Objectives To explore the potential dose–response relationship between manganese (Mn) exposure and cognitive function and also plasma brain-derived neurotrophic factor (BDNF) levels in occupational Mn exposure workers.

Methods A total 819 workers were identified from our Mn-exposed workers, and 293 control workers were recruited in the same region. All exposed workers were divided into three groups based on Mn cumulative exposure index. The Montreal Cognitive Assessment (MoCA) test was applied to estimate cognitive function for all subjects. Plasma BDNF levels were determined by ELISA in 248 selected exposed workers and 100 controls.

Results Mn-exposed workers had significantly lower MoCA scores than those in the control group (25.62±0.25): those in high-exposure group had the lowest scores (21.33±0.32), compared with the intermediate-exposure group (23.22±0.30) and low-exposure group (23.57±0.23). Mn exposure levels were inversely associated with MoCA total scores, all p<0.05. A positive correlation was found between plasma BDNF levels and MoCA total scores (r=0.278, p<0.01). Moreover, compared with the control group (288.7±181.7 pg/mL), BDNF levels were lower in the high-exposure group (127.5±99.8 pg/mL), and in the intermediate-exposure (178.2±138.1 pg/mL) and low-exposure groups (223.4±178.3 pg/mL). Additionally, plasma BDNF levels decreased significantly as Mn exposure levels increased (p_trend<0.01).

Conclusions Mn exposure may be associated with decreased plasma BDNF levels and cognition impairment in this large cross-sectional study.