Vitamin E part II

Recommended Intakes

Intake recommendations for vitamin E and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of The National Academies (formerly National Academy of Sciences) [6]. DRI is the general term for a set of reference values used to plan and assess nutrient intakes of healthy people. These values, which vary by age and gender, include:

• Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy people.
• Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
• Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects [6].

The FNB’s vitamin E recommendations are for alpha-tocopherol alone, the only form maintained in plasma. The FNB based these recommendations primarily on serum levels of the nutrient that provide adequate protection in a test measuring the survival of erythrocytes when exposed to hydrogen peroxide, a free radical [6]. Acknowledging "great uncertainties" in these data, the FNB has called for research to identify other biomarkers for assessing vitamin E requirements.

RDAs for vitamin E are provided in milligrams (mg) and are listed in Table 1. Because insufficient data are available to develop RDAs for infants, AIs were developed based on the amount of vitamin E consumed by healthy breastfed babies.

At present, the vitamin E content of foods and dietary supplements is listed on labels in international units (IUs), a measure of biological activity rather than quantity. Naturally sourced vitamin E is called d-alpha-tocopherol; the synthetically produced form is dl-alpha-tocopherol. Conversion rules are as follows:

• To convert from mg to IU: 1 mg of alpha-tocopherol is equivalent to 1.49 IU of the natural form or 2.22 IU of the synthetic form.
• To convert from IU to mg: 1 IU of alpha-tocopherol is equivalent to 0.67 mg of the natural form or 0.45 mg of the synthetic form.

Table 1 lists the RDAs for alpha-tocopherol in both mg and IU of the natural form; for example, 15 mg x 1.49 IU/mg = 22.4 IU. The corresponding value for synthetic alpha-tocopherol would be 33.3 IU (15 mg x 2.22 IU/mg).

Table 1: Recommended Dietary Allowances (RDAs) for Vitamin E (Alpha-Tocopherol) [6]

Age	Males	Females	Pregnancy	Lactation
0-6 months*	4 mg (6 IU)	4 mg (6 IU)
7-12 months*	5 mg (7.5 IU)	5 mg (7.5 IU)
1-3 years	6 mg (9 IU)	6 mg (9 IU)
4-8 years	7 mg (10.4 IU)	7 mg (10.4 IU)
9-13 years	11 mg (16.4 IU)	11 mg (16.4 IU)
14+ years	15 mg (22.4 IU)	15 mg (22.4 IU)	15 mg (22.4 IU)	19 mg (28.4 IU)

*Adequate Intake (AI)

Sources of Vitamin E

Food

Numerous foods provide vitamin E. Nuts, seeds, and vegetable oils are among the best sources of alpha-tocopherol, and significant amounts are available in green leafy vegetables and fortified cereals (see Table 2 for a more detailed list) [7]. Most vitamin E in American diets is in the form of gamma-tocopherol from soybean, canola, corn, and other vegetable oils and food products [4].

Table 2: Selected Food Sources of Vitamin E (Alpha-Tocopherol) [7]

Food	Milligrams (mg) per serving	Percent DV*
Wheat germ oil, 1 tablespoon	20.3	100
Almonds, dry roasted, 1 ounce	7.4	40
Sunflower seeds, dry roasted, 1 ounce	6.0	30
Sunflower oil, 1 tablespoon	5.6	28
Safflower oil, 1 tablespoon	4.6	25
Hazelnuts, dry roasted, 1 ounce	4.3	22
Peanut butter, 2 tablespoons	2.9	15
Peanuts, dry roasted, 1 ounce	2.2	11
Corn oil, 1 tablespoon	1.9	10
Spinach, boiled, ½ cup	1.9	10
Broccoli, chopped, boiled, ½ cup	1.2	6
Soybean oil, 1 tablespoon	1.1	6
Kiwifruit, 1 medium	1.1	6
Mango, sliced, ½ cup	0.9	5
Tomato, raw, 1 medium	0.8	4
Spinach, raw, 1 cup	0.6	4

*DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration (FDA) to help consumers compare the nutrient content of different foods within the context of a total diet. The DV for vitamin E is 30 IU (approximately 20 mg of natural alpha-tocopherol) for adults and children age 4 and older. However, the FDA does not require food labels to list vitamin E content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet. The U.S. Department of Agriculture’s (USDA’s) Nutrient Database Web site (http://www.nal.usda.gov/fnic/foodcomp/search) lists the nutrient content of many foods, including, in some cases, the amounts of alpha-, beta-, gamma-, and delta-tocopherol. The USDA also provides a comprehensive list of foods containing vitamin E: http://www.nal.usda.gov/fnic/foodcomp/Data/SR20/nutrlist/sr20w323.pdf.

Dietary supplements

Supplements of vitamin E typically provide only alpha-tocopherol, although "mixed" products containing other tocopherols and even tocotrienols are available. Naturally occurring alpha-tocopherol exists in one stereoisomeric form. In contrast, synthetically produced alpha-tocopherol contains equal amounts of its eight possible stereoisomers; serum and tissues maintain only four of these stereoisomers [6]. A given amount of synthetic alpha-tocopherol (listed on labels as "DL" or "dl") is therefore only half as active as the same amount (by weight in mg) of the natural form (labeled as "D" or "d"). People need approximately 50% more IU of synthetic alpha tocopherol from dietary supplements and fortified foods to obtain the same amount of the nutrient as from the natural form.

Most vitamin-E-only supplements provide ≥100 IU of the nutrient. These amounts are substantially higher than the RDAs. The 1999-2000 National Health and Nutrition Examination Survey (NHANES) found that 11.3% of adults took vitamin E supplements containing at least 400 IU [8].

Alpha-tocopherol in dietary supplements and fortified foods is often esterified to prolong its shelf life while protecting its antioxidant properties. The body hydrolyzes and absorbs these esters (alpha-tocopheryl acetate and succinate) as efficiently as alpha-tocopherol [6].