Effects of Vitamin B12 and Natural Orange Extract, and Their Combination on Physical and Mental Performance

A triple-blind, randomized, crossover clinical trial will be conducted with three experimental phases (vitamin B12 + natural orange extract, natural orange extract, vitamin B12) and one control phase (placebo), including evaluations of the acute effect after a loading phase (three intakes, one per day including the test day). Participants The sample will consist of 20 well-trained male cyclists (road, MTB, or triathlon), training 3-6 sessions per week, aged between 18 and 45 years. The inclusion criteria will be: * Healthy male (to be certified through medical examination and health analysis). * Aged 18-45 years. * Well-trained (3-6 training sessions per week). * Habitual consumer of citrus fruits (orange, mandarin, lemon, or grapefruit, either whole or as juice). Tests * General health analysis: A general blood test (including standard biochemistry and complete blood count) will be performed during the recruitment phase. * Medical examination: A cardiorespiratory assessment at rest will be conducted to rule out any underlying pathology. * Specific performance-related blood analysis: Conducted at four time points (total of eight measurements): baseline during recruitment, pre- and post-test in each condition (supplement / placebo). Parameters will include: complete blood count, ferritin, CK, LDH, vitamin B12, transaminases, reticulocytes, homocysteine, C-reactive protein, IL-6, methylmalonic acid, holo-transcobalamin II, 8-OHdG (8-hydroxy-2'-deoxyguanosine), dopamine, serotonin, and Brain-Derived Neurotrophic Factor (BDNF). * Anthropometry: Determination of body composition parameters to characterize the sample. * Wingate test: Conducted using the standard load protocol, consisting of five maximal 30-second sprints with 3-minute recovery intervals between repetitions. * Mental fatigue test using light-based reaction tasks: The time required to complete a light reaction sequence will be measured before and after the fatigue protocol. * Genetic test: A saliva sample will be collected to analyze genetic profiles related to food intolerances and vitamin absorption. The objective is to identify potential explanations for interindividual differences in absorption capacity.