Benefits of quercetin, citrulline combination for cyclists unclear: Study

29-Oct-2024 - Last updated on 29-Oct-2024 at 11:27 GMT

Co-supplementation with ergogenic aids quercetin and citrulline may not have additive benefits during timed trials in highly trained cyclists, but each individually improved maximal oxygen consumption (VO2), according to a recent study.

"QCT + CIT does not seem beneficial for 20-km TT performance; further exploration with a focus on an increase in cycling duration or QCT+CIT combined with additional polyphenols may amplify any perceived bioactive or metabolic effects on cycling performance," the team of U.S.-based university researchers wrote. "The efficacy of QCT + CIT supplementation to improve cycling performance remains ambiguous."

Published in the Journal of the International Society of Sports Nutrition, the research was supported by the Food and Nutrition Service. Trisha VanDusseldorp, senior director of clinical research at Bonafide Health and co-author on the paper, secured funding for the supplements used in the study.

Nutritional ergogenic supplements

Used to optimize time trial (TT) in cycling, nutritional ergogenic supplements can help to improve cycling efficiency, ATP production and oxygen consumption, among other benefits. Prior studies have analyzed the benefits of quercetin (QCT) or citrulline (CIT) separately.

QCT, a plant pigment found in kale, red onions, red wine, elderberries and other fruits and vegetables, is rich in polyphenols, antioxidants and flavanols. In athletes, it has been shown to improve oxygen consumption and VO2 kinetics.

CIT, a nonessential amino acid, is found in watermelon and formed from arginine. It has strong anti-inflammatory and antioxidant properties as well as benefits for oxygen uptake and recovery.

Study details

The randomized, double-blind placebo-controlled study consisted of 50 participants: 42 men and 8 women. All participants were tier 2 cyclists (in a 6-tier framework), and women were tested during their follicular phase due to hormone stability.

Participants were randomly assigned to one of four groups: Group 1 (QCT 500 mg, CIT 3,000 g), Group 2 (QCT 500 mg), Group 3 (CIT 3,000 mg) and Group 4 (placebo). They consumed their assigned supplements (or placebo) twice daily for 28 day and performed a 20-km cycling time-trial race pre- and post-supplementation. Power, VO2, RER, REP, heart rate and oxygen consumption were recorded.

The study did not observe potential benefits of QCT+CIT supplementation on TT performance and several performance measures; however there was an improvement in VO2 from pre-to-post-supplementation in QCT and CIT groups, but not in the QCT+CIT and PL groups.

“Our results suggest that combining QCT and CIT may alter the perceived effort at the start (0 km) and the end of a race (20 km), indicating that the supplement may have increased the level of effort the participants could maintain during the TT,” the researchers added.

They also noted that no other studies have investigated QCT, CIT or the combination of the two on oxygen consumption during a 20-km time trial. The results show that while QCT did not enhance the time trial performance, it did increase VO2 over the time of the study.

“Based on the present findings and conflicting previous results, we contend that it is premature to preclude any beneficial effects of QCT supplementation on perceptual responses during a self-paced, competitive TT event,” the researchers wrote.

Source: Journal of the International Society of Sports Nutrition 2024, 21(1)
doi: 10.1080/15502783.2024.2416909
“The effect of quercetin and citrulline on cycling time trial performance”
Authors: Kurtz, J.A., et al.