To our knowledge, this study is the first to investigate the prevalence of NS use and differences in NS use by gender, age, and discipline among elite Japanese TF athletes. As the principal result, we found that 63.9% of elite Japanese TF athletes took some kind of NS. While only a few studies have reported the prevalence of NS use in TF athletes, the present result is consistent with the previous finding that the prevalence of NS use in top-level TF athletes was 66.8%, according to an analysis of doping control forms collected during 12 World Athletics (WA) World Championships and 1 out-of-competition season . Tscholl et al. reported that the prevalence of NS use among elite football players in the Fédération Internationale de Football Association (FIFA) World Cup was 57.1%, which was lower than that found in TF athletes . Several studies have also found that TF athletes tended to report a high prevalence of NS use compared with athletes involved in other sports [8, 11]. Physique and morphological characteristics play important roles in competition success among TF athletes . The relatively high prevalence of NS use among TF athletes might therefore be reasonable.
While Asian TF athletes were reported to consume fewer NS (mean number of products per athletes: 1.1) than athletes from other continents, except for Africa (1.9, 1.9, 2.2, and 2.0 for Europe, North America, Oceania, and South America, respectively), that study included many developing countries in Asia, and a country-by-country analysis was not conducted . The mean number of NS products used per athlete in the present study was 1.4. The JISS reported that the mean number of NS products used per TF athlete who participated in the 2012 London Olympic Games was 1.7 . These findings clearly show that Japanese elite athletes tend to use NS much more frequently than those of other Asian countries.
The present study also revealed that the prevalence of NS use differed by gender and age. More women (69.2%) reported the use of NS than men (59.6%), as was also noted in the previous report from the IAAF . Further, gender differences were also seen in the prevalence of components. Women showed a higher prevalence than men of using vitamins or minerals, while men showed a higher prevalence than women of using protein, creatine, and caffeine.
According to the analysis by age category, senior athletes showed a higher prevalence of all NS components (except for carbohydrates) (68.9%) than junior athletes (58.9%), indicating that the prevalence of NS use increased with increasing competitive level. This finding was further supported by the higher prevalence of NS use (86.2%) among Japanese TF Olympic athletes at the highest competition level  than among athletes in the present study. However, the prevalence of NS use among Japanese junior TF athletes (58.9%) was nearly 3 times that among general Japanese high school students . Neiper et al. also reported that the prevalence of NS use was 62% among elite junior TF athletes in the UK, with a trend toward more frequent use by women (75%) than men (55%) . These findings suggest that NS use is widespread among not only senior athletes but junior athletes as well, although safety data concerning the use of NS by young populations are largely lacking [27, 28].
While a previous study showed a lower prevalence of NS use among middle- and long-distance athletes than those who participate in power events, such as sprinting, throwing, and jumping , we obtained the opposite result in the present study, with the prevalence of NS use being significantly higher among long-distance athletes than those who participated in other disciplines. Indeed, three-quarters of long-distance runners evaluated in the present study were taking some kind of NS. In particular, the rate of mineral use was two to five times higher among long-distance runners than those participating in other disciplines. The high prevalence of iron deficiency anemia in Japanese endurance athletes might be contributing to the frequent use of NS containing minerals, including iron, by long-distance runners. The JAAF medical committee surprisingly reported that the self-assessed incidence rate of anemia among middle- and long-distance runners at elite Japanese high schools was relatively high, at 31.5% in boys and 46.1% in girls . Tscholl et al. similarly reported the frequent use of iron supplements among middle- and long-distance runners .
Almost half of the elite Japanese TF athletes in this study reported the use of amino acids and vitamins, which were the most prevalent components in the present study. This result was attributed to the frequent use of a specific product containing branched-chain amino acids (BCAAs; leucine, isoleucine, and valine) and multivitamins that is popular among Japanese athletes and has been actively promoted to them. The JISS also reported that amino acids were the most commonly used agent among Japanese elite athletes [11, 30]. However, only limited evidence exists to support the hypothesis that BCAA supplementation during intense training helps minimize protein degradation and thus leads to greater gains in fat-free mass [15, 31,32,33]. In the ISSN exercise & sports nutrition review, essential amino acids (EAAs) are categorized as supplements with strong evidence supporting their efficacy and are apparently safe only for muscle building; however, BCAAs are categorized as supplements with limited or mixed evidence supporting their efficacy for muscle building and performance enhancement . Of note, the effect of BCAA supplementation in stimulating an increase in muscle protein synthesis was notably weaker than that of full component EAA . Moreover, several studies have reported that BCAA supplementation was ineffective for improving performance and reducing skeletal muscle damage in endurance events [34, 35]. Considering the limited evidence supporting the efficacy of amino acids in endurance events, the finding that Japanese elite long-distance runners tend to consume NS containing amino acids warrants further investigation.
Although vitamin and mineral supplementation is not necessary for athletes with an adequate diet [12,13,14], such supplementation might be warranted for female athletes at risk of vitamin or mineral insufficiency due to inadequate dietary intake, menstruation, or inflammatory responses to heavy physical activity . Indeed, the women in the present study tended to show a higher prevalence of vitamin and mineral consumption than men. However, further studies should clarify whether such supplementations are necessary with consideration to dietary intake, nutritional status, and exercise volume.
Among the ergogenic aids included in NS in the present study, creatine and caffeine have been classified as supplements with strong evidence supporting their efficacy in enhancing sports performance [3, 15]. Studies have consistently shown that creatine monohydrate supplementation increases intramuscular creatine concentrations, which may help explain the observed improvements in high-intensity exercise performance, thus leading to greater training performance . The most effective way to increase muscle creatine stores is to ingest 5 g of creatine monohydrate (or approximately 0.3 g/kg body mass) 4 times daily for 5–7 days, followed by 3–5 g/day thereafter in order to maintain elevated creatine levels [3, 15, 37]. Creatine supplementation with long-term use appears to have no negative health effects in healthy individuals when appropriate loading protocols are followed [38, 39]; however, a potential small increase in body mass after creatine loading as a result of water retention may be detrimental for sports with weight classes/restrictions or where an increased body mass may decrease performance, such as in long-distance and jumping events [3, 40]. The WA Consensus Statement 2019 (Nutrition for Athletics) noted that creatine supplementation may help achieve a marginal performance gain in all TF disciplines except for middle- (1500 m) and long-distance events [41, 42]. This notion is consistent with the results of the present study, where approximately one-quarter of sprinters and throwers but no middle-distance runners and only a few long-distance runners reported the use of creatine.
Caffeine has also been shown to be an effective ergogenic aid that possesses well-established benefits for athletic performance across endurance-based situations and short-term, supramaximal, and/or repeated sprint tasks when 3–6 mg/kg of body mass is consumed within 60 min before and/or during exercise in the form of anhydrous caffeine (i.e. pill or powder form) [3, 15, 43,44,45,46]. The IAAF also regards caffeine as an effective ergogenic aid for performance enhancement in all TF disciplines [41, 42]. A review and meta-analysis showed that the consumption of caffeine-containing energy drinks improved performance in several physical and sport situations that included muscle strength protocols, jumping, endurance exercise tests, and sports-specific actions . Another review reported that caffeinated coffee may also be used as a safe alternative to anhydrous caffeine to improve endurance performance . Although the prevalence of caffeine-containing NS use was lowest, at only 1.2% in the present study, despite strong evidence of positive impact on sports performance, prevalence might have been higher if consuming caffeine-containing beverages, such as energy drinks, coffee, or tea, had been counted as caffeine supplementation. However, increased caffeine doses should be avoided, as caffeine doses over ≥9 mg/kg body mass do not appear to increase the performance benefit and are instead likely to increase the risk of negative side effects, including nausea, anxiety, insomnia, and restlessness [3, 48, 49].
The WA also listed nitrate/beetroot juice, beta-alanine, and sodium bicarbonate as well as creatine and caffeine as performance supplements that may help improve performance in TF events [41, 42]; however, no athletes in the present study reported the use of such supplements, given that nitrate, beta-alanine, and sodium bicarbonate are relatively unfamiliar to Japanese populations. Considering the gap between the prevalence of use of a given NS and the evidence supporting its efficacy, athletes may very well consume NS without closely evaluating their efficacy on improving performance in events or safety.
While we did not evaluate the reasons for the use of NS, Garthe and Maughan et al. reported that some athletes consumed NS not only for performance and/or health benefits but also for other reasons, such as a “just in case” insurance policy, financial gain (sponsorship), or on advice from other parties, including coaches, fellow athletes, parents, and marketing . A marked influence of coaches, managers, and trainers on supplementation practices was also reported in a previous study targeting Japanese Olympians . In addition, a lack of knowledge concerning active ingredients, mechanisms of action, recommended doses, and adverse effects of NS has been reported among athletes [20, 50]. Surprisingly, Braun et al. found that only 36% of elite young German athletes were aware of the issue of supplement contamination . To prevent adverse effects or unintended ARDVs due to using contaminated NS, athletes must be alerted to these risks and advised to take precautions against the blind consumption of NS on the advice of individuals other than themselves, or the unnecessary use of NS without evidence.
One limitation associated with the present study was our method of evaluating NS use. The prevalence of NS use was assessed based on response to the PMF by the athletes themselves, and no objective methods were practiced. Further, differences among individuals in the definitions of NS might have led to underestimation of the prevalence of NS use. Variations in the number of subjects by discipline may also have been a limitation. Finally, since we assessed the use of NS only before athletes participated in competitions, our results might not accurately reflect their daily usage throughout the calendar year.