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Subject: Vitamin E (Alpha-Tocopherol)
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Tocopherol is a fat-soluble vitamin with antioxidant properties; it protects cell membranes from oxidation and destruction. Vitamin E is found in a variety of foods, including oils, meat, eggs, and leafy vegetables. Serum vitamin E levels are strongly influenced by concentration of serum lipids and do not accurately reflect tissue vitamin levels. Effective vitamin E levels are calculated as the ratio of serum alpha-tocopherol per gram total lipids. Vitamin E reserves in lung tissue provide a barrier against air pollution and protect red blood cell membrane integrity from oxidation. Oxidation of fatty acids in red blood cell membranes can result in irreversible membrane damage and hemolysis. Studies are in progress to confirm the suspicion that oxidation also contributes to the formation of cataracts and macular degeneration of the retina. Because vitamin E is found in a wide variety of foods, a deficiency secondary to inadequate dietary intake is rare.
Normal range: see Table 16.85.
Evaluate neuromuscular disorders in premature infants and adults
Evaluate patients with malabsorption disorders
Evaluate suspected hemolytic anemia in premature infants and adults
Monitor patients on long-term parenteral nutrition
Evaluation of individuals with motor and sensory neuropathies
Monitoring vitamin E status of premature infants requiring oxygenation
Obstructive liver disease
Vitamin E intoxication
Malabsorption disorders, such as biliary atresia, cirrhosis, CF, chronic pancreatitis, pancreatic carcinoma, and chronic cholestasis
As previously stated, serum vitamin E levels are strongly influenced by concentration of serum lipids and do not accurately reflect tissue vitamin levels. Therefore, effective vitamin E levels are calculated as the following ratio:
Effective serum vitamin E level = alpha-tocopherol/(cholesterol + triglycerides)
A normal ratio is >0.8 mg alpha-tocopherol/gram total lipids.
For patients with normal levels of serum lipids, serum alpha-tocopherol levels provide an adequate estimate of vitamin E sufficiency. Alpha-tocopherol levels of <0.5 mg/dL (5 μg/mL) are considered deficient.
Drugs that may increase vitamin E levels include anticonvulsants (in women).
Drugs that may decrease vitamin E levels include anticonvulsants (in men).
Exposure of the specimen to light decreases vitamin E levels, resulting in a falsely low result.
Platelet tocopherol is suggested to be a better measure of vitamin E nutritional status than plasma tocopherol because it is more sensitive to vitamin E intake and is not dependent on circulating lipid levels.