The aim of this study was to investigate the plasma dopamine and serum serotonin levels in humans with and without caffeine (CAFF) ingestion during treadmill running exercise. Thirty male volunteers participated in the randomized experiment involving two groups: CON (n = 15, 200 mL of tap water) versus CAFF (n = 15, 3 mg/kg CAFF and 200 mL tap water). After treadmill running, the dopamine level was significantly increased in the CAFF group (P < 0.01) and was significantly higher than in the CON group (P < 0.01). Serotonin was significantly increased in both groups after treadmill running (P < 0.05). However, serotonin levels showed no significant statistical difference between the groups. Prolactin and cortisol were significantly increased in both groups after treadmill running (P < 0.01). However, there was no significant statistical difference between groups. β-endorphin level was significantly increased in the CAFF group at after treadmill running (P < 0.01) and was significantly higher than in CON after treadmill running (P < 0.01). In conclusion, 3 mg/kg CAFF ingestion before treadmill running stimulated dopamine release without inhibiting serotonin, which may reduce central fatigue.
Keywords: Caffeine; dopamine; prolactin; serotonin; β-endorphin.