[Marc Nelson Chocolate Mood (1999) Retail Cd
Rapheal Charlton
This fact sheet provides an overview of selected ingredients in dietary supplements designed or claimed to enhance exercise and athletic performance. Manufacturers and sellers promote these products, sometimes referred to as ergogenic aids, by claiming that they improve strength or endurance, increase exercise efficiency, achieve a performance goal more quickly, and increase tolerance for more intense training. These effects are the main focus of this fact sheet. Some people also use ergogenic aids to prepare the body for exercise, reduce the chance of injury during training, and enhance recovery from exercise [1,2].
Dietary supplements to enhance exercise and athletic performance come in a variety of forms, including tablets, capsules, liquids, powders, and bars. Many of these products contain numerous ingredients in varied combinations and amounts. Among the more common ingredients are amino acids, protein, creatine, and caffeine. According to one estimate, retail sales of the category of sports nutrition supplements totaled $5.67 billion in 2016, or 13.8% of $41.16 billion total sales for dietary supplements and related nutrition products for that year [3].
For any individual to physically perform at his or her best, a nutritionally adequate diet and sufficient hydration are critical. The Dietary Guidelines for Americans [10] and MyPlate [11] recommend such an eating plan for everyone. Athletes require adequate daily amounts of calories, fluids, carbohydrates (to maintain blood glucose levels and replace muscle glycogen; typically 1.4 to 4.5 g/lb body weight [3 to 10 g/kg body weight]), protein (0.55 to 0.9 g/lb body weight [1.2 to 2.0 g/kg body weight]), fat (20% to 35% of total calories), and vitamins and minerals [12].
A few dietary supplements might enhance performance only when they add to, but do not substitute for, this dietary foundation. Athletes engaging in endurance activities lasting more than an hour or performed in extreme environments (e.g., hot temperatures or high altitudes) might need to replace lost fluids and electrolytes and consume additional carbohydrates for energy. Even with proper nutritional preparation, the results of taking any dietary supplement(s) for exercise and athletic performance vary by level of training; the nature, intensity, and duration of the activity; and the environmental conditions [13].
Sellers claim that dozens of ingredients in dietary supplements can enhance exercise and athletic performance. Well-trained elite and recreational athletes might use products containing one or more of these ingredients to train harder, improve performance, and achieve a competitive edge. However, the National Athletic Trainers' Association acknowledges in a position statement that because the outcomes of studies of various performance-enhancing substances are often equivocal, using these substances can be controversial and confusing [14].
Most studies to assess the potential value and safety of supplements to enhance exercise and athletic performance include only conditioned athletes. Therefore, it is often not clear whether the supplements discussed in this fact sheet may be of value to recreational exercisers or individuals who engage in athletic activity only occasionally. In addition, much of the research on these supplements involves young adults (more often male than female) and not adolescents who may also use them against the advice of pediatric and high-school professional associations [7,15]. The quality of many studies is limited by their small samples and short durations, use of performance tests that do not simulate real-world conditions or are unreliable or irrelevant, and poor control of confounding variables [12]. Furthermore, the benefits and risks shown for the supplements might not apply to the supplement's use to enhance types of physical performance not assessed in the studies. In most cases, additional research is needed to fully understand the efficacy and safety of particular ingredients.
Many exercise and athletic-performance dietary supplements in the marketplace contain multiple ingredients (especially those marketed for muscle growth and strength). However, much of the research has focused only on single ingredients. One, therefore, cannot know or predict the effects and safety of combinations in these multi-ingredient products unless clinical trials have investigated that particular combination. Furthermore, the amounts of these ingredients vary widely among products. In some cases, the products contain proprietary blends of ingredients listed in order by weight, but labels do not provide the amount of each ingredient in the blend. Manufacturers and sellers of dietary supplements for exercise and athletic performance rarely fund or conduct scientific research on their proprietary products of a caliber that reputable biomedical journals require for publication.
Table 1 briefly summarizes the findings discussed in more detail in this fact sheet on the safety and efficacy of selected ingredients in dietary supplements to enhance exercise and athletic performance. Some research-derived data are available on these ingredients on which to base a judgment about their potential value to aid exercise and athletic performance. These dietary supplement ingredients are listed and discussed in the table, and in the text that follows the table, in alphabetical order.
* References to support statements in Table 1 are provided in subsequent text.
** The evidence of efficacy and safety is for the individual ingredients. The efficacy and safety of these ingredients might be different when they are combined with other ingredients in a product or training plan.
In the text below, each ingredient's section begins with an introduction, followed by a summary of the scientific evidence of that ingredient's efficacy and safety. Each section concludes with information and advice from expert sources, when available, on use of the ingredient as an ergogenic aid.
The preponderance of research to date suggests that exercise-induced reactive oxygen species and nitric oxide are beneficial. These free radicals induce adaptive changes in muscle that lead to greater production of mitochondria and hypertrophy of myofibers [17,21,23,24]. Exposure of cells to high concentrations of various antioxidant supplements (of which vitamins C and/or E have the most evidence) appears to blunt or block cell signaling and thereby inhibit some favorable physiological and physical adaptations to exercise. However, these adaptations might not prevent improvements in VO2max or endurance performance [25].
Among the potential adverse effects of excess vitamin C are diarrhea, nausea, abdominal cramps, and other gastrointestinal disturbances. The intake of excessive amounts of vitamin E increases the risks of hemorrhagic effects. Moreover, results from a large clinical trial show that vitamin E supplements, even at doses below the UL (400 IU/day taken for several years), might increase men's risk of prostate cancer [27]. The side effects of CoQ10 are mild and can include fatigue, insomnia, rashes, nausea, upper abdominal pain, heartburn, sensitivity to light, irritability, dizziness, and headaches [28].
Little research supports the use as ergogenic aids of antioxidant supplements containing greater amounts than those available from a nutritionally adequate diet [19,25]. In fact, they can adversely affect some measures of exercise and athletic performance. The Australian Institute of Sport, part of the government of Australia, does not recommend supplementation with vitamins C and E by athletes, except when they use these products as part of a research protocol or with proper monitoring [29].
Some experts suggest that taking arginine in supplement form enhances exercise and athletic performance in several ways [30-32]. First, some arginine is converted to nitric oxide, a potent vasodilator that can increase blood flow and the delivery of oxygen and nutrients to skeletal muscle. Second, increased vasodilation can speed up the removal of metabolic waste products related to muscle fatigue, such as lactate and ammonia, that the body produces during exercise. Third, arginine serves as a precursor for the synthesis of creatine, which helps supply muscle with energy for short-term, intense activity. Fourth, arginine may increase the secretion of human growth hormone (HGH), which in turn increases insulin-like growth factor-1 (IGF-1) levels, both of which stimulate muscle growth.
Beets are one of the richest food sources of inorganic nitrate. Ingested nitrate might enhance exercise and athletic performance in several ways, primarily through its conversion into nitric oxide in the body. Nitric acid is a potent vasodilator that can increase blood flow and the delivery of oxygen and nutrients to skeletal muscle. Ingested nitrate might also enhance performance by dilating blood vessels in exercising muscle when oxygen levels decline, thereby increasing oxygen and nutrient delivery, reducing the oxygen cost of submaximal exercise, attenuating the adenosine triphosphate (ATP)-creatine phosphate energy system's cost associated with skeletal muscle force production, and improving oxidative phosphorylation in mitochondria [40,41]. Beetroot is available as a juice or juice concentrate and in powdered form; the amount of nitrate can vary considerably among products.
A growing number of clinical trials investigating beetroot juice or concentrate as an ergogenic aid have been published since 2007. Beetroot has generally improved performance and endurance to different extents compared with placebo among runners, swimmers, rowers, and cyclists in time trials and time-to-exhaustion tests, but not in all studies [40,41-45]. Performance benefits are more likely in recreationally active nonathletes than elite athletes [42,46]. One study in 10 recreationally active, young male cyclists suggested a dose-response relationship [47]. Although consuming beetroot juice concentrate on each of 4 days to supply 4.2 mmol nitrate (70 ml) provided no performance benefits compared with placebo, larger amounts of juice supplying 8.4 mmol nitrate (140 ml) did. However, consumption of even more beetroot juice supplying 16.8 mmol nitrate (280 ml) produced no further performance benefits. There has been little study of the effects of beetroot on anaerobic performance, such as high-volume resistance exercise with many repetitions [40].
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