Always consult a doctor before starting any supplement
GPX was measured adding cell extract to 50 mmol/l potassium phosphate pH 7.0 containing 1 mM EDTA, 1.5 mM sodium azide, 0.15 IU of purified glutathione reductase from bakers' yeast, 0.45 mM GSH, 0.2 mM NADPH, 1.2 mM cumene hydroperoxide One unit of GPX was defined as the amount of enzyme which produces 1 mol of GSSG (oxidized glutathione)/min at 25C
While some foods like plant-based milks and cereals are fortified with B12, relying on them isnt always enough to meet your bodys needs
Vomund S, Schfer A, Parnham M, Brne B, von Knethen A
Biochem Biophys Res Commun 184(1):212-6, 1992
doi:10.1016/j.fertnstert.2018.11.048