Explain the Bioavailability of Vitamin E?
For dietary purposes, vitamin E activity is expressed as a-tocopherol equivalents (a-TEs). One α-TE is the activity of l mg α-tocopherol. To estimate the α-TE of a mixed diet containing natural forms of vitamin E, the number of milligrams of β-tocopherol should be multiplied by 0.5, y-tocopherol by 0.1, and a- tocopherols by 0.3. The bioavailability of tocopherols varies inversely with the uptake. This means that ingesting four times the amount of the vitamin raises tissue levels by only two-fold.
A high correlation exists between the total fat and tocopherol concentrations in blood serum. Thus, diseases associated with high serum lipids (hypothyroidism, diabetes, hypercholesterolemia) produce high plasma vitamin E levels and those associated to low serum lipids (abetalipoproteinemia-a genetic disorder that interferes with the normal absorption of fats and fat-soluble vitamins, malnutrition, cystic fibrosis) produce low vitamin E levels.