# Vitamin E and Selenium Antioxidant System > Vitamin E and selenium in MBBS Biochemistry: tocopherol membrane defence, glutathione peroxidase, Keshan disease and deficiency syndromes. - Canonical URL: https://prepelephant.com/topics/mbbs/biochemistry/vitamin-e-selenium - Exam / course: MBBS · Subject: Biochemistry - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Vitamin E and Selenium Antioxidant System", PrepElephant, https://prepelephant.com/topics/mbbs/biochemistry/vitamin-e-selenium ## Direct answer Two antioxidant systems, one lipid-soluble vitamin and one trace element, share the job of stopping oxygen radicals at membranes. Alpha-tocopherol, the most active vitamin E, embeds in membranes and donates a hydrogen atom to lipid peroxyl radicals, breaking the chain reaction of lipid peroxidation; the tocopheroxyl radical it becomes is then regenerated by vitamin C at the membrane surface. Selenium operates inside the aqueous phase as selenocysteine — the twenty-first amino acid, inserted by a dedicated UGA-recoding tRNA — in the glutathione peroxidase family, thioredoxin reductases and all three deiodinases. Deficiency of either mimics the other (both end in membrane peroxidation), which is why vitamin E and selenium are taught as a pair. ## What you must remember - **Chain-breaking location:** tocopherol sits near the membrane surface, protects polyunsaturated fatty acyl chains, and is preferentially retained by the hepatic alpha-tocopherol transfer protein (alpha-TTP). - **Regeneration network:** vitamin C restores vitamin E; glutathione restores vitamin C — so antioxidant defence is a relay, not a solo performance. - **Selenoproteins with exam weight:** glutathione peroxidases (peroxide destruction, linked to GSH metabolism), thioredoxin reductase (DNA synthesis support), and the type 1, 2 and 3 iodothyronine deiodinases, which is why selenium deficiency disturbs thyroid hormone activation. - **Vitamin E deficiency states:** haemolytic anaemia of premature infants (fragile RBC membranes), malabsorption syndromes especially abetalipoproteinaemia, and AVED — ataxia with isolated vitamin E deficiency from alpha-TTP mutations, treatable with high-dose oral vitamin E. - **Selenium deficiency geography:** Keshan disease, an endemic dilated cardiomyopathy of low-selenium Chinese soil belts, aggravated by coxsackievirus; Kashin-Beck disease, an endemic osteoarthropathy of the same belts; in hospitals, long-term total parenteral nutrition without selenium. - **Indian context:** soil selenium varies widely across states, and deficiency overlaps with iodine deficiency disorders in the Himalayan belt since deiodinases are selenoproteins; RDAs are roughly 55 micrograms daily for adults (Indian values similar), with toxicity — selenosis — above about 400 micrograms per day. - **Toxicity signs:** garlic breath odour, hair loss, brittle nails, peripheral neuropathy — the mirror image of deficiency confusion that examiners enjoy. ## A premature infant, worked through A 1.4 kg neonate at three weeks of age develops a falling haemoglobin, reticulocytosis and thrombocytosis on routine screens. Preterm infants miss the third-trimester transfer of vitamin E and of selenium, and their rapidly growing tissues with high polyunsaturated fatty acid content in formula feeds make tocopherol demand spike; the result is haemolytic anaemia of prematurity, sometimes with oedema and thrombocytosis historically grouped with vitamin E deficiency. Management: enteral or parenteral alpha-tocopherol (many Indian NICUs use dl-alpha tocopheryl acetate), iron held or given cautiously since free iron is pro-oxidant, and selenium included in the parenteral nutrition trace element mix. Contrast this with an older child with chronic cholestasis or abetalipoproteinaemia: fat malabsorption wastes vitamin E into stools, and over years the deficit produces a spinocerebellar syndrome with posterior column signs and retinopathy indistinguishable from AVED — screening vitamin E levels yearly, and treating with large water-miscible doses, protects the nervous system. ## How the examiner frames it The expected pairing is "vitamin E and selenium spare each other" — animals deficient in one need more of the other, a phrase straight from Harper. Expect a mechanistic question on selenocysteine: it is encoded by UGA (normally a stop codon) redirected by a SECIS element in the 3' untranslated region, with a specific tRNA carrying selenocysteine — the cleanest example of translation-level regulation in the syllabus. A third angle is thyroid: type 1 deiodinase converts T4 to T3, so severe selenium deficiency can modestly alter thyroid function tests; conversely, iodine supplementation programmes presume adequate selenium. Quote Keshan disease by name and geography — one-line syndromic identification earns the mark. ## Frequently asked questions ### What is the chemical action of vitamin E in membranes? Alpha-tocopherol donates a hydrogen atom to lipid peroxyl radicals, terminating the chain reaction of lipid peroxidation, then is regenerated by vitamin C. ### Which amino acid carries selenium in enzymes? Selenocysteine, the twenty-first amino acid, encoded by a UGA codon recoded through a SECIS element and inserted by a dedicated tRNA. ### What is Keshan disease? An endemic, primarily dilated cardiomyopathy of selenium-deficient regions, aggravated by coxsackievirus infection, preventable by selenium supplementation. ### Which inherited disorder mimics vitamin E deficiency neurologically? AVED — ataxia with isolated vitamin E deficiency, from alpha-tocopherol transfer protein mutations, in which high-dose oral vitamin E prevents progression. ### Why does selenium status matter for thyroid hormones? All three deiodinases are selenoproteins, so selenium is required to convert T4 to active T3 and to clear reverse T3.