Quercetin, a phenolic flavonoid found in small quantities in some fruits and vegetables, is an adenosine receptor antagonist in vitro marketed as a dietary supplement for purported caffeine-like effects. A double-blind, placebo-controlled, between-subjects study was conducted to compare the behavioral effects of quercetin to a central adenosine receptor antagonist, caffeine. Fifty-seven volunteers received either 2000 mg of quercetin dihydrate (a dose estimated based on in vitro receptor binding to be equivalent in potency to 200 mg of caffeine), placebo, or 200 mg of caffeine. One hour later, a 45-minute visual vigilance task was administered. The Profile of Mood States questionnaire was completed before treatment and immediately after vigilance testing. On the vigilance task, caffeine increased the number of stimuli detected (P < 0.02) and decreased the reaction time (P = 0.001). Caffeine increased self-reported vigor and reduced fatigue and total mood disturbance Profile of Mood States scores compared with placebo. Quercetin did not significantly alter any parameter, but values were typically intermediate between caffeine and placebo on those tests affected by caffeine. Quercetin is unlikely to have any effects when consumed by humans in quantities present in the diet or in dietary supplements. Caffeine (200 mg) administration resulted in the expected effects on vigilance and mood.
From the *Department of Nutrition, University of California, Davis; †Clinical Investigation Facility, David Grant USAF Medical Center, Travis AFB, Fairfield, CA; ‡Military Performance Division, and §Military Nutrition Division, US Army Research Institute of Environmental Medicine, Natick, MA.
Received January 11, 2010; accepted after revision June 21, 2010.
Reprints: Harris R. Lieberman, PhD, Military Nutrition Division, US Army Research Institute of Environmental Medicine, 42 Kansas St, Natick, MA 01760-5007 (e-mail: firstname.lastname@example.org).
This work was supported by the US Army Medical Research and Material Command (USAMRMC). The opinions or assertions contained herein are the private views of the author and are not to be construed as official or as reflecting the views of the Army or the Department of Defense. Human subjects participated after giving their free and informed voluntary consent. The investigators adhered to the policies for protection of human subjects as prescribed in Army Regulation 70-25, and the research was conducted in adherence with the provisions of 32 CFR Part 219. Citations of commercial organizations and trade names in this report do not constitute an official Department of the Army endorsement or approval of the products or services of these organizations. Approved for public release; distribution is unlimited.