SAN FRANCISCO— In a recent three-arm, double blind, placebo-controlled, crossover study, after ingesting a dietary supplement with synephrine (Citrus aurantium) and caffeine, exercise was considered less strenuous (Br J Clin Pharmacol. 2008;65(6):833-40) (DOI:10.1111/j.1365-2125.2008.03144.x). Ten healthy adults, aged 20 to 31, ingested one dose of a dietary supplement (as Ripped Fuel Extreme Cut®, from TwinLab) with 21 mg of synephrine (as Advantra Z®, from Nutratech) and 304 mg of caffeine under resting conditions and one hour prior to moderately intense exercise (30 minutes on cycle ergometer), with a placebo exercise control (PLC). Synephrine and caffeine pharmacokinetics were unaffected by exercise. Post-exercise diastolic blood pressure was higher after the supplement than PLC (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 the supplement 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 the supplement than PLC (P=0.001). Blood pressure and plasma glucose increased post-exercise with the supplement use, which could be detrimental in some people.
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