underreport energy intake in national surveys, and fat intake is more underreported than energy intake in the NHANES III survey (Brief-el et al., 1997). Since vitamin E is associated with fat in the food matrix, underreporting of the total intake of fat also results in the underreporting of vitamin E intake. Furthermore, there are uncertainties in the amount of α-tocopherol in fats and oils consumed, particularly when food labels do not provide the specific fat or oil used (e.g., “this product may contain partially hydrogenated soybean and/or cottonseed oil or vegetable oil”); in addition, because of the small number of samples, the vitamin E content of the foods in the Continuing Survey of Food Intake of Individuals (CSFII) and NHANES III databases are very variable (J. Holden, Agricultural Research Service, U.S. Department of Agriculture, personal communication, April 13, 1999). Finally, the amounts of fats and oils added during food preparation (and absorbed into the cooked product) is difficult to assess using diet recall methodologies, yet may contribute substantially to vitamin E intake.
The UL for α-tocopherol for adults is 1,000 mg/day of all eight stereoisomers of α-tocopherol. This UL is based on the intake of α-tocopherol from supplements only, because there is no evidence of adverse effects from the consumption of vitamin E naturally occurring in foods. In addition, the UL was based on animal studies feeding either RRR-α-tocopherol (natural vitamin E) or all rac-α-tocopherol (synthetic vitamin E), both of which had equivalent adverse effects. Although adults should not exceed the UL of 1,000 mg/day of any form of supplemental α-tocopherol, intakes above this amount may be appropriate for investigation in well-controlled clinical trials.
Sources of vitamin E available as supplements are usually labeled as international units (IUs) of natural vitamin E and its esters or as synthetic vitamin E and its esters. Table 9-1 shows the IUs of various sources of supplemental vitamin E that are equivalent to the UL for adults of 1,000 mg/day of any form of supplemental α-tocopherol.
Because the various forms of vitamin E are not interconvertible in humans, it is recommended that nutrient databases be specific enough to identify and report α-tocopherol intake separately from intake of other tocopherols. However, until this is done, it is possi-