There is no single definition, legal or within the nutritional sciences, of what constitutes a dietary supplement. There are several and they may be unsatisfactory, as it depends on whether or not a “healthy diet” is consumed. There is another definition for supplement: “A food, dietary component, nonfood or nonfood compound that is intentionally ingested in addition to the diet usually consumed, with the purpose of achieving a specified benefit in terms of health and/or performance”. Nutritional supplements are used by athletes at all levels of sport, reflecting the prevalence of their use in society at large. About half of the adult U.S. population uses some form of dietary supplement, and while there are regional, cultural, and economic differences, a similar prevalence is likely in many other countries. Athletes describe a number of different reasons for their supplement choices, and products that fit the “supplement” description may choose different roles within the performance plan.
The specific uses of the supplements reported by athletes take the direct performance enhancement or indirect benefits that come from providing support for training hard, body manipulation, musculoskeletal pain relief, rapid recovery from injuries, and mood boost. With such widespread use of supplements in the general population and with athletes specifically aiming for peak performance, it is not surprising that a high prevalence of supplement use is reported in the majority of surveys of athletes. Survey comparisons are confounded by a number of factors: These include differences in the definition of what constitutes a dietary supplement; inappropriate sample selection; and the use of non-standardized survey tools. However, surveys generally suggest that supplement use varies between different sports and activities and increases with level of training or performance. Furthermore, it increases with age, is higher in men than in women and is strongly influenced by perceived cultural norms (sports and otherwise).
While athletes often consume supplements to take advantage of anticipated/stated effects or benefits, a variety of motivations underlie supplement use. For example, athletes use supplements:
- correct or prevent nutritional deficiencies that may compromise health or performance;
- for the convenient supply of energy and nutrients around a training session;
- to achieve a specific and direct competitive performance advantage;
- to obtain an improvement in performance indirectly resulting from the results, such as enabling more effective and better recovery from training sessions, optimization of body mass and composition or reduction of the risks of injury and disease;
- for profit or because the products are provided free of charge;
- because they know or believe that other athletes/competitors are using supplements.
Many micronutrients play important roles in regulating the processes that support sports performance, ranging from energy production to the production of new cells and proteins. A deficiency in one or more of these nutrients can lead to a measurable deterioration in sports performance – either directly or by reducing the athlete’s ability to train effectively (e.g., iron deficiency anemia) or to remain disease free or injury (e.g. vitamin D deficiency on bone health). Athletes are not immune to poor dietary practices or the increased nutrient loss/need found in some members of the general population, and may also be at greater risk for deficiencies due to increased nutrient turnover or greater losses. Some performance enhancing supplements may, at present, be considered with an adequate level of support to suggest that marginal performance gains may be possible.
These supplements include caffeine, creatine, carnitine, nitrates, bicarbonate, and possibly beta-alanine as well. Performance enhancing supplements should only be considered where a strong evidence base supports their use as safe, legal and effective, and ideally after appropriate sports nutrition dietary practices. Whenever possible, athletes should be thoroughly athlete tested in training that mimics the competition environment as closely as possible before engaging in a competition setting. The disease is a major problem for athletes if it interrupts training or occurs at a critical time, such as during a draft event or major competition. Athletes could benefit from nutritional supplements to support immunity in these scenarios and at other times when they are susceptible to infection (for example, during common cold weather and after long-haul travel) or suffer from an infection. Vitamin C during times of strenuous exertion and zinc at the onset of symptoms may be helpful.
Protein is considered the main ingredient in supplements that promote weight gain, and evidence-based analyzes conclude that protein is effective in promoting lean mass gain when combined with resistance exercise. The evidence of effectiveness for “fat burning” supplements is far from conclusive, however, and there is a complete absence of evidence for the effectiveness of the vast majority of supplements marketed in this category. Adverse effects from supplement use can result from a number of factors, including the safety and composition of the product itself and inappropriate usage patterns by athletes. Inappropriate practices by athletes include the indiscriminate mixing and matching of many products without regard for the total doses of some ingredients or problematic interactions between ingredients. Even commonly used products can have negative side effects, especially when used outside the optimal protocol. For example, iron supplementation in those with already adequate iron stores can cause symptoms that can start with vomiting, diarrhea and abdominal pain.
The “more is better” philosophy, when applied to caffeine, can cause side effects, including nausea, anxiety, rapid heart rate and insomnia, that outweigh the performance benefits. The biggest concern for athletes competing under an anti-doping code (usually the World Anti-Doping Code, published by WADA) is that supplements may contain Prohibited Substances that result in an Anti-Doping Rule Violation (ADRV). It should also be recognized that common supplements, including vitamin C, multivitamins and minerals have also, albeit rarely, been found to contain prohibited substances. In some cases, the amount of the prohibited substance in the supplement may be large, even exceeding the normal therapeutic dose. Most reports of adverse health outcomes from supplement use have focused on liver problems of varying degrees of severity, but other organs are also affected. Professional advice is often important to ensure that the athlete is sufficiently knowledgeable about the appropriate protocol for using these supplements.
But individual athletes can respond very differently to a given supplement, with some showing a markedly beneficial effect while others have no benefit or even a negative effect on performance. Athletes should see good evidence of performance or other benefits, and should be confident that they will not be detrimental to health, before accepting the financial costs and health or performance risks associated with any supplement. Finally, the athlete should be confident, if supplements or sports foods are to be used, that they have undertaken due diligence to procure products with low risk of containing prohibited substances..
- edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
Scientific references
Peeling P et al. Int J Sport Nutr Exerc Metab 2018.
Rawson ES et al. Int J Sport Nutr Exerc Metab 2018.
Peake JM et al. J Appl Physiol 2017; 122:1077–87.
Tipton KD. Sports Med 2015; 45(Suppl 1):93–104.