Do You Need Supplements?
by ADACARBOHYDRATES: How Much?; Nutrition and Performance:PART 1; Nutrition For Active Adults PART 2, Energy Needs: PART 3, Body Composition: PART 4, Carbs, Fat, Protein, REFERENCES
VITAMINS AND MINERALS
Micronutrients play an important role in energy production, hemoglobin synthesis, maintenance of bone health, adequate immune function, and the protection of body tissues from oxidative damage. They are also required to help build and repair muscle tissue following exercise. Theoretically, exercise may increase or alter the need for vitamins and minerals in a number of ways. Exercise stresses many of the metabolic pathways in which these micronutrients are required, thus exercise training may result in muscle biochemical adaptations that increase micronutrient needs. Exercise may also increase the turnover of these micronutrients, thus increasing loss of micronutrients from the body. Finally, higher intakes of micronutrients may be required to cover increased needs for the repair and maintenance of the lean tissue mass in athletes. It is assumed that the current RDAs and Dietary Reference Intakes (DRIs) are appropriate for athletes unless otherwise stated (2,68,69). Athletes at the greatest risk of poor micronutrient status are those who restrict energy intake or use severe weight-loss practices, eliminate one or more of the food groups from their diet, or consume high-carbohydrate, low-micronutrient�dense diets. Athletes participating in these types of behaviors may need to use a multivitamin and mineral supplement to improve overall micronutrient status. Supplementation with single micronutrients is discouraged unless clear medical, nutritional, or public health reasons are present, such as the supplementation of iron to treat iron deficiency anemia or folic acid to prevent birth defects.
The B-complex vitamins have 2 major functions directly related to exercise. Thiamin, riboflavin, vitamin B-6, niacin, pantothenic acid, and biotin are involved in energy production during exercise (4,70-74), whereas folate and vitamin B-12 are required for the production of red cells, protein synthesis, and in tissue repair and maintenance (75). Limited research has examined whether exercise increases the need for some of the B-complex vitamins, especially vitamin B-6, riboflavin, and thiamin (70,71,73,75,76). Available data were not sufficiently precise to set separate recommendations for athletes or to quantitatively link recommendations to energy expenditure (69). Nevertheless, the data available suggest that exercise may slightly increase the need for these vitamins perhaps up to twice the current recommended amount (72). These increased needs can generally be met by the higher energy intakes required of athletes to maintain body weight.
The antioxidant nutrients�such as vitamins A, E, and C, beta carotene, and selenium�play an important role in protecting the cell membranes from oxidative damage. Because exercise can increase oxygen consumption by 10- to 15-fold, it has been hypothesized that chronic exercise produces a constant "oxidative stress" on the muscles and other cells (77,78). In addition, muscle-tissue damage caused by intense exercise can lead to lipid peroxidation of membranes. Although there is some evidence that acute exercise may increase levels of lipid peroxide by-products (79), habitual exercise has been shown to result in an augmented antioxidant system and a reduction of lipid peroxidation (77). Thus, a well-trained athlete may have a more developed endogenous antioxidant system than a sedentary person (80). Research examining whether exercise increases the need for the antioxidant nutrients is equivocal and controversial; thus, there is no clear consensus on whether supplementation of antioxidant nutrients is necessary (77,79,80). The lack of consensus is especially true for the athlete with adequate or above-adequate blood levels of the antioxidant vitamins (77). Those athletes at greatest risk for poor antioxidant intakes are athletes following a low-fat diet, those who restrict energy intakes, or those with limited dietary intakes of fruits and vegetables.
The primary minerals low in the diets of athletes�especially female athletes�are calcium, iron, and zinc. (11,81). Low intakes of these minerals can usually be attributed to energy restriction or avoidance of animal products such as meat, fish, poultry, and dairy products. Calcium is especially important for the building and repair of bone tissue and the maintenance of blood calcium levels. Inadequate dietary calcium increases the risk of low bone mineral density and stress fractures. Female athletes are at greatest risk for low bone mineral density if energy intakes are low, dairy products are eliminated from the diet, and menstrual dysfunction is present (8,22). Vitamin D is also required for adequate calcium absorption, regulation of serum calcium levels, and promotion of bone health. The 2 primary sources of vitamin D are fortified foods, such as milk, and the production of vitamin D by ultraviolet conversion in the skin. Athletes who live at northern latitudes or who train primarily indoors throughout the year�such as gymnasts and figure skaters�may be at risk for poor vitamin D status, especially if foods fortified with vitamin D are not consumed (82). These athletes would benefit from vitamin D supplementation at the level of the DRI (5 mg/day or 200 international units [IU] vitamin D) (68).
1 2 next pageSee the full list of articles on this site.
