Comparison of questionnaire vs. standardized interview for nutritional supplement use and third-party testing among NCAA Division I American football athletes

Background Supplement screening questionnaires have not been validated for supplement count accuracy. The objective of this study was to determine the accuracy of self-reported supplement use and third-party tested (TPT) supplement use, compared with an in-person interview as the reference method. The questionnaire also collected behavioral responses, and responses of the validation group were compared to a larger reference group. Results A total of n = 210 NCAA Division I male American football athletes were recruited. Then, n = 40 participated in questionnaire validation (determining mean difference, correlation, and agreement between questionnaire and interview), and n = 170 served as a reference group. The median (IQR) supplement count reported was 4.0 (2.0–6.0) for screener vs. 4.5 (3.0–6.0) in the interview (Z = -3.38, p < 0.001). Screener and interview correlated strongly for supplement count: r = 0.95 (95%CI: 0.90–0.97, p < 0.001), with a mean difference of -0.85 (limits of agreement: -3.51–1.82). For TPT supplement count 2.0 (0.0–4.0), the correlation was moderate r = 0.51 (95%CI: 0.23–0.72, p < 0.001), with a mean difference of -0.05 (limits: -5.50–5.40). Finally, a moderate number of athletes reported purchasing supplements externally, despite having access through their athletic department. Overall, supplement use and behavioral outcomes in the validation group were not significantly different from the reference group. Conclusions Despite significant correlation and strong agreement between methods, the screener modestly underestimated total supplement use versus interviews, with weaker agreement for TPT supplements. Finally, the supplement and TPT supplement use of the validation group was not significantly different from a larger reference group of American football athletes.