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A number of studies have compared the effects of natural source E (labeled as d-alpha-tocopherol) with synthetic E (dl-alpha-tocopherol). Their findings show that the natural version, which comes from purified plant sources, is as much as two times as effective as the petroleum-based synthetic.

To remember the difference, one expert suggests thinking of the "d" in natural source as "deliver," while synthetic's "dl" stands for "delivers less. "

The increase in RDA is good news, but many health specialists feel it's not nearly enough. Studies show that benefits from vitamin E begin at about 400 IU daily, and some experts recommend twice that amount. The upper limit for daily intake of vitamin E, set by the National Academy of Sciences, is 1,000 mg. Although amounts stated in IU - international units - have been the norm for vitamin E dosages, you may be seeing more labels with amounts in milligrams.

To avoid confusion, keep this in mind: The equivalent of the 1,000 mg upper limit is 1,500 IU of natural vitamin E or 1,100 IU of the synthetic version. So if you always take the "d" or natural form, 1,500 IU would be a daily ceiling. (Weight measurement conversions bear no relationship to efficacy of natural or synthetic E.)

Many people don't get enough vitamin E in this country partially because it's hard to meet the RDA, let alone 400 IU daily or more, through dietary sources alone.

For example, l oz of roasted filberts, a relatively high source of the nutrient, contains less than 11 IU; 1 cup of boiled spinach contains less than 4 IU. You do the math, then take your supplements.

"Dietary Reference Intakes (DRIB) for vitamins C and E, selenium and carotenoids" Published April 11, 2000, by the Food andNutrition Board, Institute of Medicine and National Academy of Sciences.