It is estimated that approximately half the U.S. population uses some type of dietary supplement. The International Olympic Committee (IOC) just released a detailed 2018 consensus statement regarding the use of supplements in sport found here:
“Products described as supplements target different issues, including the management of micronutrient deficiencies, supply of convenient forms of energy and macronutrients, and provision of direct benefits to performance or indirect benefits such as supporting intense training regimens.”
Few products have shown strong evidence to directly enhance performance (including caffeine, creatine, specific buffering agents and nitrate). Some other indirect benefits from supplement usage may include “…provision of support for hard training, the manipulation of physique, the alleviation of musculoskeletal pain, rapid recovery from injury, and enhancement of mood.”
What is a supplement?
The US Congress, in framing the 1994 Dietary Supplements Health and Education Act (DSHEA), described a dietary supplement as: “. . . a product, other than tobacco, which is used in conjunction with a healthy diet and contains one or more of the following dietary ingredients: a vitamin, mineral, herb or other botanical, an amino acid, a dietary substance for use by man to supplement the diet by increasing the total daily intake, or a concentrate, metabolite, constituent, extract, or combinations of these ingredients” (Office of Dietary Supplements, National Institutes of Health, 1994).
The problem with this definition is that it is conditional upon having a requisite “healthy diet”. The IOC provides the new definition of:
“A food, food component, nutrient, or nonfood compound that is purposefully ingested in addition to the habitually-consumed diet with the aim of achieving a specific health and/or performance benefit.”
Prevalence of, and Rationale for, Use by Athletes
Surveys suggest that supplement use:
- Varies across different sports and activities
- Increases with level of training/performance
- Increases with age
- Is higher in men than in women
- Is strongly influenced by perceived cultural norms (both sporting and nonsporting)
Motives to use supplements may include:
- To correct or prevent nutrient deficiencies that may impair health or performance
- For convenient provision of energy and nutrients around an exercise session
- To achieve a specific and direct performance benefit in competition
- To gain a performance improvement indirectly accrued from outcomes such as allowing more effective training (i.e., higher intensity, greater volume), better recovery from training sessions, optimizing mass and body composition, or reducing risks of injury and illness
- For financial gain (sponsorship) or because products are provided free of charge
- As a “just in case” insurance policy
- Because they know or believe that other athletes/competitors are using the supplement(s)
Assessing the Evidence Base for Supplement Use
“Performance-enhancing supplements which are claimed to achieve direct or indirect benefits pose a greater challenge in terms of a sound evidence base. With only a few exceptions, there is a scarcity of research, and many of the available studies are not of sufficient quality to warrant their application to elite athletes.”
We can refer to the hierarchy of evidence and further conclude that we need more systematic reviews and meta-analyses. In order for this to occur, we need more well-controlled studies that will be included for review. Ideally, future studies will be randomized, controlled, double-blind scientific trials.
Animal studies provide good information for understanding cellular mechanisms, but may not always be applicable to the athlete and their individual dietary habits. “While the variation in the genome between individuals is less than 0.01%, the variation in microbiota is significant (80–90%), and emerging data suggests that both these factors could affect athletic performance (Clark & Mach, 2017; Ribeiro et al., 2013).” Therefore, we should study humans over animals when possible- without discounting the value of animal-based trials. Also, it would be wise to attempt to strictly control dietary factors over long periods if applicable.
Supplements Used to Prevent or Treat Nutrient Deficiencies
Often times dietary habits address macronutrient ratios but are less considerate of micronutriton. “A frank deficiency of one or more of these nutrients may lead to a measurable impairment of sports performance, either directly or by reducing the athlete’s ability to train effectively (e.g., iron deficiency anemia) or to stay free from illness or injury (e.g., impact of vitamin D deficiency on bone health).” When a suboptimal nutritional status is confirmed, clinicians may prescribe a supplement to help reverse this or at the very least less the effects from deficiencies. See Table 1 for common deficiencies often combatted with supplement usage.
The IOC paper did an excellent job differentiating between supplement that directly and indirectly enhance performance. Below are a series of tables that summarize each.
It is not unknown that excessive consumption of certain ingredients may show adverse effects.”Poor practices by athletes include the indiscriminate mixing and matching of many products without regard to total doses of some ingredients or problematic interactions between ingredients. Even commonly-used products may have negative side effects, especially when used outside the optimal protocol.”
“According to the Dietary Supplements Health and Education Act 1994 (DSHEA) passed by US Congress, nutritional supplements sold in the United States that do not claim to diagnose, prevent, or cure disease are not subject to regulation by the Food and Drug Administration (FDA).” Therefore, the supplement market is effectively unregulated. “This means that there is no requirement to prove claimed benefits, no requirement to show safety with acute or chronic administration, no quality assurance of content, and no liberal labeling requirements.”
For athletes that are being tested under WADA (World Anti-Doping Agencey), a great concern is consuming illegal ingredients unknowingly, that were not identified in a supplement. There has been numerous reports of supplement contamination that has resulted in athlete suspension; even if consumed unknowingly. “It is difficult to gain a perspective of the true prevalence of supplement contamination. Although the original study reported that ∼15% of more than 600 products acquired from around the world contained undeclared prohormones (Geyer et al., 2004), this and other investigations rarely include a truly random sample of the supplements and sports foods used by athletes. Some individual products or categories of products can be considered inherently more at risk of contamination due to the country of origin, the manufacturer, the type of product, and the range of declared ingredients” (found here).
There are no guarantees that any supplement is safe or pure to what it is claimed to be. Currently, independent third party auditing is being done and certain manufacturing countries as being identified as lower- vs higher-risk for false reporting/contamination.
Practical Implications and Decision Tree
When deciding to take a supplement, reliable information should be gathered to further understand the potential health/performance costs and rewards that may ensue. It is best to consult a clinician who works specifically with athletes. It is also important to know that a certain level of trial and error may be necessary to create the ideal protocol for the individual athlete and their unique situation.
Supplements comprise a small, yet noticeable, piece of the puzzle for an athletes nutritional plan. “Some supplements, when used appropriately, may help athletes to meet sports nutrition goals, train hard, and stay healthy and injury free. A few supplements can directly enhance competition performance.” A thorough cost-benefit analysis should be done for each supplement an athlete may consume. It is recommended to consult an experienced clinician during this process.
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