Dietary Supplements for Exercise and Athletic Performance

What is a dietary supplement in fitness?

What is a Dietary Supplement? According to The National Institute of Health, a dietary supplement is a product intended to supplement the diet. They contain one or more dietary ingredients: vitamins, minerals, herbs or other botanicals, amino acids, and other substances or their components.

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].

Several surveys have indicated the extent of dietary supplement use for bodybuilding and to enhance exercise and athletic performance:

• International surveys found that two-thirds of 3,887 adult and adolescent elite track and field athletes participating in world-championship competitions took one or more dietary supplements containing such ingredients as vitamins, minerals, creatine, caffeine, and amino acids [4]. Supplement use increased with age and was significantly more common among women than men.
• A survey of 1,248 students age 16 years or older in five U.S. colleges and universities in 2009–2010 found that 66% reported use of any dietary supplement. The reasons for use included enhanced muscle strength (20% of users), performance enhancement (19% of users), and increased endurance (7% of users) [5]. Products taken for these purposes included protein, amino acids, herbal supplements, caffeine, creatine, and combination products.
• In a national survey of about 21,000 U.S. college athletes, respondents reported taking protein products (41.7%), energy drinks and shots (28.6%), creatine (14.0%), amino acids (12.1%), multivitamins with caffeine (5.7%), beta-hydroxy-beta-methylbutyrate (HMB; 0.2%), dehydroepiandrosterone (DHEA; 0.1%), and an unspecified mix of testosterone boosters (1.6%) [6]. Men were much more likely to take performance-enhancing products than women, except for energy drinks and shots. Among the sports with the highest percentage of users of performance-enhancing products were ice hockey, wrestling, and baseball among the men and volleyball, swimming, and ice hockey among the women.
• In a review of studies on adolescent use of performance-enhancing substances, the American Academy of Pediatrics concluded that protein, creatine, and caffeine were the most commonly used ingredients and that use increased with age [7]. Although athletes used these ingredients more than nonathletes, teenagers not involved in organized athletic activities often took them to enhance their appearance.
• A survey of 106,698 U.S. military personnel in 2007–2008 found that 22.8% of the men and 5.3% of the women reported using bodybuilding supplements, such as creatine and amino acids, and 40.5% of the men and 35.5% of the women reported using energy supplements that might contain caffeine and/or energy-enhancing herbs [8]. Use of these products was positively associated with deployment to combat situations, being younger than 29 years, being physically active, and reporting 5 or fewer hours of sleep a night.

It is difficult to make generalizations about the extent of dietary supplement use by athletes because the studies on this topic are heterogeneous. However, the data suggest that [9]:

• A larger proportion of athletes than the general U.S. population takes dietary supplements.
• Elite athletes (e.g., professional athletes and those who compete on a national or international level) use dietary supplements more often than their nonelite counterparts.
• The supplements used by male and female athletes are similar, except that a larger proportion of women use iron and a larger proportion of men take vitamin E, protein, and creatine.

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.

Selected Ingredients in Dietary Supplements for Exercise and Athletic Performance

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.

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