Harden, LM, et al. “The Effects of an L-Methionine Combination Supplement on Symptoms of Upper Respiratory Tract Infections and Performance in Ultramarathon Runners Before, During and After Ultra-Endurance Exercise”. South African Journal of Sports Medicine, vol. 16, no. 1, Dec. 2004, pp. 10-16, doi:10.17159/2078-516X/2004/v16i1a188.