VITAMIN E


Vitamin E refers to a family of eight related fat-soluble compounds known as the tocopherols and the tocot- rienols. Like vitamin C, vitamin E is well known for its antioxidant function in preventing free radical damage to cell membranes.Vitamin E also plays a role in immune function.9


Dietary vitamin E intakes in


athletes are generally low compared with the intake of other antioxidants. Researchers have reported that vitamin E intakes were lower than intake of other antioxidants in female figure skaters and heptathletes as well as male and female rowers.33,34 Although athletes have reported low dietary intakes of vitamin E, supplementation may be benefi- cial by reducing exercise-induced oxidative stress.14


Garelnabi and colleagues sought to determine how vitamin E supplementation affects VO2 max, oxidative stress, and lipid profile during short-duration,


moderate-intensity activity. In the study, 455 healthy participants were randomized into two groups— placebo or vitamin E supplemented with 800 IU—and engaged in moderate aerobic exercise for at least 30 minutes per day, three times a week for 8 weeks. Te researchers determined that myeloperoxidase (MPO), a protein released aſter oxidation of low-density lipoprotein cholesterol, increased in both the supplemented and placebo groups following the exercise regimen. MPO levels generally drop to clini- cally normal levels over time aſter oxidative stress; however, the vitamin E–supplemented participants had MPO concentrations that remained high aſter the 8-week intervention. Te researchers had hoped to ascertain information regarding mitochondrial changes in skeletal muscle in the supplemented and nonsupplemented participants.35 Antioxidant combination therapies are frequently tested to assess the additive effects. Bryant and


colleagues examined different levels and combinations of antioxidant supplements in seven trained male cyclists (approximately 22 years old) who participated in four separate supplementation phases. They ingested two capsules per day containing the following treatments: placebo (placebo plus pla- cebo), vitamin C (1 g/day of vitamin C plus placebo), vitamins C and E (1 g/day of vitamin C plus 200 IU/kg of body weight of vitamin E), and vitamin E (400 IU/kg of vitamin E plus placebo). Researchers found that the vitamin E treatment was more effective than vitamin C alone or vitamin C and vita- min E together. Plasma malondialdehyde concentrations, a general measure of oxidative damage, were lowest with the vitamin E supplementation.36 Te effects of vitamin E supplementation on resistance training performance are still unknown. Avery


and colleagues assessed the effects of 1,200 IU/day of vitamin E vs a placebo on the recovery responses to repeated bouts of resistance training. No significant differences were found between the group taking the vitamin E supplement and the placebo group in muscle soreness, exercise performance, or plasma malond- ialdehyde concentrations.37


Te role of vitamin E in preventing oxidative damage due to exercise may be


significant. Long-term research is needed to assess vitamin E supplementation on oxidative stress from exercise. Dietary sources of vitamin E are listed in Table 5.2.


VITAMIN A


Vitamin A, considered a subset of retinoids, is a fat-soluble vitamin best known for the role it plays in the visual cycle.17


duction, gestation, fetal development, and bone formation; it also serves as an antioxidant.17,38


Other important functions of vitamin A include its roles in cellular differentiation, repro- Plants can


synthesize carotenoids, which can serve as precursors of vitamin A; however, humans and other animals convert carotenoids to retinol or acquire preformed vitamin A from animal foods or supplements.17


Assess-


ment of vitamin A intake in people who are physically active has shown varied results, likely because the source of vitamin A (plant vs animal) was not specified.14 Vitamin A antioxidant status may alleviate the oxidative load associated with endurance training.


Braakhuis and colleagues analyzed how antioxidant intake, including that of vitamin A, and training sta- tus affect total antioxidant capacity (TAC) in competitive rowers. TAC measures how well a food product or biological sample can reduce an oxidant and is measured by the moles of radicals neutralized per gram of tested sample. Te researchers found that blood TAC was correlated with total dietary antioxidant intake


86 SECTION 1: SPORTS NUTRITION BASICS


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