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| Bioavailability of vitamin E - Vitamins and Minerals Vitamin E has been controversial since its discovery in the 1920s. Only a-tocopherol has been shown to reverse human vitamin E deficiency symptoms, although there are other forms of vitamin E. Recently, the potential antioxidant activity of vitamin E has gained attention in the nutrition industry. continued below... |
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Vitamin E is being investigated for potential benefit in chronic diseases such as heart disease and Alzheimer's disease. However, studies concerning vitamin E have been inconsistent. This lack of consistency led to the hypothesis that the bioavailability of supplemental vitamin E is highly dependent on the way in which the supplement is consumed--and it is in fact highly influenced by the prandial status in humans.
This hypothesis led to a trial to compare supplements with vitamin E-enriched foods. Vitamin E-fortified, ready-to-eat breakfast cereals are a major food source of a-tocopherol in the American diet. Therefore, using stable-isotope-labeled a-tocopherol, researchers tested whether encapsulated vitamin E consumed with fat-free milk was as effective in raising plasma a-tocopherol concentrations as was vitamin E-fortified, wheat-based cereal eaten with fat-free milk. The doses used were equivalent to the US recommended dietary allowance for vitamin E (30 IU) or those in a typical vitamin E supplement (400 IU).
Vitamin E bioavailability was evaluated using deuterium-labeled all-rac-a-tocopherol in three 4-day trials which were held 2 weeks apart. The five fasting subjects consumed the following in sequence with 236 ml fat-free milk: 400 IU a-tocopherol capsule, 41 g ready-to-eat cereal containing 30 IU a-tocopherol, and 45 g cereal containing 400 IU a-tocopherol. Five months later, the subjects consumed a 400-IU capsule with 41 g of vitamin E-free cereal. Blood was obtained up to 72 hours after the beginning of each trial.
The mean ([+ or -] SD) vitamin E bioavailabilities of the 30-IU cereal and the 400-IU cereal were 6 [+ or -] 2 and 26 [+ or -] 8 respectively, times the vitamin E bioavailability of the 400-IU capsule. The areas under the 0 hr to 72 hr a-tocopherol curves for the 400-IU capsule, the 30-IU cereal, and the 400-IU cereal were 30 [+ or -] 7 [micro]mol x hr/l, 153 [+ or -] 43 [micro]mol x hr/ l, and 765 [+ or -] 164 [micro]mol x hr/l (all trial comparisons, P<), respectively. In trial four, 3 subjects barely responded and 2 subjects had areas under the curve that were similar to their 400-IU cereal responses.
The low bioavailability of vitamin E from the 400-IU capsule, and the variability observed when the capsule was consumed with cereal, suggest that encapsulated vitamin E is poorly absorbed when consumed with a low-fat meal. It appears that bioavailability can be enhanced by food fortification with vitamin E.
S. Leonard, C. Good, E. Gugger, et al. Vitamin E bioavailability from fortified breakfast cereal is greater than that from encapsulated supplements. Am. J. Clin. Nutr. 79:86-92 (January 2004) [Correspondence: MG Traber, Linus Pauling Institute, 571 Weniger Hall, Oregon State University, Corvallis, OR 97331. E-mail: .]