The new study was the work of researchers associated with California Baptist University in Riverside, CA. The paper was published online this week in the Journal of Dietary Supplements.
The aim of the study was to discover whether grape seed extract (GSE) could improve oxygen delivery to working muscles via vasodilation, and whether there was an additive benefit when GSE was combined with L-citrulline.
Both ingredients have history of sports nutrition research
L-citrulline is a legacy sports nutrition ingredient. Researchers first began looking at the performance benefits of this amino acid in the 1980s. The primary benefit has been postulated as a boost in nitric oxide levels in the body, which is associated with increased blood flow via dilated peripheral blood vessels.
Grape seed extract is a more recent entrant into the supplementation scene. Studies on the blood flow effects of GSE date to the late 1990s. Among the early developers of GSE products was California firm Polyphenolics, which was using leftover material from the production of Gallo-branded wines. Another developer is Indena, which recently published a study showing significant cardiovascular benefits for its offering.
To study whether the two products had a synergistic effect, the researchers designed a four arm, double blind, placebo controlled crossover study. They recruited 11 healthy, lean young men who all had normal blood pressure. The subjects took one of four interventions for a week, with a week-long washout period in between. The four interventions were a placebo, a 6 gram dose of l-citrulline, l-citrulline along with 600 mg of GSE, and GSE alone.