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.
The researchers used Polyphenolics’ MegaNatural BP for its GSE, and an Amazing Nutrition product for its l-citrulline. Neither company provided funding for the research.
Blood flow measures done with sub maximal exercise loadings
The subjects performed exercise tests on a cycling ergometer. One test to assess baseline values was to exhaustion, defined as when the subjects could no longer maintain 60 rpm under steadily increasing load. The other test, which measured the effects of the supplementation interventions, was done at 30%, 60% and 80% load. The 30% and 60% segments were done sequentially, and after a 15 minute rest, the 80% test was performed. All of the segments were 5 minutes in length.
The researchers measured systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and oxygen consumption (VO2) and enhance stroke volume (SV) and cardiac output.
Additive hypothesis doesn’t pan out
The researchers did not find the additive effect they were looking for.
“Our study indicates that GSE, L-citrulline, and a combination of GSE and L-citrulline supplementations had no significant changes in SBP, DBP, and MAP across the work-loads compared with placebo,” the researchers wrote. They noted that one possible reason why this result did not match previous results for these substances, especially for GSE, was that previous studies were done with prehypertensive individuals. In other words, GSE might help get someone back to a healthy blood pressure baseline, but didn’t show additional improvements from there.
Oxygen cost finding
However, they did see in improvement in the oxygen cost of exercise, both for the GSE alone and in combination, which is an important finding in and of itself.
“Taken together, these findings suggest that GSE can act as a dietary nutraceutical capable of improving oxygen delivery to exercising skeletal muscles. Future research is still needed to investigate the effect of GSE supplementation on exercise performance (i.e., time to exhaustion or time trial performance),” they concluded.
Source: Journal of Dietary Supplements
doi.org/10.1080/19390211.2021.2023246
Effect of Combined Grape Seed Extract and L-Citrulline Supplementation on Hemodynamic Responses to Exercise in Young Males
Authors: Shariffi B, et al.
Sports & Active Nutrition Summit 2022
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