Are Dietary Supplements a Gateway to Doping? A Retrospective Survey of Athletes' Substance Use.

Background : It is proposed that the use of dietary supplements might lead to the use of doping substances. This has been termed the gateway hypothesis. However, within an athletic sample, no research has examined the order in which these substances are consumed and what may explain the progression from dietary supplement use to doping. Objective: To identify whether dietary supplement use precedes doping and examine what moderates the dietary supplement-doping relationship. Methods : Competitive athletes (N=1,081, 42.0% female; Age=29.3±10.8 years) completed an online survey measuring dietary supplement use, doping use, doping subjective norms and age of using a supplement and/or doping substance. Results : Dietary supplement users were 11 times more likely to dope than non-users (OR=11.28, 95% CI = 2.72 to 46.77). Age for first use of a dietary supplement was younger than use of a doping substance (mean difference=-4.5±5.1 years old, p<0.001, d=0.90). Over three-quarters of doping users reported using a dietary supplement first (77.1%), whereas a small proportion of athletes started using dietary supplements and doping at the same time (12.5%) and some used doping substances before using dietary supplements (10.4%). Moderation analysis revealed that dietary supplement users may be more likely to dope because of a more favourable social acceptance of using prohibited substances than non-users. Conclusions : Data suggest that dietary supplement use is more likely to precede doping. However, not all doping users begin with using dietary supplements, which highlights the importance of measuring the temporal order of dietary supplement and doping use in future research.