Low-dose ionizing radiation and cognitive function: evidence, mechanisms, and controversies.

Humans are chronically exposed to ionizing radiation. Natural background radiation is generally harmless, yet potential risks arise from nuclear accidents, accidental medical irradiation, and high-background-radiation regions. The effects of high-dose radiation are well established, whereas research on low-dose ionizing radiation (LDIR, ICRP-defined as doses below 100 mSv) remains limited and highly controversial. As the most prevalent exposure type, LDIR originates from medical imaging, occupational exposure, and environmental background radiation. Previous studies have largely focused on its neurotoxicity, implicating neuroinflammation, oxidative stress, and synaptic damage. Nevertheless, emerging evidence indicates that LDIR administered at specific doses and regimens may exert neuroprotective effects via hormesis: it reduces Aβ deposition, promotes anti-inflammatory microglial polarization, and enhances hippocampal neurogenesis, thereby ameliorating cognitive impairment. Constrained by ethical considerations, sample size limitations, and inter-model variability, no consensus has been reached regarding its dual mechanisms, safety thresholds, and long-term outcomes. This review systematically synthesizes studies published over the past five years, integrating both detrimental and protective effects and identifying key modulating factors (radiation parameters, biological characteristics, and socioeconomic variables). Importantly, we also discuss the translational potential of LDIR in clinical settings, summarize current evidence, and highlight barriers to implementation. By examining preclinical data and prospective clinical applications, this review provides a theoretical framework for refining radiation protection standards and developing non-pharmacological interventions for cognitive disorders, filling critical knowledge gaps in this field.