Clinical deficiency of vitamin E is most commonly due to severe malabsorption or abetalipoproteinemia in adults and chronic cholestatic liver disease, biliary atresia, or cystic fibrosis in children. Manifestations of deficiency include areflexia, disturbances of gait, decreased vibration and proprioception, and ophthalmoplegia.
Plasma vitamin E levels can be measured; normal levels are 0.5–0.7 mg/dL or higher. Since vitamin E is normally transported in lipoproteins, the serum level should be interpreted in relation to circulating lipid levels.
The optimum therapeutic dose of vitamin E has not been defined. Large doses, often administered parenterally, can be used to improve the neurologic complications seen in abetalipoproteinemia and cholestatic liver disease. Clinical trials to prevent cardiovascular disease and cancer have not shown beneficial effects. Several trials of supplemental vitamin E have shown slower cognitive decline in patients with Alzheimer disease. Vitamin E supplementation may also provide benefit in patients with nonalcoholic fatty liver disease.