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Uses

Observational studies that measure dietary intake and/or serum concentration, and experimental studies that ideally are randomized clinical trials (RCTs), are two means of examining the effects or lack thereof of a proposed intervention on human health. Healthcare outcomes may be expected to be in accord between reviews of observational and experimental studies. If there is a lack of agreement, then factors other than design need to be considered. In observational studies on vitamin E, an inverse correlation between dietary intake and risk of a disease, or serum concentration and risk of a disease, may be considered suggestive, but any conclusions also should rest on randomized clinical trials of sufficient size and duration to measure clinically significant results. One concern with correlations is that other nutrients and non-nutrient compounds (such as polyphenols) may be higher in the same diets that are higher in vitamin E. Another concern for the relevance of RCTs described below is that while observational studies are comparing disease risk between low and high dietary intake of naturally occurring vitamin E from food (when worldwide, the adult median dietary intake is 6.2 mg/d for d-α-tocopherol; 10.2 mg/day when all of the tocopherol and tocotrienol isomers are included), the prospective RCTs often used 400 IU/day of synthetic dl-α-tocopherol as the test product, equivalent to 268 mg of α-tocopherol equivalents.