LPI 10th ANNIVERSARY COLLOQUIUM
Vitamin E (tocopherol) is a potent fat-soluble antioxidant that must be consumed from the diet. Although vitamin E is required by humans, we donít know its specific function. We know that when there is an excess of oxidants, damage occurs to DNA, proteins, fats, and carbohydrates within our bodies, which can be partly inhibited by vitamin E. Several forms of vitamin E are made by plants, but only one form is required by the body. The alpha form remains in our blood plasma the longest, about 60 hours compared to less than 15 hours for other forms, like gamma-tocopherol. Given that all forms of vitamin E are antioxidants, understanding how the body chooses alpha-tocopherol has been a major thrust of the Traber laboratory. Our studies have shown that all of the forms are absorbed by the digestive system in the same way that dietary fats are absorbed. Then a liver protein, alpha-tocopherol transfer protein, selects forms are metabolized and excreted.
Through daily living, our bodies create reactive oxygen species (ROS). The levels of ROS increase significantly in endurance exercise and can exceed the bodyís antioxidant systems. We studied whether antioxidants would protect runners participating in an ultramarathon (50 km event) by daily administration of 300 mg of vitamin E and 1000 mg of vitamin C for six weeks before the event. Antioxidant takers compared with placebo takers had lower levels of oxidative stress markers. After the race, women recovered rapidly, while men showed elevated levels of oxidative stress throughout the recovery period. While taking vitamins E and C helped prevent oxidative damage to fats, they did not have other beneficial effects, such as faster recovery or improved inflammatory responses. We also studied vitamin E requirements in cigarette smokers who have 40% higher levels of markers of oxidative damage. Knowing the interaction of vitamin E and oxidative stress, we wanted to see whether smoking increases vitamin E requirements. We found that vitamin E disappears from the plasma about 13% faster in smokers compared to nonsmokers. We also found that higher vitamin C intakes decreased the rate at which vitamin E disappears in smokers. This is the first study in humans showing that vitamin C works to recycle vitamin E.
Our studies show that vitamin E is necessary to protect us from oxidative stress. However, estimates of nutrient intakes showed that 90% of men and 96% of women do not consume at least the estimated average requirement for vitamin E (12 mg). The recommended dietary allowance (RDA) for adults is 15 mg/day (22 IU d-alpha-tocopherol or 33 IU dl-alpha-tocopherol). In order to make sure that you consume adequate amounts of vitamin E, you should choose foods like almonds, sunflower seeds, hazelnuts, spinach, and sunflower and safflower oils. Alternatively, a multivitamin or a vitamin E pill will provide the required amount of vitamin E. Importantly, to increase vitamin E absorption from supplements, it is best to take them with food containing some fat. It is important to consume this level of vitamin E because the latest findings from a large clinical trial demonstrated that people with the highest vitamin E intakes from food had lower risks of all chronic diseases.
Last updated May 2007