Background High exposure to manganese (Mn) can cause movement disorders, but less is known if subclinical effects can occur at low doses or persist after termination of exposure.

Objectives This study aimed to investigate the effect of exposure to Mn on fine motor deficits in a prospective cohort among elderly men from an industrial area with steel production.

Methods Questionnaire-based data on occupations with exposure to Mn (mainly in the production and processing of steel) and fine motor tests were obtained in the second follow-up of the Heinz Nixdorf Recall Study (2011–2014). Occupational exposure to inhalable Mn was estimated for at-risk jobs based on 4,665 personal measurements and ancillary data on the workplaces between 1989 and 2015 compiled in the exposure database MEGA. Mn was determined in blood samples (MnB) archived at baseline (2000–2003). The study population included 1,232 men (median age 68 years). Regression models were applied to estimate the effects of working in at-risk occupations, MnB, and cumulative exposure to Mn on errors in line tracing, steadiness, or aiming and tapping hits with the non-dominant hand, adjusted for covariates.

Results Median cumulative exposure to inhalable Mn was 58 µg/m³ years in 307 men who ever worked in at-risk occupations. Exposure in the highest quartile (>185 µg/m³ years) was associated with impaired tapping and line tracing. Baseline MnB above 15 µg/L was not associated with fine motor deficits. High age, low education and current smoking predicted impaired dexterity.

Conclusion In this cohort of elderly men we found evidence that former exposure to Mn above 185 µg/m³ years may result in persistent fine motor deficits.