Improving health literacy on nutritional supplement use in sport: the IRIS European toolkit

Background

Nutritional supplement use is widespread among athletes despite concerns regarding contamination, misleading marketing, adverse effects, and inadvertent doping. Approximately 14% of positive doping tests are linked to contaminated supplements. Limited health literacy may impair athletes’ ability to appraise supplement information and make informed decisions. The IRIS project examined supplement-related knowledge, attitudes, and risk perceptions across Europe to inform an educational intervention.

Methods

A mixed-methods study was conducted across six European countries. Surveys were completed by 468 athletes aged 18–60 years assessing supplement use, knowledge, contamination awareness, and risk perceptions. Semi-structured interviews were conducted with 49 competitive athletes. Additionally, 187 supplement product webpages were analysed for marketing and labelling practices.

Results

Supplement use exceeded 50% in most countries and 60% in Finland and Portugal. Although 62% recognised contamination risks, only 28% consistently verified supplement quality and 12% identified regulatory authorities. Exposure to misleading marketing was reported by 73% of participants, while 41% of analysed products used performance-enhancing drug-associated terminology. Supplement users are 3.5 times more likely to engage in doping-related behaviours. Qualitative findings identified misconceptions regarding efficacy, reliance on informal advice, and social influences on decision-making. These findings informed development of the IRIS Informed Toolkit, a four-module resource addressing supplement literacy, beliefs, risk management, and social influences.

Conclusions

The IRIS Informed Toolkit is an evidence-based health literacy intervention addressing a public health challenge in sport. By strengthening informed decision-making regarding supplement use, it may reduce preventable harms and inform future policy.

Key messages

• Health literacy gaps leave many athletes vulnerable to misinformation, contamination risks, and preventable harms related to nutritional supplement use.

• The IRIS Informed Toolkit translates European multi-country evidence into an innovative educational intervention to support safer supplement use and future policy action.