重要组成部分。增进我们对影响肠道菌群和丁酸盐生产的环境丁酸盐生产者的潜在来源，前体和接触途径的了解，为推动健康和环境科学的多学科发展提供了希望。我们概述了研究重点，以解决户外环境中丁酸与健康的关系方面的知识空白，并建立潜在途径的知识，以帮助优化在儿童和成年期对户外环境中有益于人类生产丁酸的细菌的暴露。