SN2 SHORT NOTE 5M

Describe the functions, deficiency and clinical significance of vitamin E.

Biochemistry · 1st Professional — Pre-Clinical

Vitamin E = a group of eight tocopherols and tocotrienols; α-tocopherol is the most active.

Sources — vegetable oils (wheat germ, sunflower, safflower), nuts, seeds, green leafy vegetables
Requirement 8–10 mg/day; needs rise with polyunsaturated fat intake
Transported in lipoproteins; stored in adipose tissue and liver

The chief lipid-soluble antioxidant of the body — it sits in the membrane and terminates lipid peroxidation chain reactions
Protects polyunsaturated fatty acids of membranes and lipoproteins from free radical damage
Protects the RBC membrane — deficiency causes haemolysis
Regenerated by vitamin C after it is oxidised — the two work as a team
Spares selenium; works with glutathione peroxidase
Inhibits platelet aggregation; may protect LDL from oxidation

Rare from dietary lack alone in adults, because stores are large
Haemolytic anaemia of the newborn, especially in prematurity
Spinocerebellar ataxia and peripheral neuropathy — loss of proprioception, areflexia, ophthalmoplegia
Retinitis pigmentosa and myopathy
Causes — abetalipoproteinaemia, cystic fibrosis, chronic cholestasis, short bowel, and a rare defect of the α-tocopherol transfer protein

Nutrient	Relationship
Vitamin C	Regenerates oxidised vitamin E
Selenium	Glutathione peroxidase; the two are mutually sparing
Polyunsaturated fat	Increases the requirement — more substrate to protect
Vitamin K	Large doses of E antagonise K → bleeding risk on warfarin
Iron	Excess iron promotes the oxidation that E prevents

Given routinely to preterm infants to prevent haemolysis and retinopathy of prematurity
Large trials of vitamin E supplements for cardiovascular disease and cancer have been negative, and some suggested harm at high doses — another example of a sound mechanism failing to translate into benefit
High doses (> 400 IU/day) may increase all-cause mortality and bleeding risk
Used in abetalipoproteinaemia, where large doses prevent the neurological deterioration

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