# L-Citrulline: A Non-Essential Amino Acid with Important Roles in Human Health
## 8 Studies with Citrulline from Natural Sources: Watermelon
In another previous study, acute watermelon juice consumption (providing 1.17 g of CIT per 500 mL) and enriched watermelon juice (6 g of CIT per 500 mL) attenuated moderate muscle soreness after 24 h of exercise in untrained healthy subjects participating in high-intensity exercise intervals, although performance was unimproved [138]. In another study, with healthy non-athletic adults, no significant differences were found among different sport supplements in blood lactate, heart rate recovery or post-exercise muscle soreness. However, when females had acute watermelon juice supplementation (355 mL) it prevented increased diastolic blood pressure and post-exercise systolic pressure; such responses were not obtained in men [139]. On the other hand, chronic supplementation of watermelon juice (16 days with 300 mL/day of watermelon juice concentrate, providing a daily CIT dose of \(\sim\)3.4 g/day) with respect to placebo showed a higher skeletal muscle oxygenation index in watermelon juice conditions than in placebo and control conditions, although time-to-exhaustion during the severe-intensity exercise test did not differ significantly between conditions, with systolic blood pressure being higher in watermelon juice conditions [140]. Moreover, another study of chronic supplementation of frozen watermelon pure (two weeks ingesting 980 mL/day 0.2 g/kg carbohydrate with 1.47 g CIT, 0.465 g Arg versus a 6% carbohydrate beverage every 15 min throughout the time trials) in 20 trained cyclists, found that exercise performance was similar under watermelon and placebo conditions, and that the highest RPE was observed under watermelon conditions [141]. In line with this, [PERSON] et al. [51] did not find improved exercise performance following one dose of CIT (6 g) or watermelon juice (\(\sim\)1.0 g CIT) taken 1-2 h before exercise in healthy male subjects. A systematic review [142] to evaluate the effect of CIT watermelon supplements (1.17-6 g of CIT obtained from watermelon) on the post-exercise RPE and muscle soreness has recently been published. In that review, the supplementation time frame was limited to 2 h before exercise. The types and number of participants, types of exercise tests performed, supplementation protocols, and primary (RPE and muscle soreness) and secondary (blood lactate level) study outcomes were extracted from the identified studies. The study involved 13 eligible articles (10 of them using CM and 3 using watermelon supplementation) and a total of 206 participants. The most frequent dosage used in the studies was 8 g of CM. CIT watermelon supplementation significantly reduced RPE (\(n=7,p=0.03\)) and muscle soreness 24-h and 48-h after post-exercise (\(n=7,p=0.04\); \(n=6,p=0.03\), respectively). However, CIT from watermelon supplementation did not significantly reduce muscle soreness 72-h post-exercise (\(n=4,p=0.62\)) or lower blood lactate levels (\(n=8,p=0.17\)). As the main conclusion, CIT supplements from watermelon significantly reduced post-exercise RPE and muscle soreness, without affecting blood lactate levels. This is especially recommended for power and strength athletes to adequately recover and subsequently train at their desired intensity level. Different factors probably influence the ergogenic effect of CIT on perceived exercise improvement, which makes the results in studies analyzing CIT responses somewhat controversial and so warrants further study in the future. Other benefits of watermelon consumption have been related to cardiovascular risk factors. [PERSON] et al. [143] found a reduction in low-density lipoprotein and plasma total cholesterol when volunteers with dyslipidemia were supplemented daily with 6 g of watermelon extract for 42 days. [PERSON] et al.