The Study
Effect of L-Citrulline Supplementation on Endothelial Function and Body Composition in Post-COVID-19 Syndrome: A Randomized Clinical Trial
This study gave some people a supplement and others a placebo, then saw who felt better or had changes in their blood. Because they were randomly assigned, we can guess the supplement might have caused the changes—but it’s not 100% sure because everyone knew who got what.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
After getting very sick from COVID, some people feel weak and can't walk as far. This study tested if taking a daily amino acid called L-citrulline helps them recover better.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 574 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Walking 141 meters farther is meaningful—it’s like adding a full city block to your daily walk.
- 2The drop in ICAM-1 suggests less blood vessel inflammation, which may help circulation.
- 3People who took L-citrulline walked 141 meters farther in 6 minutes and had a 32.6 ng/mg drop in ICAM-1 (a marker of blood vessel inflammation).
- 4Other measures like muscle strength and body fat didn't change.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Nutrients
Year
2026
Authors
Salgado-Fernández María Fernanda, Orea-Tejeda Arturo, Sierra-Vargas Martha Patricia, González-Islas Dulce, Debray-García Yazmín, Aztatzi-Aguilar Octavio Gamaliel, Galicia-Amor Susana, Hernández-López Samantha, Renteria-Serralde Getsemani, Cruz-Gijón Gabriela, Maldonado-Vargas Valeria
Related Content
Claims (6)
When citrulline is metabolized, it leads to increased nitric oxide production in blood vessel lining cells, which causes blood vessels to widen and improves oxygen delivery to skeletal muscle.
In adults recovering from severe COVID-19 who were hospitalized, taking 4 grams of L-citrulline daily for three months lowers ICAM-1 protein levels by about 32.6 ng/mg and increases the distance walked in six minutes by about 141.2 meters.
Taking 4 grams of L-citrulline daily for three months does not change measures of body composition such as muscle mass, phase angle, or handgrip strength in adults recovering from severe COVID-19, compared to those receiving standard care without the supplement.
In adults recovering from severe COVID-19, taking 4 grams of L-citrulline daily for three months lowers ICAM-1 but does not lower endothelin-1, sE-selectin, or VCAM-1.
After severe COVID-19, people improve their ability to walk six minutes whether or not they take L-citrulline, showing that recovery from the illness and standard medical care alone can lead to meaningful functional gains.
Taking 4 grams of L-citrulline daily for three months does not change plasma nitrite levels in adults who have recovered from severe COVID-19.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.