Trace Elements and Cognitive Function in Adults and Older Adults: A Comprehensive Systematic Review

Abstract Dysregulation of trace elements (TE) homeostasis can affect normal neurotransmission and lead to neurodegeneration, which frequently manifests as cognitive deterioration. Susceptibility to cognitive decline and brain diseases also increases with age, so understanding how adults and older adults can benefit or be compromised by different TE is vital. This review aims to gather, summarize, and present existing findings on the relationship and potential impact of several TE on the cognitive performance of adults and older adults. Sixty studies measured TE levels in biological samples from adults and older adults using quantitative analytical techniques, assessed cognitive performances through standardized neuropsychological tools and related the observed TE levels with the cognitive status of the same adults and older adults. Global Cognition was the most frequently studied, but specific cognitive domains such as Orientation, Attention, Learning and Memory, Language, Executive Functioning, Visuospatial and Visuoconstructive Abilities, Intelligence and Dementia Staging were also addressed. In the current literature, copper and manganese were consistently related with worse cognitive performances, both global and domain specific. The same was true for arsenic, cadmium, mercury, and lead, although these elements were not adequately assessed in relation to all cognitive domains. Selenium and zinc were consistently related to better cognitive performances, the latter displaying weaker evidence. No conclusions could be drawn for any other TE nor in relation to the Orientation or Intelligence domains. Limitations on current research are identified and future recommendations provided.