Human pharmacology of a performance-enhancing dietary supplement under resting and exercise conditions

Abstract

AIMS: Dietary supplements (DS) promoted to enhance athletic performance often contain herbal sympathomimetics such as Citrus aurantium (synephrine) and caffeine. We aimed to characterize the pharmacology of a performance-enhancing DS in the setting of exercise. METHODS: Ten healthy adults (three women) aged 20-31 years participated in a three-arm, double-blind, placebo-controlled, crossover study. Subjects ingested one dose of DS (Ripped Fuel Extreme Cut® with 21 mg synephrine and 304 mg caffeine by analysis) under resting conditions and 1 h prior to moderately intense exercise (30 min on cycle ergometer at 75-80% HRmax), with a placebo (PLC)/exercise control. Plasma synephrine and caffeine concentrations were measured over 12 h, and vital signs, serum electrolytes, oxygen consumption and perceived exercise exertion were monitored. RESULTS: No significant adverse events occurred. Synephrine and caffeine pharmacokinetics were unaffected by exercise. Post-exercise diastolic blood pressure was higher after DS (peak mean 71.7 ± 8.7 mmHg) than PLC (63.0 ± 4.9 mmHg) (p = 0.007). There were no substantial treatment-related differences in post-exercise HR, systolic blood pressure, or temperature. Postprandial plasma glucose increased to 121.0 ± 31.6 mg dl-1 with DS and exercise vs. 103.7 ± 25.5 mg dl-1 with PLC and exercise (P = 0.004). No treatment differences in exercise-related oxygen consumption, serum lactate, or insulin were observed. Exercise was rated less difficult with DS than PLC (P = 0.001). CONCLUSIONS: Blood pressure and plasma glucose increased post-exercise with DS use, which could be detrimental in some people. Exercise was perceived as less strenuous after DS, presumably due to the stimulant effects of caffeine. © 2008 The Authors.