The current study highlights the links between dietary supplement consumption and motivation for supplement use among young, Canadian athletes. These results are significant as they provide an, albeit indirect, assessment of the athletes’ knowledge of the benefits – real or purported – of dietary supplements as they relate to health and performance. Research in this demographic is particularly important, as the group consisted mostly of young, club level athletes who were less likely to have access to sport nutrition professional advisors, yet represent the majority of young athletes. Indeed, fewer than half had ever met with a dietitian and 38 % had previously attended a session on dietary or sport supplements . Furthermore, the high prevalence of dietary supplement use suggests that research in this area is essential to ensure safe and effective supplementation practices.
Athlete self-evaluated perceived knowledge of the reasons for supplement use is generally low, although it does increase with age, whereby 60 % of athletes claim to know the reasons for all of the supplements they are consuming by ages 19–25. Indeed this purported level of knowledge is improved as compared to a 2003 study that found 10 % of Singaporean athletes, 85 % of which were 25 years or younger, self-rated their level of perceived knowledge regarding dietary supplements as good or excellent .
Vitamin and mineral supplements were associated with health-related reasons; however, evidence indicates these supplements are only effective in the case of a deficiency  suggesting a lack of congruency; with possible exceptions being vitamin D and calcium (females), which are reportedly low in athletes [11, 12]. In the case of micronutrient deficiencies, dietary changes rather than supplementation should be the primary target to bring intakes into the healthy range. The consumption of sport bars, protein powders, and amino acid supplements was linked to reasons for choosing supplements associated with improved health, particularly immune system enhancement and to improve diet quality. In cases of inadequate dietary intake of protein, performance foods high in protein (protein bars, recovery drinks, protein powders, etc.) would be beneficial, suggesting congruence between the actions and motivation; however, when dietitians observed nutritional habits in young athletes, they found protein intakes to be more than sufficient. Average protein intake in male athletes was 2.3 g/kg body weight, which is significantly higher than the recommended upper intake for athletes of 1.7 g/kg body weight, and 86 % of females met the recommended intake with an average intake of 1.4 g/kg body weight . Furthermore, in Canadian, high-performance athletes, protein intakes were 1.7 g/kg body weight from food alone and 1.8 g/kg body weight from food and supplements in females and 1.9 g/kg body weight from food alone and 2.1 g/kg body weight from food and supplements for males , clearly indicating protein is not a nutrient of concern for most athletes.
Evidence of congruence between health-related reasons for supplementation and actual practice also exists in that creatine, energy drinks, sport gels and gummies, and sport drinks were rarely associated with health reasons; indicating athletes are potentially able to distinguish between supplementation for health and performance in these cases. Conversely, it has been suggested that consuming a 6 % or greater carbohydrate beverage, such as a commercial sport drink, during prolonged exercise can reduce the risk of upper respiratory tract infections, potentially creating the case for sport drinks and improved immune function . Fatty acid consumption was associated with health-related reasons and although omega-3 fatty acids are believed to have anti-inflammatory properties, there is currently insufficient evidence to determine if they are capable of altering immune function in athletes . Plant extracts encompass a large group of dietary supplements, however, echinacea and ginseng are consistently popular  and these examples were provided in our questionnaire. With respect to motivation for supplementation with plant extracts, health-related reasons such as “prevent or heal illnesses or injuries”, “support immune system” and “strengthen overall health”  have been reported, which is in agreement with our participants. Unfortunately, there is a paucity of high-quality, human studies to evaluate the effects of herbal supplements on health-related reasons for supplementation in athletes and as such, the potential benefits cannot be confirmed . While the effectiveness of most plant-based natural health products remains to be determined, one should acknowledge these products are generally marketed for health reasons.
The use of dietary supplements to enhance performance in young athletes is controversial. Some experts recommend that athletes under the age of 18 years avoid using dietary supplements unless required for a medical reason and only in cases where they are supervised by a professional . Although this advice is sound in that it errs on the side of safety, it is perhaps not realistic and certainly the high rates of dietary supplement use suggest athletes are not heeding this conservative message. Regardless, if an athlete opts to take supplements, the chosen dietary supplements should be found to be effective in relation to their performance goals.
A large percentage of athletes consumed vitamin or mineral supplements and there was an association with motivation for enhanced performance; however, as with health-related reasons, the conventional thinking is that vitamin and mineral supplements will not improve performance, except in the case of a deficiency, illness or restricted food intake . Vitamin-enriched waters were also associated with performance reasons, however, are unlikely to benefit athletes if dietary intakes are adequate and concerns have been raised regarding the added sugars in some vitamin-enriched water options. Protein powders and various amino acid products were commonly reported in athletes looking to improve performance, a finding supported by others [7, 18]. These products are frequently advertised to increase muscle mass and performance , indicating some level of congruence between the performance goals and supplement choice. Protein supplementation has been found to improve muscle hypertrophy and strength, as well as aerobic and anaerobic power, when combined with appropriate training , conversely, less support exists for potential benefits with recovery of muscle function, muscle soreness, and muscle damage .
Energy drink consumption was also positively associated with performance reasons, notably “increase energy” and “muscle mass/strength” in these athletes. Energy drinks may improve neuromuscular performance, delay central nervous system fatigue, and increase endurance performance [21, 22], however, the optimal dose and their potential superiority to a sport drink is unclear. Furthermore, there are concerns with energy drinks as a hydration choice, in those who are not habituated, as they may increase water and sodium losses and have a mild thermogenic effect . Other potential side effects include: increased sugar intakes, gastrointestinal problems, tachycardia, anxiety, headaches and insomnia [21, 22]. In general, energy drinks are contraindicated for those under the age of 18 years and their consumption should be discouraged except in very specific circumstances and under parental guidance [22–24]. Creatine supplementation was associated with “muscle mass/strength”, “endurance”, and “overall athletic performance”; indeed there is evidence to suggest creatine may be efficacious in enhancing muscle hypertrophy and performance in short, high-intensity activities, however, the majority of the research has been conducted in adult males . Younger athletes could benefit from creatine supplementation, as their ability to regenerate high energy phosphates is reduced; nonetheless, the International Society of Sports Nutrition only deems creatine supplementation acceptable if the athlete is past puberty, competing at a high level, has parental approval, is supervised by a qualified professional, and uses an appropriate dose [25, 26].
Consuming carbohydrates or carbohydrate-electrolyte combinations during exercise can delay fatigue, thereby improving performance in intermittent and prolonged endurance exercise [27, 28]. Arguably, congruence exists between the use of sport/electrolyte drinks and sport gummies/gels and performance-based motivations for supplement use. Carbohydrate intake during exercise has been identified as an area where young athletes do not meet the recommendation of 30–60 g/h, in at least one study , suggesting that this link could be highlighted in sport nutrition education. The use of these products should be carefully considered in the context of the duration and intensity of the exercise, however, as there is a concern with the use of sport drinks and excess calories in the form of added sugars . Plant extracts were also associated with performance reasons, yet controversy exists regarding the potential benefits of common plant extracts such as echinacea [16, 29, 30] and ginseng  on athletic performance.
Vitamin and mineral supplements, fatty acids, energy drinks, sport/protein bars, and gels and gummies were associated with “because someone told you to” or “because family/friends/teammates do”. These results are in-line with a study in young, elite German athletes that found coaches (37 %), family (30 %), physicians (29 %), and nutritionists (14 %) provided information on dietary supplements. Furthermore, 16 % of athletes learned about dietary supplements from the media and 27 % reported that they did not receive any information about dietary supplements from anyone . As may be expected, the younger the athlete, the more likely they are to consume supplements because others have told them to. Certainly, encouraging young athletes to heed the advice of others, particularly their parents or guardians, is advisable; however, the sport nutrition knowledge of these individuals is uncertain. Influence of others on dietary supplement use, particularly those who may not possess the appropriate knowledge, is a common cause for concern in athlete populations [33, 34]. Clearly education is required not only for the athletes but also their support network, as there is obviously a willingness to try supplements based on the recommendations of others rather than personal knowledge.
Our study is limited in that young participants completed the questionnaire using personal recall and there may be errors due to a lack of understanding. Delivering the questionnaire in a “face-to-face” mode, where they could ask questions and receive explanations minimized this limitation. Additionally, the athletes were not specifically asked the reason for consuming each supplement; rather, the analysis looks at associations within the data, therefore, the magnitude of the association was reported and should be considered in the interpretation of the results. Future research that directly measures athlete knowledge regarding dietary supplements and relates this knowledge to their motivation for supplementation and actual intakes would be valuable to gain a more in-depth understanding.