Summary: In a small crossover trial in middle-aged and older adults with type 2 diabetes, four weeks of citrulline supplementation improved microvascular endothelial function, muscle microvascular reactivity, and calf muscle strength compared with placebo, alongside higher plasma arginine.
PICO Summary
| Element | Detail |
|---|---|
| Population | 16 adults with type 2 diabetes (aged 53–72; 9 women); double-blind crossover, USA. |
| Intervention | Citrulline 6 g/day for 4 weeks (nitric oxide precursor). |
| Comparison | Placebo, with an 8-week washout between conditions. |
| Outcome | Citrulline improved endothelial function (LnRHI), forearm muscle reactivity (multiple tissue-oxygen-index indices), plasma arginine, and calf muscle strength versus placebo (all p<0.05). Improvements in endothelial function and calf strength were correlated. |
Citrulline, microvascular function & strength in T2D
Crossover RCT · type 2 diabetes · 4 weeks
Four weeks of citrulline raised plasma arginine and improved microvascular function and calf muscle strength versus placebo. Small (n=16), short, surrogate-heavy proof-of-concept.
Expert Commentary
This is a mechanistically coherent small trial linking a plausible pathway to a tangible functional outcome. The rationale is sound: type 2 diabetes is marked by arginine deficiency and impaired nitric-oxide-mediated vasodilation, citrulline is an efficient precursor that raises arginine and nitric oxide, and better microvascular perfusion could plausibly support muscle function. The finding that citrulline improved both endothelial and muscle microvascular reactivity and calf strength, with the vascular and strength gains correlated, ties the mechanism to something patients would actually value, namely physical function in ageing. My reservations are squarely about size and scope. With only sixteen participants over four weeks, this is a short proof-of-concept measuring surrogate vascular indices and isometric strength rather than hard functional endpoints like gait speed, falls, or glycaemic outcomes, and small crossover trials can overstate effects. It is also a supplement study, not a substitute for the fundamentals. Can I use this with my patients? Tentatively and honestly. It is hypothesis-generating and low-risk, so for an older diabetic patient interested in such measures I would not discourage citrulline, while being clear the evidence is preliminary and that resistance exercise and glycaemic control remain the proven routes to preserving muscle and vascular health.
References
Figueroa A, Dillon KN, Levitt DE, Kang Y. Citrulline supplementation improves microvascular function and muscle strength in middle-aged and older adults with type 2 diabetes. Nutrients. 2025;17(17):2790. doi:10.3390/nu17172790