RBC glutathione peroxidase (GPx) measures the activity of the antioxidant enzyme glutathione peroxidase inside red blood cells. GPx is a selenium-dependent enzyme that neutralises hydrogen peroxide and lipid peroxides, protecting cells from oxidative damage. Measuring its activity in red cells provides a sensitive marker of both selenium nutritional status and overall antioxidant defence capacity.
Because GPx activity is measured over the lifespan of red cells (approximately 120 days), it reflects selenium status and antioxidant function over the preceding 3-4 months, making it more informative than plasma selenium for assessing chronic selenium adequacy. It is particularly useful in evaluating functional selenium deficiency even when serum selenium appears borderline.
FAQs
What is the relationship between selenium and GPx?
Glutathione peroxidase requires selenium (as selenocysteine) at its active site. Without adequate selenium, GPx cannot be synthesised in sufficient quantity. This makes GPx activity a direct functional measure of selenium adequacy.
Is RBC GPx better than serum selenium?
RBC GPx reflects functional selenium status over 3-4 months and is considered more clinically meaningful than a single serum selenium measurement. Serum selenium reflects recent exposure; GPx reflects whether selenium is being incorporated into functional antioxidant enzymes.
How many Brazil nuts for selenium?
Brazil nuts are exceptionally rich in selenium, with one large nut providing approximately 70-90 mcg - enough to meet the daily recommended intake of 60-70 mcg. Eating 1-2 Brazil nuts per day is a convenient and effective way to ensure adequate selenium, but eating large quantities daily is not recommended due to toxicity risk.
Can oxidative stress deplete GPx?
High levels of oxidative stress can consume GPx activity rapidly as the enzyme works to neutralise peroxides. Chronic oxidative stress from poor diet, smoking, inflammation, or metabolic disease can therefore deplete functional GPx activity even when selenium intake appears adequate.
