iomarkers for vitamin status are useful because they allow intakes to be modulated to provide improved disease resistance. Without accurate and reliable biomarkers for vitamins only guesswork can be used to estimate requirements, and this has the inherent problem of increasing the risk of deficiency or toxicity. Vitamin E supplementation is safe and so excessive intakes are not detrimental to health. However, optimising intakes is advantageous because it can decrease the cost associated with supplementation. Until recently, reliable and accurate estimates of vitamin E status were unavailable or controversial. Assessment of vitamin E status through measurements of plasma tocopherol is problematic because vitamin E is stored to a great extent in adipose tissue. However, the use of α-carboxyethyl hydroxychroman (α-CEHC) has been shown in research to allow reliable estimates of vitamin E status, with regard to α-tocopherol.
For example, one study1 investigated the relationship between urinary α-CEHC and plasma α-tocopherol concentrations. These values were then related to the vitamin E intakes of the subjects using dietary surveys. The results showed that the median vitamin E intake of the subjects was 9.7 mg, which equates to 14.5 IU (to convert mg to IU divide by 0.67). These intakes were positively correlated with the urinary excretion of α-CEHC. Using statistical multiple regression analysis, urinary excretion of α-CEHC increased by 0.086 µmol/g creatinine for a 1 mg (1.5 IU) increase in α-tocopherol intake. Dietary intakes of α-tocopherol above 9 mg (13.4 IU) were needed to increase α-CEHC excretion above the plateau of 1.39 µmol/g creatinine and the inflection point at which vitamin E metabolism increased was estimated to be 12.8 mg (19.1 IU).
These results suggest that 12.8 mg is a greater than adequate intake for vitamin E, when not considering pharmacological effects. This is suggested by the increased metabolism and excretion at this value. Vitamin E supplements of 400 IU, the most common dose, therefore likely provide more than enough vitamin E for optimal vitamin E status. However, it is important to ensure intakes of all the vitamin E isomers, rather than just α-tocopherol. In another recent study2, researchers identified some novel metabolites of vitamin E that may play an important role in human metabolism. The metabolites α-CEHC glycine, α-CEHC glycine glucuronide and α-CEHC glutamine were detected and identified in the urine, faeces and plasma of human subjects and mice who were fed almonds and α-tocopherol. However, the physiological significance of these metabolites are not yet fully understood.
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