Cobalt internal exposure and risk of cognitive impairment among older adults: A national prospective cohort study.

Despite Cobalt (Co) presents a paradox due to its role in vitamin B12 and potential neurotoxicity, the effects of low-level exposure on cognition function in older adults remain unclear. This study recruited a total of 11,338 participants aged ≥ 60 from two cohorts and followed them for a maximum period of 7.8 years (mean: 4.0 years) between 2017 and 2024. Baseline blood and urine Co levels were measured by inductively coupled plasma-mass spectrometry, and cognitive function was periodically assessed using the Mini-Mental State Examination. After excluding participants with missing Co measurements, loss to follow-up, or baseline cognitive impairment, 6868 participants for blood Co and 6584 participants for urine Co were included for analysis, respectively. Cox proportional hazards models estimated HRs (95% CIs) across Co quartiles and per interquartile-range (IQR) increase. During follow-up, 1141 (16.6%) developed cognitive impairment. Each IQR increase in blood Co was associated with a 19.6% higher risk of incident cognitive impairment. Participants in the highest blood Co quartile had a 65.6% greater risk versus Q1 (Adjusted HR 1.656; 95% CI 1.366-2.008). For specific cognitive domains, higher blood Co levels were significantly associated with poorer performance in recall (β=-0.061, 95% CI: -0.091, -0.031), and attention and calculation (β=-0.032, 95% CI: -0.061, -0.003). Restricted cubic spline analysis revealed a significant linear dose-response relationship and the association was stronger in adults aged ≥ 80 years. Urinary Co yielded similar associations. This prospective cohort study in Chinese older adults indicates that Co exposure is associated with increased cognitive impairment risk. These findings can inform the development of novel preventive strategies to improve cognitive health in the context of rapid population aging.