L-Citrulline [Discontinued] by Source Naturals

POSSIBLY EFFECTIVE

• Athletic performance. Small studies show that taking a single oral dose of L-citrulline before anaerobic resistance exercise might reduce exhaustion and improve some performance measures. It is unclear if L-citrulline improves aerobic exercise performance; results are conflicting. Details: A meta-analysis of small clinical trials in healthy trained and untrained adults shows that taking L-citrulline prior to mostly anaerobic exercise marginally reduces perceived exhaustion and muscle soreness when compared with placebo (105965). Another meta-analysis including some of the same clinical studies shows that taking L-citrulline malate before exercise modestly increases performance on resistance exercises by an average of 6% when compared with placebo (105968). Individual studies show mixed benefit and mostly use a single dose of L-citrulline malate 8 grams 1 hour before exercise; other studies used L-citrulline 3.3-6 grams mixed in watermelon juice or sucrose water or L-citrulline malate 12 grams given 1-2 hours before exercise (94966,94957,97395,105965). L-citrulline has also been evaluated for use with aerobic exercise. A small study in healthy young adults taking L-citrulline 9 grams in 3 divided doses over 24 hours or as a single dose of 3 grams 3 hours before a treadmill test does not improve performance, but might reduce time to exhaustion, when compared with placebo (16473). Another small clinical study in healthy adults shows that taking about 6.8 grams (100 mg/kg) of L-citrulline daily for 5 days prior to a cycling trial does not improve time to exhaustion, oxygen uptake, or lactate levels when compared with taking 3 grams of glucose as placebo (105964). However, two small clinical trials in healthy males show that taking L-citrulline 2.4-6 grams daily for 7 days prior to a cycling test improves peak power by 9%, total work by 7%, and cycling time trial performance by 1.5% when compared with placebo (94954,94965). Differences in methods of testing athletic performance, the form and dose of L-citrulline used, and/or the duration of supplementation may explain the mixed results. L-citrulline has also been evaluated in combination with L-arginine. Research in male soccer players shows that taking L-citrulline 1.2 grams and L-arginine 1.2 grams daily for 7 days increases total power output over a 10-minute cycling test and improves subjective perceptions of exertion when compared with placebo (100956).

POSSIBLY INEFFECTIVE

• Sarcopenia. Oral L-citrulline does not seem beneficial for muscle strength in older adults when added to structured exercise. Details: Two small clinical studies in older adults show that taking L-citrulline in conjunction with structured exercise does not improve measures of strength, endurance, speed, or balance when compared with placebo and structured exercise (110146,110148). One study evaluated otherwise healthy adults aged 60-73 years taking L-citrulline 3 grams daily for 6 weeks (110146). The other study evaluated older adults with obesity and an average age of 68.5 years taking a specific L-citrulline product (Citrage) 10 grams daily for 12 weeks (110148).

INSUFFICIENT RELIABLE EVIDENCE to RATE

• Cardiovascular disease (CVD). Although there is interest in using oral L-citrulline for CVD, there is insufficient reliable information about the clinical effects of L-citrulline for this condition.
• Dementia. Although there is interest in using oral L-citrulline for dementia, there is insufficient reliable information about the clinical effects of L-citrulline for this condition.
• Diabetes. It is unclear if oral L-citrulline is beneficial in patients with diabetes. Details: A small clinical study in adults with diabetes who are taking metformin and sulfonylureas shows that adding L-citrulline (Bulk Supplements Co., Ltd.) 3 grams daily before breakfast for 8 weeks reduces average fasting blood glucose levels by 22 mg/dL and glycated hemoglobin by 0.7%, but does not affect lipid levels, when compared with taking a microcrystalline cellulose placebo (105963).
• Erectile dysfunction (ED). It is unclear if oral L-citrulline is beneficial in patients with ED. Details: A small non-randomized crossover study in adults with mild ED shows that taking L-citrulline 1.5 grams daily for one month improves erection hardness from "mild dysfunction" to "normal function" in 50% of patients, compared with only 8% of patients taking placebo (94956). L-citrulline has also been evaluated in combination with other ingredients. A clinical study in middle-aged males with ED shows that taking a specific combination product (Revactin, MD Concepts LLC) containing L-citrulline, muira puama, ginger root, and guarana twice daily for 3 months improves scores related to erectile function and intercourse satisfaction, but does not improve sexual desire or orgasmic function scores, when compared to baseline (103224). The validity of this study is limited by the lack of a placebo control, the use of per-protocol analysis, and a high dropout rate. In fact, 44% of patients withdrew in order to resume use of phosphodiesterase type 5 (PDE5) inhibitors. Another small clinical study in adults with ED living in Japan and using PDE5 inhibitors as needed shows that taking an adjunct 50 mL drink containing L-citrulline 800 mg, a specific fenugreek extract (Testofen) 600 mg, resveratrol 300 mg, and caffeine 40 mg daily for 14 days modestly improves erectile function and satisfaction with intercourse and orgasm when compared with a placebo drink (105966). The validity of this finding may be confounded by the "as needed" use of PDE5 inhibitors, which was not reported throughout the study. Further, in both combination studies, it is unclear if these effects are due to L-citrulline, other supplement ingredients, or the combination.
• Heart failure. Small clinical studies suggest that oral L-citrulline might be beneficial in patients with heart failure. Details: A very small clinical study in patients with heart failure with preserved ejection fraction (HFpEF) shows that taking L-citrulline malate 3 grams daily for 2 months decreases systolic pulmonary arterial pressure by 16% and improves the right ventricular ejection fraction after a stress test by 27% when compared to baseline (94962). The validity of this finding is limited by the lack of a control group. Another small open-label clinical study in patients with heart failure with reduced ejection fraction (HFrEF) shows that taking L-citrulline 3 grams daily for 4 months increases left ventricular ejection fraction by about 20% at rest and 13% during the stress test, and increases the right ventricular ejection fraction by about 15%, both at rest and with the stress test, when compared with no supplementation. This improved the heart failure functional class in 35% of patients (94955).
• Hypertension. It is unclear if oral L-citrulline is beneficial for lowering blood pressure. Details: A small clinical trial in adults with prehypertension shows that taking L-citrulline 2 grams with grape and cranberry polyphenols 548 mg daily for 6 weeks does not reduce mean ambulatory blood pressure when compared with a cellulose placebo (105969). A small crossover study in postmenopausal females with hypertension shows that taking L-citrulline 6 grams as a single dose does not improve systolic or diastolic blood pressure at rest or during 5 minutes of plantar flexion exercise when compared with placebo (110147). The effects of using L-citrulline regularly or in other patients with diagnosed hypertension is unclear.
• Lysinuric protein intolerance. Although there is interest in using oral L-citrulline for lysinuric protein intolerance, there is insufficient reliable information about the clinical effects of L-citrulline for this condition.
• Muscle strength. It is unclear if oral L-citrulline can improve muscle strength when used in conjunction with resistance training. Details: A clinical study in healthy resistance-trained adults shows that taking L-citrulline malate 2 grams daily for 8 weeks in conjunction with resistance training does not further increase lean mass or muscle strength, measured by leg and bench presses, when compared with a cellulose placebo and resistance training (97394).
• Muscular dystrophy. It is unclear if oral L-citrulline is beneficial in patients with Duchenne muscular dystrophy. Details: A small clinical study in adults with Becker muscular dystrophy, a milder form of Duchenne muscular dystrophy (DMD), shows that taking L-citrulline 5 grams with or without metformin 500 mg three times daily for 6 weeks improves 6-minute walking distance and decreases markers of muscle necrosis when compared to baseline (100975). A small clinical study in males aged 6.5-10 years with DMD shows that taking L-citrulline 2.5 grams with metformin 250 mg three times daily for 26 weeks does not appear to slow decline in motor function when compared with placebo. However, this combination seems to slow decline in children with more stable disease, defined as those who can walk at least 350 meters in 6 minutes (100976). The reasons for these disparate results are unclear, but they may be due to the different patient populations, disease severities, doses, and durations of therapy being studied.
• Postoperative pulmonary hypertension. It is unclear if oral citrulline prevents postoperative hypertension in children undergoing heart surgery. Details: A small clinical study in children 6 years of age and younger undergoing congenital heart surgery shows that higher blood levels of L-citrulline might protect against the incidence of postoperative hypertension. L-citrulline blood levels of at least 37 micromol/L immediately after surgery, and at 12, 24, and 36 hours postoperatively, protects against its development. However, supplementation with 1.9 grams/m2 during induction of anesthesia is not necessarily protective (16467).
• Post-polio syndrome. It is unclear if oral L-citrulline is beneficial for patients with this condition. Details: A small clinical study in adults with post-polio syndrome shows that taking L-citrulline 5 grams three times daily for 24 weeks does not improve 6-minute walking distance, motor function scores, muscle strength, or quality of life when compared with placebo (110149).
• Pulmonary hypertension. It is unclear if oral L-citrulline is beneficial in patients with pulmonary hypertension. Details: A very small clinical study in patients with idiopathic arterial pulmonary hypertension or pulmonary hypertension due to Eisenmenger syndrome shows that taking L-citrulline malate 1 gram three times daily for 2 weeks increases 6-minute walking distance by 44 meters and reduces mean pulmonary arterial pressure by 5% when compared with baseline (94963). The validity of these findings is limited by the small study size and the lack of a comparator group.
• Reye syndrome. Although there is interest in using oral L-citrulline for Reye syndrome, there is insufficient reliable information about the clinical effects of L-citrulline for this condition.
• Sickle cell disease. It is unclear if oral L-citrulline is beneficial in patients with sickle cell disease. Details: A small clinical study in children ages 10-18 years shows that taking L-citrulline 90-130 mg/kg daily in 2 divided doses for up to 9 months might reduce neutrophilia and other symptoms when compared with baseline (16463). The validity of these findings is limited by the small study size and the lack of a comparator group. More evidence is needed to rate L-citrulline for these uses.

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POSSIBLY SAFE ...when used orally and appropriately. In clinical trials, L-citrulline has been used with apparent safety for up to 2 months at doses of 1.5-6 grams daily (94954,94956,94961,94962,100974). Doses of up to 15 grams have also been used as single doses or within a 24 hour period (16470,16473).

CHILDREN: POSSIBLY SAFE
when used orally and appropriately. L-citrulline has been used with apparent safety in infants at a dose of 0.17 grams/kg daily (16472). It has also been used in children 6.5-10 years of age at a dose of 7.5 grams daily for 26 weeks (100976). ...when used intravenously and appropriately. An intravenous bolus dose of L-citrulline 150 mg/kg followed by 9 mg/kg/hour for 48 hours has been used safely in children under 6 years of age (16469).

PREGNANCY AND LACTATION:
Insufficient reliable information available; avoid using.

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ANTIHYPERTENSIVE DRUGS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = B Theoretically, concomitant use of L-citrulline with antihypertensive drugs might have additive effects and increase the chance of hypotension.  Details L-citrulline is converted to L-arginine, which can increase nitric oxide and cause vasodilation (7822,16460,16461). However, a meta-analysis of 5 small clinical studies suggests that taking L-citrulline 3-6 grams daily for 1-8 weeks does not lower blood pressure when compared with control (100974).

PHOSPHODIESTERASE-5 INHIBITORS Interaction Rating = Moderate Be cautious with this combination. Severity = Moderate •  Occurrence = Possible •  Level of Evidence = D Theoretically, concurrent use of phosphodiesterase-5 (PDE-5) inhibitors and L-citrulline might result in additive vasodilation.  Details L-citrulline is converted to L-arginine, which can increase nitric oxide and cause vasodilation (7822,16460,16461). Theoretically, taking L-arginine with PDE-5 inhibitors might have additive vasodilatory and hypotensive effects. However, in studies evaluating the combined use of L-arginine and sildenafil for erectile dysfunction, hypotension was not reported (105065).

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General ...Orally, L-citrulline seems to be generally well tolerated.
Most Common Adverse Effects:
Orally: Gastrointestinal discomfort, heartburn.

Gastrointestinal ...Orally, gastrointestinal intolerance, stomach discomfort, and heartburn have been reported with L-citrulline use (94955,94963,94966).

Genitourinary ...Orally, 2 of 25 patients with pulmonary hypertension reported increased urinary frequency and edema while taking 1 gram of powdered L-citrulline in water daily (94963).

Pulmonary/Respiratory ...Orally, 2 of 25 patients with pulmonary hypertension reported cough while taking 1 gram of powdered L-citrulline in water daily (94963).

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