L-Citrulline Against Arterial Stiffness

You probably know it from the ingredient list of your pre-workout or amino acid product, l-citrulline. Being a possible precursor of l-arginine it is included in those formulas to increase nitric oxide levels and deliver those "skin bursting pumps" the advertisements brag about.

In a recent study, scientists from Japan (Ochiai. 2010) found that 1 week of l-citrulline supplementation at 5.6g/day effectively reduced arterial stiffness in 15 healthy males:

Compared with the placebo group, baPWV [index of arterial stiffness] was significantly reduced in the l-citrulline group (p<0.01). No significant differences in blood pressure (BP) were found between the two groups, and no correlation was observed between BP and baPWV. The serum nitrogen oxide (NOx, the sum of nitrite plus nitrate) and NO metabolic products were significantly increased only in the l-citrulline group (p<0.05). Plasma citrulline, arginine and the ratio of arginine/asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase (arginine/ADMA ratio) were significantly increased in the l-citrulline group compared with the placebo group (p<0.05, p<0.01, p<0.05, respectively). Moreover, there was a correlation between the increase of plasma arginine and the reduction of baPWV (r=-0.553, p<0.05).

Beyond the reduction in arterial stiffness, these results confirm the hypothesis that l-citrulline effectively increases NO metabolism (probably even more than l-arginine) AND, what's even more important, reduces an endogenous inhibitor of NO synthase, so that more nitric oxide may be produced.