vitamin E

Vitamin E consists of tocopherols and tocotrienols, with alpha-tocopherol being the most biologically active form. As a lipid-soluble antioxidant located in cell membranes, it prevents lipid peroxidation of polyunsaturated fatty acids, protecting erythrocyte membranes and other cells from oxidative damage caused by free radicals, particularly important in tissues exposed to high oxygen concentrations (e.g., retina, lungs of premature infants).

Absorption requires bile acids and pancreatic enzymes for micelle formation, similar to other fat-soluble vitamins (A, D, E, K), and it is transported in chylomicrons and VLDL. Deficiency can result from fat malabsorption syndromes such as cystic fibrosis, cholestatic liver disease, abetalipoproteinemia, or chronic pancreatitis, since vitamin E absorption is dependent on normal fat digestion and lipoprotein transport.

Clinical manifestations of deficiency include: - Hemolytic anemia in premature infants due to fragile erythrocyte membranes susceptible to oxidative damage - Spinocerebellar ataxia, areflexia, and loss of position/vibration sense due to degeneration of posterior columns and spinocerebellar tracts - Peripheral neuropathy - Skeletal muscle myopathy

This neurologic presentation clinically mimics vitamin B12 deficiency (subacute combined degeneration) but is distinguished by the absence of megaloblastic anemia and normal methylmalonic acid levels.

Toxicity (rare, usually from supplementation) can inhibit vitamin K-dependent clotting factor activation, increasing bleeding risk, especially in patients on anticoagulants like warfarin.

High-yield associations: abetalipoproteinemia (autosomal recessive, MTP gene mutation causing inability to form chylomicrons, leading to fat-soluble vitamin deficiencies including vitamin E, with acanthocytosis and retinitis pigmentosa), and vitamin E as a potential antioxidant therapy studied (with mixed results) in various oxidative stress-related conditions.