Folate is a B-vitamin with an important role in health and disease. The optimal folate status with regard to human health remains controversial. A low intake of natural folate as well as excessive intake of synthetic folic acid, were previously linked to an increased risk of colorectal cancer or with aberrant molecular pathways related to carcinogenesis in some studies. Importantly, most studies conducted so far, solely focused on dietary intake or circulating levels of folate in relation to cancer risk. Notably, diet or dietary supplements are not the only sources of folate. Several bacteria in the gastrointestinal tract can synthesize B-vitamins, including folate, in quantities that resemble dietary intake. The impact of bacterial folate biosynthesis concerning human health and disease remains unexplored. This review highlights current insights into folate biosynthesis by intestinal bacteria and its implications for processes relevant to cancer development, such as epigenetic DNA modifications and DNA synthesis. Moreover, we will reflect on the emerging question whether food-grade or intestinal bacteria can be considered a potential target to ensure sufficient levels of folate in the gastrointestinal tract and, hence the relevance of bacterial folate biosynthesis for disease prevention or treatment.

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叶酸细菌的生物合成和结直肠癌的风险：不仅仅是肠胃的感觉。

叶酸是一种B族维生素，对健康和疾病具有重要作用。关于人类健康的最佳叶酸状况仍存在争议。在某些研究中，天然叶酸的摄入量低以及合成叶酸的摄入量过高与结直肠癌的风险增加或与致癌作用有关的异常分子途径有关。重要的是，迄今为止进行的大多数研究仅关注饮食摄入量或与癌症风险相关的叶酸循环水平。值得注意的是，饮食或膳食补充剂不是叶酸的唯一来源。胃肠道中的几种细菌可以合成B-维生素（包括叶酸），其数量与饮食摄入量相似。叶酸细菌生物合成对人类健康和疾病的影响尚待探索。这篇综述重点介绍了肠道细菌对叶酸生物合成的最新见解及其对与癌症发展相关的过程的影响，例如表观遗传学DNA修饰和DNA合成。此外，我们将反思一个新出现的问题，即食品级或肠道细菌是否可以被视为确保胃肠道中叶酸水平足够的潜在目标，从而确保细菌叶酸生物合成与疾病预防或治疗的相关性。