The new study was published in the Biology. It was the work of a research team associated with a number of universities in Spain.
Is there a synergy to be found?
The goal of the research was to investigate whether there is a synergistic benefit to combining these two ingredients. The physiological argument seems to make sense in that nitrate-rich beetroot extract and citrulline, a non-essential endogenous amino acid, have been shown to be nitric oxide (NO) precursors. Higher NO levels have been associated with greater vasodilation and blood flow with attendant performance benefits.
The researchers designed a four-arm blinded, placebo-controlled study to look into whether this combination could ameliorate markers of exercise induced muscle damage (EIMD) as well as the anabolic/catabolic hormone ratio.
In addition, the authors measured performance via the Cooper test, which is a standardized fitness measurement developed for the US Army. This measures how far a participant can run in 12 minutes.
For subjects, the researchers recruited 32 younger male members of a triathlon club. They ranged in age from 27 up to 41 and all were lean, with body fat percentages ranging from 7% up to 9%. The subjects were divided into four groups of eight participants each: placebo, beetroot supplementation, citrulline supplementation or citrulline plus beetroot. The dosages were 3 grams/day of citrulline and 2.1 grams/day of beetroot extract.
The study extended over nine weeks. The participants all took part in a defined triathlon training plan during the study duration and recorded their dietary intakes via a standardized questionnaire.
The four groups had blood drawn for tests at baseline and at the conclusion of the test. Likewise, they performed one Cooper test at baseline and another at the conclusion of the study.
The study yielded mixed results. The combination supplementation did not reduce markers of EIMD, but it did seem to help participants perform better.
The researchers found no detectable difference between the groups when it came to markers of EIMD, which included measurements of urea, creatinine, AST and ALT (measurements of liver function) and others. In the measures of hormone levels, the BR/CIT combination group showed a positive outcome via lower levels of cortisol and better anabolic/catabolic hormone balance.
The most significant effect, however, was found the Cooper test results. Only the BR/CIT combination group showed a significant improvement in this measure. This group covered an almost 5% greater distance.
“In conclusion, although the combination of 3 g/day of CIT plus 2.1 g/day of BR (300 mg/day of NO3−) supplementation for 9 weeks did not present any benefit for EIMD, it prevented an increase in cortisol and a decline in T/C compared with placebo or isolated supplementation. Moreover, this combination promoted a better distance covered in the Cooper test after 9 weeks of supplementation,” they concluded.
2022, 11(1), 75; https://doi.org/10.3390/biology11010075
Long-Term Combined Effects of Citrulline and Nitrate-Rich Beetroot Extract Supplementation on Recovery Status in Trained Male Triathletes: A Randomized, Double-Blind, Placebo-Controlled Trial
Authors: Burgos J, et al.