Barrack, MT, Fredericson, M, Dizon, F, Tenforde, AS, Kim, BY, Kraus, E, Kussman, A, Singh, S, and Nattiv, A. Dietary supplement use according to sex and Triad risk factors in collegiate endurance runners. J Strength Cond Res 35(2): 404–410, 2021—This cross-sectional study evaluated the prevalence in the use of dietary supplements among elite collegiate runners among 2 NCAA Division I cross-country teams. At the start of each season from 2015 to 2017, male and female endurance runners were recruited to complete baseline study measures; the final sample included 135 (male n = 65, female n = 70) runners. Runners completed a health survey, web-based nutrition survey, and Triad risk assessment. The prevalence of dietary supplement use and Triad risk factors, including disordered eating, low bone mass, amenorrhea (in women), low body mass index, and stress fracture history, was assessed. A total of 78.5% (n = 106) runners reported taking 1 or more supplements on ≥4 days per week over the past month, 48% (n = 65) reported use of ≥3 supplements. Products used with highest frequency included multivitamin/minerals 46.7% (n = 63), iron 46.7% (n = 63), vitamin D 34.1% (n = 46), and calcium 33.3% (n = 45). More women, compared with men, used iron (61.4 vs. 30.8%, p < 0.001) and calcium (41.4 vs. 24.6%, p = 0.04); men exhibited higher use of amino acids and beta-alanine (6.2 vs. 0%, p = 0.04). Runners with bone stress injury (BSI) history, vs. no previous BSI, reported more frequent use of ≥3 supplements (61.5 vs. 32.8%, p = 0.001), vitamin D (49.2 vs. 19.4%, p < 0.001), and calcium (47.7 vs. 19.4%, p = 0.001). Low bone mineral density was also associated with higher use of vitamin D and calcium. Most runners reported regular use of 1 or more supplements, with patterns of use varying based on sex, history of BSI, and bone mass.