Selenium from dietary sources and motor functions in the Brazilian Amazon

► We evaluated the influence of Se on psychomotor functions, taking into account exposure to Hg and Pb. ► Elevated plasma Se is associated to better motor performances. ► Associations between Se and motor performance are stronger when taking Hg exposure into account. ► For this population with elevated Hg, high dietary Se may be critical for brain and muscle functions. ► These findings may not be applicable to populations with lower Hg and/or Se status. Selenium (Se) is a well-known anti-oxidant with a critical role in the proper functioning of nervous and muscle functions. Se deficiency has been associated with both cognitive and neuromotor impairment, while sensory and motor deficits have been attributed to excess Se. In the Lower Tapajós Region of the Brazilian Amazon, riverside populations present a wide range of Se levels. These fish-eating communities have among the highest mercury (Hg) exposures reported in the world today, and recently, lead (Pb) exposure has been identified. Some studies suggest that Se intake can be protective for Hg and/or Pb toxicity, however, data from animal and human studies are inconsistent. The objective of the present study was to examine the relations between biomarkers of Se and motor functions, taking into account co-variables and biomarkers of exposure to Hg and Pb. Participants (n=448), aged 15–87y, were recruited from 12 communities along the Tapajós River. Se concentrations were measured in whole blood (B-Se), plasma (P-Se), hair (H-Se) and urine (U-Se) by ICP-MS. Whole blood Hg (B-Hg) and Pb (B-Pb) were also measured by ICP-MS. Interview-administered questionnaires served to collect information on socio-demographics and medical history. All participants underwent a complete visual examination and performed tests of motor functions (Branches Alternate Movement Task, Santa Ana Test, Dynamometer and Grooved Pegboard Test). B-Se varied from 103 to 1500μg/L (median 228μg/L), P-Se from 53.6 to 913μg/L (median 135μg/L), H-Se from 0.4 to 3.8μg/g (median 0.7μg/g) and U-Se from 2.3 to 1375μg/g cr. (median 33.6μg/g cr.). Median B-Hg and B-Pb levels were 42.5μg/L and 113μg/L respectively. In multivariable analysis, Se biomarkers (log-transformed) were positively related to better performance on all motor tests, taking into account socio-demographic co-variables and B-Hg and B-Pb levels. P-Se consistently showed stronger associations to motor performance compared to the other Se biomarkers. Regression estimates for Se biomarke