Effects of Brazil nut consumption on selenium status and cognitive performance in older adults with mild cognitive impairment: a randomized controlled pilot trial

PURPOSE: Oxidative stress is closely related to cognitive impairment, and the antioxidant system may be a potential therapeutic target to preserve cognitive function in older adults. Selenium plays an important antioxidant role through selenoproteins. This controlled trial aimed to investigate the antioxidant and cognitive effects of the consumption of Brazil nuts, the best selenium food source. METHODS: We enrolled 31 older adults with mild cognitive impairment (MCI) who were randomly assigned to ingestion of Brazil nuts or to the control group. Participants of the treatment group consumed one Brazil nut daily (estimated 288.75 µg/day) for 6 months. Blood selenium concentrations, erythrocyte glutathione peroxidase (GPx) activity, oxygen radical absorbance capacity, and malondialdehyde were evaluated. Cognitive functions were assessed with the CERAD neuropsychological battery. RESULTS: Eleven participants of the treated group and nine of the control group completed the trial. The mean age of the participants was 77.7 (±5.3) years, 70 % of whom were female. We observed increased selenium levels after the intervention, whereas the control group presented no change. Among the parameters related to the antioxidant system, only erythrocyte GPx activity change was significantly different between the groups (p = 0.006). After 6 months, improvements in verbal fluency (p = 0.007) and constructional praxis (p = 0.031) were significantly greater on the supplemented group when compared with the control group. CONCLUSION: Our results suggest that the intake of Brazil nut restores selenium deficiency and provides preliminary evidence that Brazil nut consumption can have positive effects on some cognitive functions of older adults with MCI.