Are dietary supplement users more likely to dope than non-users? a systematic review and meta-analysis

In the past decade, a body of evidence has reported that dietary supplement use is related to prohibited performance enhancing substance use (i.e., doping). To help international and national sport organisations understand the degree to which dietary supplement use is related to doping, the objectives of this systematic review and meta-analysis were to 1) compare the prevalence of doping between dietary supplement users and non-users and 2) identify whether supplement use is related to doping social cognitive factors. We searched for studies sampling athletes and that measured both dietary supplement use and doping in EMBASE, MEDLINE, PsychINFO, CINAHL and SPORTDiscus from database creation to May 2022. Risk of bias was assessed using JBI Critical Appraisal Checklist for cross-sectional studies and the STROBE checklist. Twenty-six cross-sectional studies, involving 13,296 athletes were included. Random-effect models revealed that doping was 2.74 (95% CI=2.10 to 3.57) times more prevalent in dietary supplement users (pooled prevalence = 14.7%) than non-users (6.7%), and that users reported stronger doping intentions (r=0.26, 0.18 to 0.34) and attitudes (r=0.21, 0.13 to 0.28) compared to non-users. Preliminary evidence also suggests that dietary supplement users were less likely to dope if they were more task oriented and had a stronger sense of morality. Results of the review are limited by the cross-sectional design used in all studies and lack of consistency in measurement of dietary supplement use and doping. Data indicate that athletes using dietary supplements are more likely to self-report doping Anti-doping policy should, therefore, target dietary supplement use in anti-doping education programmes by providing alternative strategies for performance enhancement or highlighting the safest ways they can be consumed. Similarly, as a large proportion of athletes use dietary supplements without doping, further research is needed to understand the factors that protect a dietary supplement user from doping. No funding was received for the review. A study protocol can be found here: https://osf.io/xvcaq.