In some cases, the motives for use and the supplements used show a great deal of incongruence. This suggested a lack of knowledge or understanding of nutritional supplements' effects, except vitamin C, which was associated, but not strongly with preventing illness (i.e. those who take supplements for health reasons tend to take vitamin C). No other supplement pairing with motive for use revealed either a strong or intermediate association.
Athletes' responses were also inconsistent regarding medical advice informing supplement use. This is a worrying sign considering that about 60% of athletes seem to take supplements (Figure ), but many apparently do not do so because of medical advice. This is interesting because when asking about individuals providing information and advice regarding doping issues, medical practitioners appeared to be the most common information source [20
]. Team doctors were the only group that obtained net positive ratings (net positive ratings were calculated in the UK Sport report by subtracting the number of no-selections of doctors from the number of affirmative answers on the same). Yet, no significant association was found between medical advice and any supplements used except iron.
The benefits and drawbacks of supplement use have received considerable attention in recent years, with conflicting reports frequently appearing in the literature. The complex nature of unregulated supplement use seriously hampers the instigation of studies with robust outcomes commensurate with clinical trial approved procedures. Where reports of the observed safe levels (OSL) of individual supplements exist, they are frequently negated by the practice of intake of levels well beyond the OSL. In addition, the intake of multiple supplements is a common practice which manifests in both a higher number of adverse reactions and in those reactions being more severe [10
]. Regarding supplement use in athletes, further parameters under scrutiny include the interaction between medicines and supplements, the source and purity of supplements and the effects of injury or disease [32
Among all the supplements queried in the survey, vitamin C use can be the most accurately predicted from the reasons given for using such supplements and vice versa
. Athletes are likely to take a combination of substances and perhaps in large doses. Potentially adverse effects of long-term use of vitamin C (for example as a pro-oxidant at high levels) have been established along with the beneficial effects [33
]. Reservations therefore apply to even our most commonly used supplements regarding long-term use and appropriate dosages. These reservations concern: 1) an increased health risk to an otherwise healthy population [4
], and 2) the possibility of positive doping tests caused by supplements containing banned substances.
Supplement use is predominant among athletes (62% of the athletes in this sample indicated use). Research shows that athletes are willing to take supplements based on personal recommendation without gathering reliable information about the substance, often obtaining them directly from retailers and internet sites [15
]. Thus, illegal substances (such as those on the World Anti Doping Agency [WADA] Prohibited List or narcotics) and supplements may reach athletes through the same distribution channels [37
]. In order to regulate the European market, the European Union issued the Food Supplements Directive 2002/46/EC, which was implemented in the UK in 2003, effective from August 2005 [39
]. Under the EU Directive, a so-called 'positive list' has been created listing the allowable vitamins, minerals and permitted chemical forms (sources) of these vitamins and minerals that may be used in food supplements and has been widely criticised for its inconsistent inclusion/exclusion criteria and for the costs involved with adding items to the list [40
]. The Food Standards Agency (UK) has successfully rebutted the EU's attempt and, by virtue of the derogation in Article 4.6. of the Directive, which permits the continued use of vitamins and minerals not on the 'positive lists', the UK supplement market will remain semi-regulated at least until 2009 [40
]. Unless strong evidence is found for adverse effects, health warnings are therefore not likely to be placed on nutritional supplements [5
]. The conundrum is how to obtain the strong evidence in the absence of rigorous regulation which severely limits the validity of data collected.
Accurate and adequate information should be provided to athletes via channels they actually use and in a format they are willing to consider (e.g. ATLAS [41
] and ATHENA [42
]). Research conducted in various settings uniformly came to the conclusion that coaches are the most influential persons on athletes' behaviour, being perceived by athletes as knowledgeable and credible information sources [1
]. It is imperative that education in supplement use advice should become a required part of the accreditation process for coaches in much the same way as psychologists are sometimes trained in psychopharmacology to allow prescription of relevant psychoactive medication.
Further research would benefit from using a sample drawn from a wider cross-section of the athlete population and should explore in more depth athletes' beliefs and knowledge about the effectiveness of supplements. It would also be valuable to focus on differences between endurance and non-endurance athletes in this respect with an expanded list of supplements. The reasons for taking supplements should be further investigated in relation to psychological factors such as blocked or unattainable goals and the extent to which supplement use is perceived as a transitional milestone on the road to becoming a serious athlete. The conundrum of supplement using behaviour can be overcome through this fundamental deconvolution approach.