The Gut Microbiome Composition of Individuals with Alzheimer Disease and Related Dementia: Implications for Sub-Saharan Africa: A Systematic Review

Abstract

Background: Alzheimer’s disease (AD) and Alzheimer’s disease related dementias (ADRD) are emerging public health concerns in aging populations. Although evidence suggests that gut microbiome dysbiosis may be associated with AD, little is known about gut microbiome composition in sub-Saharan Africa, where adults aged 65+ years comprise approximately 2.7% of the population. This systematic review aimed to identify relevant studies on gut microbiota profiles in patients with AD and related cognitive conditions and to identify implications and research priorities for this region.
Methods: This systematic review was registered with PROSPERO (CRD42022354219). A systematic search of PubMed, Embase, and Scopus identified 344 records. After removal of duplicates and other ineligible records, 74 records underwent title and abstract screening, of which 22 were excluded. Fifty-two full-text reports were sought for retrieval; nine could not be retrieved, leaving 43 reports assessed for eligibility. Of these, 20 were excluded, and among the remaining 23 articles, four reviews, one opinion article, and one animal study were excluded. Seventeen original human studies met the eligibility criteria and were included in the final review.
Results: No eligible studies from sub-Saharan Africa were identified. The included studies, conducted in Asia, Europe, and North America, consistently reported differences in gut microbiome composition between individuals with AD or related cognitive conditions and cognitively healthy controls. Frequently reported alterations included increased relative abundance of Proteobacteria, Verrucomicrobia, and Actinobacteria with reduction in taxa such as Bacteroides reported in some studies. However, the specific microbial signatures varied across study populations, diagnostic categories and microbiome profiling methods.
Conclusion: Current evidence suggests that gut microbiome composition differs between individuals with AD and cognitively healthy controls, although reported microbial signatures remain heterogeneous. The absence of eligible studies from sub-Saharan Africa represents a major evidence gap. Region-specific studies are needed to determine whether gut microbiome patterns reported elsewhere are applicable to African populations and to inform future prevention, diagnostic and therapeutic research.