The Study
Acute effect of citrulline malate on flow-mediated dilation and serum pharmacodynamics in healthy young males
This study gave people a supplement and checked if it made their blood vessels open up more. It found that the supplement did raise certain chemicals in the blood, but didn’t actually make the blood vessels widen. So we know the supplement does something in the body, but that something didn’t lead to the result they were hoping for.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
This study tested if taking a citrulline supplement (found in watermelon) makes your arteries open up more right after you take it.
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 568 / 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.
- 1Even though the body made more of the chemicals that should widen blood vessels, it didn't happen in healthy, active young men at rest — their vessels were already working well.
- 2After taking 6g or 12g of citrulline, blood levels of helpful chemicals went up by 50–100%, but the artery didn't get any wider (FMD didn't change).
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Frontiers in Physiology
Year
2026
Authors
Johan Grannes, Nigel A. Callender, Adam M. Gonzalez, J. Hisdal, F. T. Vårvik, T. Bjørnsen
Related Content
Claims (10)
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.
When healthy young men take citrulline malate, their blood shows higher ratios of arginine to two molecules that inhibit nitric oxide production, even though blood vessel function does not change measurably.
Citrulline malate improves blood vessel function only in certain situations—such as in people with poor blood vessel health, during exercise, or after long-term use—but does not improve blood vessel function in healthy young men at rest, even though it increases molecules involved in blood vessel relaxation.
Taking 6 or 12 grams of citrulline malate does not increase blood vessel dilation in healthy young men at rest, even though it raises levels of citrulline, arginine, and ornithine in the blood.
In healthy young men who exercise regularly, citrulline malate does not improve blood vessel dilation because their arteries are already larger and less responsive to vasodilatory stimuli.
Citrulline malate does not improve blood vessel function in healthy young men at rest, but it may improve blood vessel function when taken regularly, during exercise, or in people with existing blood vessel problems.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.