The effect of Brazil nuts on selenium levels, Glutathione peroxidase, and thyroid hormones: A systematic review and meta-analysis of randomized controlled trials

Abstract

Brazil nuts or Bertholletia excelsa provide a rich natural source of magnesium, phosphorus, and manganese. Furthermore, it is rich of anti-oxidants such as selenium, vitamin E, and phenols like gallic acid and ellagic acid and have improvement effects on plasma selenium levels, Glutathione peroxidase (GPx), and thyroid hormones but the results have not been summarized in a meta-analysis. The purpose of this study is to investigate the effect of brazil nut on plasma selenium levels, GPx, and thyroid hormones. Literature search was done in MEDLINE/PubMed, Scopus and web of sciences databases up to October 2019. Studies included that had RCTs design, use brazil nut as intervention, and reported selenium levels, Glutathione peroxidase, or thyroid hormones as outcome. PRISMA guidelines followed to perform this meta-analysis and results combined using DerSimonian and Laird random effect model. Seven studies with 315 participant’s included and analyzed in this meta-analysis. Mean duration of intervention was 11 weeks and mean dosage of brazil nut was 9.42 g/day in included studies. Our study found brazil nut have significant increasing effect on plasma selenium levels (WMD: 87.63 microg/l, 95% CI: 36.02, 139.24, I2 = 98%). Furthermore, Brazil nut had increasing effect on GPx levels too (WMD: 8.05U/gHb, 95% CI:0.65, 15.45, I2 = 96%) but brazil nut had no significant effect on T3 (WMD: 0.06 pg/ml, 95% CI: −0.50, 0.39, I2 = 74%), T4 (WMD: −0.01 pg/ml, 95% CI: −0.46, 0.44, I2 = 82%), and TSH levels (WMD: 0.01 ng/ml, 95% CI: −0.03, 0.05, I2 = 0.67%).The findings of this meta-analysis indicates brazil nut increase plasma selenium and GPx levels.