Dementia is one of today's greatest public health challenges. Its high socio-economic impact and difficulties in diagnosis and treatment are of increasing concern to an aging world population. In recent years, the study of the relationship between gut microbiota and different neurocognitive disorders has gained a considerable interest. Several studies have reported associations between gut microbiota dysbiosis and some types of dementia. Probiotics have been suggested to restore dysbiosis and to improve neurocognitive symptomatology in these dementias. Based on these previous findings, the available scientific evidence on the gut microbiota in humans affected by the most prevalent dementias, as well as the probiotic trials conducted in these patients in recent years, have been here reviewed. Decreased concentrations of short-chain fatty acids (SCFA) and other bacterial metabolites appear to play a major role in the onset of neurocognitive symptoms in Alzheimer disease (AD) and Parkinson disease dementia (PDD). Increased abundance of proinflammatory taxa could be closely related to the more severe clinical symptoms in both, as well as in Lewy Bodies dementia. Important lack of information was noted in Frontotemporal dementia behavioral variant. Moreover, geographical differences in the composition of the gut microbiota have been reported in AD. Some potential beneficial effects of probiotics in AD and PDD have been reported. However, due to the controversial results further investigations are clearly necessary.

中文翻译：

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肠道微生物群对最常见的神经退行性痴呆发展的影响以及益生菌对老年人的潜在影响：范围界定综述

痴呆症是当今最大的公共卫生挑战之一。其巨大的社会经济影响以及诊断和治疗的困难日益引起世界人口老龄化的关注。近年来，肠道微生物群与不同神经认知障碍之间关系的研究引起了人们的极大兴趣。几项研究报告了肠道微生物群失调与某些类型的痴呆症之间的关联。有人建议益生菌可以恢复失调并改善这些痴呆症的神经认知症状。基于这些先前的发现，本文回顾了有关受最常见痴呆症影响的人类肠道微生物群的现有科学证据，以及近年来在这些患者中进行的益生菌试验。短链脂肪酸 (SCFA) 和其他细菌代谢物浓度的降低似乎在阿尔茨海默病 (AD) 和帕金森病痴呆 (PDD) 的神经认知症状的发作中发挥着重要作用。促炎类群丰度的增加可能与两者以及路易体痴呆症更严重的临床症状密切相关。额颞叶痴呆行为变异体中明显缺乏信息。此外，AD 中肠道微生物群组成存在地域差异。据报道，益生菌对 AD 和 PDD 具有一些潜在的有益作用。然而，由于结果存在争议，显然有必要进行进一步的调查。