We found a significant relationship between supplement use and the athletes’ knowledge about the supplements (p < 0.05). Greater knowledge about supplements was associated with less supplement use. Of all respondents, 48% believed that they had an average knowledge about supplements, but three quarters felt that they required further information. Those not taking supplements were more likely to think supplements were associated with health risks (33% vs. 8%, p = 0.03). Most athletes (72%) had access to a nutritionist but underutilized nutritional counseling to choose the best supplement. Coaches (65%) had the greatest influence on supplementation practices, followed by nutritionists (30%) and doctors (%25) after them. Men were more likely to get information from nutritionists, and women from family members or friends and physicians or pharmacists.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3430026/
Or in other words the more dietary supplement usage is associated with less knowledge on what and why they are using said supplements.
Not really too surprising honestly