Objectives To study the effects of manganese (Mn) exposure and alcohol consumption on tremor.

Method Tremor was measured in 137 shipyard welders (age 39.9) and 137 referents (turner/fitters) (age 40.1) with the Catsys TREMOR. Alcohol consump­tion was assessed by measuring serum carbohydrate deficient transferrin (sCDT).

Results The geometric mean (GM) of Mn air concentration was 214μg/m³ (range 1–3230). The GM concentrations of Mn in whole blood (B-Mn) and urine (U-Mn) were 12.8μg/L and 0.36μg/g creatinine versus 8.0μg/L and 0.07μg/g creatinine in the referents. Concentration of sCDT (%) was 0.71 in welders and 0.65 in referents.

No significant differences in tremor measures were found when all welders were compared with all referents. Altogether twenty-­five subjects had sCDT above the pathological level 1.7%.

The subjects with high sCDT had increased tremor. Dominant hand: Tremor Intensity 0.21 m/s², compared to 0.15 m/s² (p < 0.001) for subjects with sCDT < 1.7%. Non-dominant hand: Tremor Intensity 0.22 m/s² vs 0.15 m/s²; (p < 0.001).

The same pattern was found when the 16 welders with sCDT ≥ 1.7% were compared with welders with sCDT values < 1.7%. The concentrations of the biological exposure indicators were similar in the welders with sCDT ≥ 1.7% compared to the other welders (B-Mn 12.8 vs 12.7 μg/L; U-Mn 0.34 vs 0.36 μg/g cr.; S-Mn 1.3 vs 1.0 μg/L).

Conclusions No effect of manganese exposure on tremor was observed, in contrast to a large effect from alcohol consumption. The results suggest that alcohol consumption can operate as a serious confounder in epidemiological studies of neurotoxicants.