Dietary supplements come in various forms, making it difficult to condense this diversity into a single definition. As there is no definition that is completely satisfactory or context-independent, a proposal was made by the International Olympic Committee (IOC) to encompass this terminology. Thus, dietary supplements were defined as “a food, food component, nutrient or non-food component that is purposefully ingested in addition to the customary diet with the aim of achieving a specific health or performance benefit”.

Athletes are often given many reasons why to take such supplements. Claims such as “to gain muscle”, “to burn fat”, “to boost energy” and “to be healthy” appeal directly to the emotions of athletes pursuing these goals. However, it is important to note that the industry is financially driven and responds to consumer demand and acceptance. In general, the scientific literature favours studies reporting positive findings, as these are most newsworthy. However, some authors warn that only studies showing positive effects are promoted, while those showing negative effects are silenced by sponsors.

BENEFITS OF SUPPLEMENTS IN ELITE ATHLETES

The consensus statement issued by UEFA¹ on nutrition in elite football warns that the nutritional programme for elite athletes should be based on a food-first approach, with supplements playing a residual role for very specific purposes. The dose and duration of such supplementation should be recorded, and responses, both positive and negative, should be monitored by the nutrition team. It is essential that athletes receive regular check-ups.
The proposed classification outlined in the study divides dietary supplements relevant to football players into three main groups: micronutrients, sports nutrition and performance.

MICRONUTRIENTS

Some football players may require supplementation to address their micronutrient deficiency, with vitamin D, calcium and iron deficiencies being the most common concerns. Supplements used for this purpose should be procured from a reliable supplier and used only in a therapeutic dose. Treatment should last just long enough to restore the nutritional deficiency, as an inappropriate dosage could pose a risk to the athlete’s health.

SPORTS NUTRITION

Due to the organisation of training sessions throughout the day, football players sometimes find it difficult to take in food in the form of meals. In this scenario, sports foods such as electrolyte drinks with carbohydrates, energy bars or recovery shakes are a good alternative to achieve nutritional goals.

PERFORMANCE

While it is true that some dietary supplements can effectively enhance performance in a specific exercise or sport, the evidence available that professional footballers benefit from their effects is very limited. Furthermore, the benefits in the realm of football have been shown to be relatively minor in comparison to other sports. Some of these supplements, such as caffeine or creatine, do have a direct impact on performance, but the side effects of inappropriate dosage can be severe – causing anxiety, insomnia or tachycardia in the case of caffeine; and even false increase in creatinine levels that can lead to kidney problems in the case of creatine.

ADVERSE ANALYTICAL FINDINGS IN SUPPLEMENTS

The risk of testing positive in a doping test for the use of dietary supplements has been well documented over the past two decades. Evidence of this can be found in the study by Geyer et al.², which analysed 634 nutritional supplements from 215 suppliers and found that approximately 15% contained undeclared prohormones. In 2007, approximately 25% of 58 types of supplements purchased on the US market were reported to be contaminated with steroids. In a recent study, Matthews³ suggests that “dietary supplements continue to exhibit poor manufacturing processes and intentional contamination with banned substances.”

Historically, anabolic steroids have been the most commonly found drug in muscle growth supplements, while stimulants and anorectic agents are found in tonics and weight loss supplements respectively. In addition, the supplement market has seen a myriad of new products in recent years, containing a wide variety of banned doping substances. Banned stimulants have been found in workout or pre-workout enhancers, while some muscle growth products have featured banned selective androgen receptor modulators.

The presence of these substances, according to the UEFA consensus statement, could be interpreted to reinforce the idea that contamination of supplements is not accidental, but the result of deliberate product adulteration. While it is true that athletes do not deliberately intake these prohibited substances, the principle of liability specifies that ignorance of the presence of these substances does not exempt them from liability and they will still be sanctioned.

It is impossible to completely eradicate the risks arising from the use of dietary supplements, but it is certainly possible to reduce them. The use of third-party testing programmes, such as the Kölner Liste in Germany or Informed Sport in the UK, helps athletes to limit the use of supplements and to choose those which have been assessed by a reputable, independent company to be free of doping agents.

¹ Collins J, Maughan RJ, Gleeson M, et al (2020). UEFA expert group statement on nutrition in elite football. Current evidence to inform practical recommendations and guide future research. doi:10.1136/ bjsports-2019-101961
² Geyer H, Parr MK, Mareck U, et al. Analysis of non-hormonal nutritional supplements for anabolic androgenic steroids – results of an international study. Int J Sports Med 2004;25:124–9.
³ Mathews NM. Prohibited contaminants in dietary supplements. Sports Health 2018;10:19–30.