Toxic risks and nutritional benefits of traditional diet on near visual contrast sensitivity and color vision in the Brazilian Amazon

•We examine how Hg, Pb, Se and omega-3 fatty acids influence vision in the Amazon.•Contrast sensitivity decreases with mercury and lead.•Contrast sensitivity improves with selenium and omega-3 fatty acids.•Color vision decreases with mercury and improves with selenium and omega-3.•Toxics and nutrients in local diet in the Amazon can influence visual function.

BackgroundVisual functions are known to be sensitive to toxins such as mercury (Hg) and lead (Pb), while omega-3 fatty acids (FA) and selenium (Se) may be protective. In the Tapajós region of the Brazilian Amazon, all of these elements are present in the local diet.ObjectiveExamine how near visual contrast sensitivity and acquired color vision loss vary with biomarkers of toxic exposures (Hg and Pb) and the nutrients Se and omega-3 FA in riverside communities of the Tapajós.MethodsComplete visuo-ocular examinations were performed. Near visual contrast sensitivity and color vision were assessed in 228 participants (≥15 years) without diagnosed age-related cataracts or ocular pathologies and with near visual acuity refracted to at least 20/40. Biomarkers of Hg (hair), Pb (blood), Se (plasma), and the omega-3 FAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in plasma phospholipids were measured. Multiple linear regressions were used to examine the relations between visual outcomes and biomarkers, taking into account age, sex, drinking and smoking.ResultsReduced contrast sensitivity at all spatial frequencies was associated with hair Hg, while %EPA, and to a lesser extent %EPA + DHA, were associated with better visual function. The intermediate spatial frequency of contrast sensitivity (12 cycles/degree) was negatively related to blood Pb and positively associated with plasma Se. Acquired color vision loss increased with hair Hg and decreased with plasma Se and %EPA.ConclusionsThese findings suggest that the local diet of riverside communities of the Amazon contain toxic substances that can have deleterious effects on vision as well as nutrients that are beneficial for visual function. Since remediation at the source is a long process, a better knowledge of the nutrient content and health effects of traditional foods would be useful to minimize harmful effects of Hg and Pb exposure.