There were several important findings in this study. First, the DSU was lower in older and more successful players. In addition, both self-perceived and objectively evaluated KN&DS were related to DSU, and therefore, the initial study hypothesis was accepted. However, the S/KN&DS was a stronger predictor of DSU than the O/KN&DS, while the correlations between KN&DS and DSU were more evident in athletes who played team sports with a higher prevalence of DSU.
Previous studies correlated DSU with athletes’ age, but the results were not consistent. For example, our finding of a higher prevalence of DSU in younger and less successful athletes is in agreement with the results of previous related studies performed on sailing athletes and rugby players from the territory of Southeastern Europe [12, 26]. On the other hand, it is in certain disagreement with the findings summarized in the meta-analysis of Knapik et al. where the authors concluded that DS is more prevalent in older athletes [14]. However, the differences may be at least partially explained by the fact that practically all studies, including this one, where higher prevalence of DS is reported for “younger” athletes actually observed adults (+ 18 years) [12, 26], and therefore, we are not speaking about youth-athletes but rather “younger adults”. On the other hand, studies summarized in a previously cited review in which a higher prevalence of DS was evidenced in older athletes mostly compared “youth” with “adult” athletes [14].
Several factors influenced the increase of DSU in modern sports. Most likely, the DSU has become more prevalent because of (i) an increase in the psycho-physiological demands of sports training and competition and because of (ii) supplement market growth and aggressive advertising [14, 27]. Such aggressive marketing is especially oriented toward athletes who seek every legal edge to improve their performance [14, 28]. As a result, there is a certain possibility that younger players are under the stronger influence of both factors (e.g., increased physical demands and aggressive DS advertising). On the other hand, we may not ignore the fact that younger athletes (i.e., less experienced athletes) are probably less skilled than their more experienced (i.e., older) colleagues. As a result, younger athletes lean more toward DSU simply because of their intention to “bridge the gap” between their current abilities (performance) and desired achievement.
The previous discussion is supported by the established correlation between sport achievement and DSU, where more successful players were identified as being less oriented toward DSU. This outcome is in agreement with previous studies where higher DSU was evidenced in athletes who reported lower competitive success [26]. It is almost certain that the higher prevalence of DSU in less successful players is a direct consequence of their (relative) inferiority in sport achievements. Supportively, studies have already confirmed that athletes who are not satisfied with their achieved competitive results will try to improve their capacities by using different techniques [12]. While one of the central motives of DSU in sport is its direct or indirect influence on sport performance, the negative correlation between DSU and achieved-sport result is actually logical [16, 29]. Therefore, proper knowledge about DSs is essential, highlighting the central problem identified in this study (e.g., identifying the association between KN&DS and DSU) as particularly important.
Although the practice of DSU is actually ancient (i.e., historical evidence notes usage even in ancient Olympians), the physiological and psychological demands of sport participation have increased exponentially over the last few decades, coinciding with increased DSU in athletes [17, 28, 30]. Additionally, modern athletes are often in out-of-home situations, travel frequently, consume nonfamiliar foods, train and compete in different climates, etc. These habits disturb usual and convenient food consumption and alter appropriate nutrient intake, which frequently results in DSU [26]. Therefore, proper knowledge of the possible ergogenic effects of DSs, the importance of DSs in the recovery process, and the potential side effects of DSs are crucial for the proper and safe usage of DSs in athletes [20, 31,32,33]. Consequently, the positive correlation between O/KN&DS and DSU established here is encouraging.
On the other hand, it is clear that some athletes who consume DSs overrate their knowledge on nutrition and DS, which is evidenced by the low correlation between O/KN&DS and S/KN&DS (r: 0.10). Almost certainly, the lack of objective knowledge puts those athletes who non-objectively perceive their knowledge on DS as high in danger of inappropriate usage of DS and possible detrimental consequences [25, 34]. Therefore, special efforts are needed to increase the level of knowledge on DS in athletes who are not objective about their expertise on the problem. The importance of systematic and organized education is clearly supported by the fact that the majority of athletes declared “self-education” as the main source of information about nutrition and DS (Fig. 2). Although self-education may be a potentially valuable type of life-long learning, it should not be a main source of information on nutrition and DS issues. Namely, only properly educated athletes will be able to objectively evaluate information obtained from different informal sources (i.e., internet, magazines, food stores) and consequently will be less vulnerable to potential misinformation [35].
The previous discussion is even more important because individuals who overestimate their own KN&DS will likely not improve their knowledge on these topics in the future because of the specific cognitive mechanism known as the “anchoring effect” [36]. In short, the “anchoring effect” is a type of cognitive bias that causes individuals to focus on the first available piece of information (the “anchor”) given to them when making decisions. In this case, athletes with high self-perceived knowledge will be “anchored” by their self-rated knowledge on a topic (i.e., S/KN&DS).
Interestingly, sociopsychological studies have clearly noted that the anchoring effect is moderated by the level of “true knowledge on a problem”, and advanced knowledge decreases the anchoring effect [37]. As a result, we may expect that athletes with high O/KN&DS scores will self-decide to improve their knowledge and awareness of nutrition and DS in the future. On the other hand, athletes with low O/KN&DS scores and high S/KN&DS scores will likely not feel an urgency to improve their knowledge of nutrition and DS through self-education. It is more likely that their knowledge should be transcended through systematical and mandatory educational programs organized by responsible institutions (i.e., sport teams, national/regional sporting federations, and public-health authorities).
Our results indicated sport-specific associations between the studied variables, with stronger correlations between predictors and DSU in sports with a higher prevalence of DSU in athletes. This finding emphasizes the necessity of sport-specific investigation of DSU and of similar topics. Namely, when investigating correlations between certain behaviors and practices in sports (i.e., prevalence of DS, doping-related behaviors, counselling practice), some studies have analyzed athletes involved in different sports and sport disciplines as a homogenous sample of participants [14, 38, 39]. Moreover, different sports often vary in the investigated factors, including predictors (i.e., sociodemographic, sport-specific factors, and knowledge) and criteria (i.e., variables of behavior and/or practice) [40, 41]. Therefore, analyzing athletes involved in different sports as a homogenous sample without acknowledging sport specifics will probably lead to confounding effects in the studied factors. Such effects will consequentially limit the applicability of an analysis in real-sport settings.
The previously discussed findings on the specific associations between subjective and objective evaluation of KN&DS are novel to some extent and therefore make possible the discussion of one specific topic that is not directly related to the aim of the study. The studies that have been conducted so far have reported a positive correlation between DSU and potential and/or current doping behavior in athletes [42, 43]. Consequently, athletes who consume DSs are often targeted as being “vulnerable to doping”. Controversially, in other studies, knowledge on nutrition and DSs was found to be protective against doping behavior [20], while here, we found a correlation between KN&DS and DSU. Overall, we may determine a certain possibility of higher doping likelihood, specifically in athletes who use DSs but subjectively judge their KN&DS as high. This determination could reconcile the different findings of reports in which a higher susceptibility to doping was observed in DS users and opposed reports (with lower susceptibility to doping in DS users) [20, 42, 43]. The importance of these issues makes systematic investigations on this topic warranted.
Limitations and strengths
This study included only athletes involved in team sports from one specific region (e.g., Southeastern Europe) during the competitive season. Additionally, we identified sport-specific associations among the studied factors. Therefore, the results are generalizable to similar samples of athletes in similar circumstances. The cross-sectional design is another important limitation of the study because it does not allow interpretation of cause-effect relationships between variables. Further, in this study power-bars and isotonic drinks are observed as dietary supplements, the list of DSs observed in this study was limited to those most frequently used in the region which may partially skew the results. Therefore, future studies should additionally focus on DS types not observed herein.
This is one of the first studies that systematically studied and objectively compared evaluated and self-perceived knowledge on nutrition and DSs and their potential correlations with DSU in athletes involved in four Olympic team sports. Additionally, important strengths of this investigation included a relatively large sample of participants with a high competitive level from a specific sociocultural environment (i.e., in a region in which the studied sports are the most popular types of sports, a sport-specific design, and the use of previously validated measurement tools.
