L-Citrulline Supports Vascular and Muscular Benefits of Exercise Training in Older Adults.

Age-associated reduction in endothelial nitric oxide (NO) synthesis contributes to the development of cardiovascular diseases and sarcopenia. L-Citrulline is a precursor of NO with the ability to improve vascular function and muscle protein synthesis. We hypothesize that vascular and muscular benefits associated with oral L-citrulline supplementation might be augmented by concomitant supplementation with exercise training in older adults.

Impact of l-citrulline supplementation on oxygen uptake kinetics during walking.

Supplementation with l-citrulline (Cit) has been shown to improve muscle oxygenation and oxygen uptake kinetics during moderate- to high-intensity cycling in young men. The aim of this study was to test the hypothesis that Cit would improve oxygen uptake kinetics during walking in older and young adults. In a randomized, double-blind study, 26 (15 women, 11 men) adults between the ages of 20-35 years (n = 15) and 64-86 years (n = 11) completed 7-day periods of taking placebo and Cit (6 g/day) in a crossover manner. Participants walked on a treadmill at 40% heart rate reserve while pulmonary oxygen uptake was measured using indirect calorimetry. Net oxygen cost, mean response time (MRT), and the oxygen deficit were calculated before and after each supplement period. There was no significant change (P > 0.05) in net oxygen cost, MRT, or the oxygen deficit after Cit in older adults, while young adults showed a decrease (P = 0.05) in the oxygen deficit after Cit that tended (P = 0.053) to be different than the change after placebo. Sex-stratified analysis revealed that Cit decreased MRT (P = 0.04, Cohen's d = 0.41) and the oxygen deficit (P < 0.01, Cohen's d = 0.56) in men with the change after Cit being greater than the change after placebo (MRT: -4.5 ± 2.1 vs. 3.4 ± 2.1 s, P = 0.01; deficit: -0.15 ± 0.05 vs. 0.01 ± 0.05 L, P = 0.02). All oxygen uptake parameters were unchanged (P > 0.05) following Cit and placebo in women. Cit does not alter the oxygen cost of moderate-intensity walking in young or older adults, but Cit improved the rate of rise in oxygen uptake at exercise onset in men.

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

NEW FINDINGS: What is the central question of this study? Does short-term supplementation with l-citrulline in order to increase l-arginine improve exercise blood flow and peripheral dilatation responses to exercise in older adults? What is the main finding and its importance? l-Citrulline increased femoral blood flow by 11% and vascular conductance by 14% during lower-limb exercise in older men, whereas no changes were observed in older women. This modest improvement in bulk muscle blood flow in older men has implications for altering muscle metabolism that may result in enhanced exercise tolerance in older adults. l-Citrulline (Cit) increases l-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 (13 women and 12 men) 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 analysed separately because of significant sex-by-condition interactions for the change in exercise blood flow and FVC. Plasma [Arg] was increased by 30 and 35% after Cit (P < 0.01) in women and men, respectively, with no change after placebo. Citrulline lowered diastolic blood pressure in men (75 ± 9 versus 71 ± 6 mmHg, P = 0.02), but this variable remained unchanged in women. Blood flow and FVC during exercise at higher workloads were increased after Cit in men (flow, 521 ± 134 versus 584 ± 166 ml min-1 , P = 0.04; FVC, 5.0 ± 1.5 versus 5.8 ± 1.7 m, min mmHg-1 , P = 0.01) but were 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 in men. These results indicate that l-citrulline has a modest effect of improving muscle blood flow during submaximal exercise in older men.

Influence of L-citrulline and watermelon supplementation on vascular function and exercise performance.

PURPOSE OF REVIEW: L-Citrulline, either synthetic or in watermelon, may improve vascular function through increased L-arginine bioavailability and nitric oxide synthesis. This article analyses potential vascular benefits of L-citrulline and watermelon supplementation at rest and during exercise. RECENT FINDINGS: There is clear evidence that acute L-citrulline ingestion increases plasma L-arginine, the substrate for endothelial nitric oxide synthesis. However, the subsequent acute improvement in nitric oxide production and mediated vasodilation is inconsistent, which likely explains the inability of acute L-citrulline or watermelon to improve exercise tolerance. Recent studies have shown that chronic L-citrulline supplementation increases nitric oxide synthesis, decreases blood pressure, and may increase peripheral blood flow. These changes are paralleled by improvements in skeletal muscle oxygenation and performance during endurance exercise. The antihypertensive effect of L-citrulline/watermelon supplementation is evident in adults with prehypertension or hypertension, but not in normotensives. However, L-citrulline supplementation may attenuate the blood pressure response to exercise in normotensive men. SUMMARY: The beneficial vascular effects of L-citrulline/watermelon supplementation may stem from improvements in the L-arginine/nitric oxide pathway. Reductions in resting blood pressure with L-citrulline/watermelon supplementation may have major implications for individuals with prehypertension and hypertension. L-Citrulline supplementation, but not acute ingestion, have shown to improve exercise performance in young healthy adults.

Echinacea-Based Dietary Supplement Does Not Increase Maximal Aerobic Capacity in Endurance-Trained Men and Women.

PURPOSE: To determine if an echinacea-based dietary supplement (EBS) provided at two different doses (a regular dose (RD), 8,000 mg/day, vs. a double dose (DD), 16,000 mg/day) would increase erythropoietin (EPO) and other blood markers involved in improving aerobic capacity and maximal oxygen consumption (VO2max) in endurance-trained men. Secondly, to determine if any sex differences exist between male and female endurance-trained athletes. METHODS: Forty-five endurance athletes completed three visits during a 35-day intervention. Participants were randomized into placebo (PLA; n = 8 men, n = 7 women), RD of EBS (n = 7 men, n = 8 women), or DD of EBS (n = 15 men) for the 35-day intervention period. At baseline, weight, body composition, and VO2max were measured. Blood was drawn to measure EPO, ferritin, red blood cells, white blood cells, hemoglobin, and hematocrit. At the mid-intervention visit, blood was collected. At the post-intervention visit, all measurements from the baseline visit were obtained once again. RESULTS: There was a significant increase in VO2max for endurance-trained men in PLA (increase of 2.8 ± 1.5 ml kg(-1) min(-1), p = .01) and RD of EBS (increase of 2.6 ± 1.8 ml kg(-1) min(-1), p = .04), but not in DD of EBS (p = .96). Importantly, there was no difference in the change in VO2max between PLA and RD of EBS. For endurance-trained women, VO2max did not change in either treatment (PLA: -0.7 ± 1.7 ml kg(-1) min(-1), p = .31; RD of EBS: -0.2 ± 2.4 ml kg(-1) min(-1), p = .80). There were no significant changes in any blood parameter across visits for any treatment group. CONCLUSIONS: This EBS should not be recommended as a means to improve performance in endurance athletes.