The aim of this study was to investigate the prevalence of dietary supplement usage in elite athletes from different sports and to provide information about how athletes manage the use of these supplements. We gathered information about the number and type of supplements consumed in the last year, when and why the supplements were consumed, along with data about purchasing routines and certification of supplement quality/safety. The current investigation was shaped by the recent suggestions for improving research on dietary supplement use as raised by Knapik et al. . The investigation relied on a questionnaire that included definitions and examples of dietary supplements. It also contained specific categories of dietary supplements along with open and closed questions for participants to respond to. A wide variety of sports were solicited for questioning. Although a similar aim has been pursued in several previous investigations [12,13,14,15,16], this current study is novel because it expands upon the most common practices employed for the management and administration of dietary supplements in a sample of elite athletes. Finally, the study is innovative because categorizes dietary supplements according to the last consensus of the IOC .
Overall, the use of at least one dietary supplement was reported by 64% of the study sample, a proportion within the range of previous investigations carried out in similar samples in Europe [1, 14]. However, several demographic variables affected the proportion of athletes that consumed dietary supplements in the last year. Sex, age, level of competition, and professionalism influenced this proportion. The sociotype of a typical dietary supplement user is a 36–40-year-old male that competes at a national level, but in a sport that allows professionalism. Interestingly, age was the strongest predictor of dietary supplement use which confirms this variable as an important modulator of the decision to use supplements to obtain performance and/or health benefits, as previously found [13, 29]. The use of dietary supplements by youngest athletes is likely monitored by parents and coaches compared with older athletes who might have more opportunity to engage in unsupervised supplements use .
The sport discipline was another variable with great influence in the proportion of dietary supplements use (Table 1). The sport with the highest proportion of dietary supplement use was bodybuilding, with 95% of body-builders reporting the use of at least one supplement/year. Cycling, athletics triathlon, and aquatics also had high frequencies of dietary supplement use, as observed in elite Portuguese athletes, where the number of training hours –normally higher in endurance-based activities-- was associated with an increased supplement consumption . Additionally, other studies also confirms that endurance athletes appear to consume more supplements than athletes engaged in sprint-based activities . Interestingly, team sports (i.e., football, volleyball, field hockey, etc) presented a non-significant lower proportion of athletes that used supplements. This data coincides with previous publications in samples of Spanish tennis  and basketball players  where individual athletes reported a higher use of supplements than in team sports (81% vs 58%). Even in the sports with the lowest proportion of supplement use (i.e., gymnastics and Basque pelota), one out of two athletes reported the supplement use. This data reinforces the idea that characteristics of the sport influence the general use of dietary supplements in sports while it supports the establishment of dietary supplementation as a common tool for athletes of all types of sport disciplines.
The number of consumed supplements also presented a high interindividual variability with athletes consuming between 1 to 12 dietary supplements, as previously found [1, 16] Although the median of supplement consumption per athlete was 3 supplements per year, a high proportion of athletes consumed more than 8 different supplements and at different times of the season. This results suggest that some athletes might be subject to the adverse interactions of polypharmacy  while also laying out the idea of excessive dietary supplement use amongst some athletes. This is more evident by the high reliance of athletes on themselves as being the main source to obtain accurate information about the effect and efficacy of the supplement while they referred themselves as a the main responsible for the plan of supplementation (Fig. 4). As it has been found, receiving dietary counseling by a qualified professional - instead of relying on self-prescription - results in better-informed choices with respect to the use of nutritional supplements related to performance, recovery, and health . This information points towards the necessity of increasing the knowledge of the benefits and risks of supplementation in the elite athlete population. This result highlights the importance of elite athletes placing more reliance on sport nutritionists and scientists to design their supplementation plans. A more informed athlete population will likely reduce the strong effect of purchasing multiple types of supplements that have been driven by dietary supplement manufacturers.
The most consumed dietary supplements were proteins, amino acids/BCAA, multivitamins, glutamine, and creatine (Fig. 3). A very similar pattern for the type of supplements consumed has been reported in other studies where proteins , multivitamins , and creatine  were found to be the most consumed substances. However, as a novelty of this investigation, the data indicate that the most prevalent group of substances were ones that had little scientific evidence (Fig. 1). This effect was produced by the high number of supplements available in the market that contain minimal evidence of its effectiveness. Although this in the first investigation that suggests this finding, it could be ventured from previous literature due to the gaps in knowledge about effective nutrition and supplementation found in coaches and athletes . This outcome is likely the result of current supplementation practices that imply a poor knowledge about the effect and efficacy of supplements along with reliance on sources with low credibility, at least in this sample of high-performance athletes.
The internet is not only a readily accessible outlet for quick purchases, but also a source of information for the claimed effects of dietary supplements. It is also often reported as a preference site of purchase , as it was found in the present study. Nevertheless, the purchase of supplements in physical stores was listed as the main preference for athletes in this study. This might be justified by a possibly increased safety perception by athletes when buying supplements directly to the vendor when compared to buying online, but research on this topic is scarce and the justification of purchase preference merits further research. Because of their graphical attractiveness and ability to interact/share, athletes often prefer internet and social media as preferred tools for obtaining information and/or educating themselves on nutrition-related topics . Possibly, an excessive amount of information readily available on the internet and a high engagement with social media  with marketing campaigns aimed for sports practitioners, might increase the risk for athletes not relying on other professionals to obtain advice.
Lack of legislation on dietary supplements worldwide, the risk of contamination, and the absence of proper information regarding their use and scientific basis [23, 24] may increase the risk for inadequate and excessive use of dietary supplements or even inadvertent doping.
In the sample of athletes that took at least one supplement, four out of five athletes did not know platforms to check safety/quality of supplements. Most solely relied on the brand name for quality and safety. Despite ample evidence that confirms contamination in commercially available products, athletes still purchased supplements with the assumption of safety . Furthermore, only a relatively small percentage of the athletes not taking dietary supplements reported fearing contamination of the supplement. Together, all these results may indicate that athletes are disturbingly unaware of the contamination risks inherent in dietary supplements. Athlete supplement education is a critical need. This is important to not only reduce the cases of unintended doping , but to also avoid unintentional intakes of substances that could potentially have acute and long term side-effects .
This investigation presents some limitations that should be discussed to improve the results’ applicability. Although we used a validated and reliable questionnaire , the timeframe used to report the use of supplements (i.e., “in the last year”) might have induced some error due to imprecision in the number and type of supplements reported. This might be important for those subjects reporting a high number of supplements. We used open and closed questions and provided examples of each supplement category in an attempt to reduce recall inaccuracies. Additionally, although it was made clear that the questionnaire was anonymous, it is possible that due to personal bias, some athletes may have intentionally avoided reporting some information regarding supplement consumption. Finally, some athletes showed some difficulty describing the type of supplement they were taking. To avoid wrongfully identifying supplements, an open space was provided in the questionnaire to fully describe the supplement (name, brand, type, and any other extra information that they could recall) to improve the identification of each supplement. Despite these limitations, the authors believe that the article presents valuable information for the scientific community about patterns of dietary supplementation consumption.