Does L-citrulline supplementation improve exercise blood flow in older adults?

Abstract

L-citrulline (Cit) increases arginine (Arg), the primary substrate for nitric oxide biosynthesis. We tested the hypothesis that muscle blood flow during exercise would be enhanced by Cit supplementation in older adults. Femoral artery blood flow was measured during calf exercise using Doppler ultrasound, and vascular conductance (FVC) was calculated in 25 older adults (13W, 12M) before and after 14 days of Cit (6 g day⁻¹) and placebo (maltodextrin) in a randomized, double-blind, crossover study. Plasma [Arg] and resting blood pressure were also measured before and after each condition. Women and men were analyzed separately due to significant sex-by-condition interactions for the change in exercise blood flow and FVC. Plasma [Arg] was increased by 30% and 35% following Cit (P < 0.01) in women and men, respectively, with no change after placebo. Citrulline lowered diastolic blood pressure in men (75 ± 9 vs. 71 ± 6 mmHg, P = 0.02), but remained unchanged in women. Blood flow and FVC during exercise at higher workloads were increased following Cit in men (flow: 521 ± 134 vs. 584 ± 166 mL min⁻¹, P = 0.04; FVC: 5.0 ± 1.5 vs. 5.8 ± 1.7 mL min mmHg⁻¹, P = 0.01) but was not different after placebo. These variables were not altered by Cit in women. Adjusting for baseline diastolic blood pressure removed (P = 0.10) the difference in FBF and FVC following Cit men. These results indicate that L-citrulline has a modest effect of improving muscle blood flow during submaximal exercise in older men.

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