Selenium modifies associations between multiple metals and neurologic symptoms in Gulf states residents

Abstract

Background: Metals have been shown to have a wide range of neurologic effects across the life course, but most studies consider neurodevelopment or neurodegenerative diseases in older adults. We investigated exposure to metals during adulthood in association with subclinical neurologic endpoints, considering the metals individually and as a mixture, and potential interactions among exposures.

Methods: We measured blood levels of cadmium, lead, mercury, manganese, and selenium in 1007 Gulf state residents and estimated cross-sectional associations between ranked levels of blood metals and the presence of self-reported neurologic symptoms. Single pollutant models were mutually adjusted for other metals and we used quantile g-computation to evaluate associations with exposure to the combined mixture. In stratified analyses, we assessed heterogeneity by smoking and blood selenium.

Results: The highest quartile of cadmium was associated with a higher prevalence of central nervous system symptoms (prevalence ratio [PR] = 1.50; 95% confidence interval [CI] = 1.13, 1.99), with stronger associations among nonsmokers (PR = 1.63; 95% CI = 1.11, 2.38) and those with low selenium (PR = 2.29, 95% CI = 1.50, 3.49). Selenium also modified associations between lead and peripheral nervous system symptoms, with increased symptoms in the low selenium group at all quartiles of exposure (P-trend = 0.07). Conversely, those with the highest co-exposure to mercury and selenium had reduced neurologic symptoms (PR = 0.73, 95% CI = 0.55, 0.96). Results of the mixture analysis were consistent with single chemical results.

Conclusions: Cadmium exhibited the most consistent relationship with increased neurologic symptoms, though lead was an important exposure in subgroup analyses. Selenium may modify subclinical neurotoxic effects of metals at non-occupational levels in adults.

Keywords: Metals; Mixtures; Neurologic symptoms; Selenium.

Figure 1.

Associations between quartiles of blood cadmium, lead, and mercury and neurologic symptoms (n = 1,007). All models adjusted for sex, age, season, race, employment, alcohol, serum cotinine (ng/mL), education, income, duration of interval between enrollment and blood draw (days), and co-occurring blood metals (cadmium, lead, mercury, manganese, and selenium).

Figure 2.

Associations between quartiles of blood cadmium, lead, and mercury and neurologic symptoms among self-reported nonsmokers (n = 709). All models adjusted for sex, age, season, race, employment, alcohol, serum cotinine (ng/mL), education, income, duration of interval between enrollment and blood draw (days), and co-occurring blood metals (cadmium, lead, mercury, manganese, and selenium).

Figure 3.

A, Associations between quartiles of blood cadmium and neurologic symptoms by selenium status. All models adjusted for sex, age, season, race, employment, alcohol, serum cotinine, education, income, duration of interval between enrollment and blood draw (days), and co-occurring blood metals (lead, mercury, and manganese). B, Associations between quartiles of blood lead and neurologic symptoms by selenium status. All models adjusted for sex, age, season, race, employment, alcohol, serum cotinine, education, income, duration of interval between enrollment and blood draw (days), and co-occurring blood metals (cadmium, mercury, and manganese). C, Associations between quartiles of blood mercury and neurologic symptoms by selenium status. All models adjusted for sex, age, season, race, employment, alcohol, serum cotinine, education, income, duration of interval between enrollment and blood draw (days), and co-occurring blood metals (cadmium, lead, and manganese).