Citrulline for Fitness: An Evidence-Based Review

Citrulline, a non-essential amino acid, has gained popularity in the fitness community for its potential to enhance exercise performance and recovery. This blog post will examine the latest research on citrulline's effectiveness as a fitness supplement.

What is Citrulline?

Citrulline is an amino acid that plays a role in the urea cycle and nitric oxide production. It's found naturally in some foods, particularly watermelon, but is often taken as a supplement in the form of L-citrulline or citrulline malate [1].

Effectiveness for Fitness

Let's examine the evidence for citrulline's effectiveness in various aspects of fitness:

1. Exercise Performance: A 2020 meta-analysis by Trexler et al. found that citrulline supplementation significantly improved performance in high-intensity strength and power-based exercise [2].

   • Evidence Rating: Moderate to Strong

     • Consistent findings across multiple studies, particularly for high-intensity exercise.

       
       

2. Muscle Soreness and Recovery: A 2010 study by Pérez-Guisado and Jakeman found that citrulline malate supplementation reduced muscle soreness at 24 and 48 hours post-exercise [3].

   • Evidence Rating: Moderate

     • Several studies show positive effects, but more research is needed to confirm these findings across different populations and exercise types.

       
       

3. Aerobic Exercise Performance: The effects of citrulline on endurance exercise are mixed. Some studies show improvements in time to exhaustion and VO2 kinetics, while others show no significant effect [4].

   • Evidence Rating: Limited to Moderate

     • More research is needed to determine the effects of citrulline on different types of aerobic exercise.

       
       

4. Muscle Pump and Vasodilation: Citrulline is often claimed to enhance muscle pump during exercise. While it does increase nitric oxide production, the direct effects on muscle pump are not well-established in research [5].

   • Evidence Rating: Limited

     • More research is needed to confirm these effects in humans during exercise.

       
       

5. Blood Flow and Oxygen Utilization: Some studies suggest that citrulline may improve blood flow and oxygen utilization during exercise, potentially due to its role in nitric oxide production [6].

   • Evidence Rating: Moderate

     • Consistent findings in several studies, but more research is needed to fully understand the mechanisms and extent of these effects.

       
       

It's important to note that while the evidence for citrulline's effectiveness in certain aspects of fitness is promising, individual responses may vary. Factors such as dosage, timing, and individual physiology can all influence the effects of citrulline supplementation.

Mechanisms of Action

Citrulline's effects on exercise performance are thought to be mediated through several mechanisms:

1. Nitric Oxide Production: Citrulline is converted to arginine in the body, which is then used to produce nitric oxide, a vasodilator that can improve blood flow [7].

2. Ammonia Buffering: Citrulline may help buffer ammonia, potentially delaying fatigue during intense exercise [8].

3. ATP Production: Some research suggests citrulline may enhance ATP production during exercise [9].

4. Muscle Protein Synthesis: Citrulline might play a role in stimulating muscle protein synthesis, although this effect is still being studied [10].

   
   

Safety and Side Effects

Citrulline is generally considered safe when used as directed. It's naturally produced in the body and found in foods. Side effects are rare but may include:

• Mild gastrointestinal discomfort

• Changes in urination patterns

  
  

No serious adverse effects have been consistently reported in the literature at recommended doses [11].

Recommended Dosing

Based on current research, the following dosing strategies are generally recommended:

• For acute exercise performance: 6-8 grams of L-citrulline or 8-10 grams of citrulline malate, taken about 60 minutes before exercise [12].

• For daily supplementation: 3-6 grams per day of L-citrulline, which may be divided into multiple doses [13].

  
  

It's worth noting that citrulline malate is often dosed slightly higher than L-citrulline due to the malate component.

Potential Interactions

While citrulline is generally safe, it's important to be aware of potential interactions:

1. Blood Pressure Medications: Citrulline may enhance the effects of blood pressure medications due to its potential to increase nitric oxide production [14].

2. Erectile Dysfunction Medications: Theoretically, citrulline could interact with medications like sildenafil due to its effects on nitric oxide [15].

3. Sodium Nitrate: Combining citrulline with high doses of sodium nitrate could potentially lead to excessive nitric oxide production [16].

   
   

It's always advisable to consult with a healthcare provider before starting any new supplement regimen, especially if you're taking medications or have pre-existing health conditions.

Conclusion

Citrulline appears to be a promising supplement for fitness enthusiasts, with moderate to strong evidence supporting its use for improving high-intensity exercise performance and moderate evidence for reducing muscle soreness. Its effects on aerobic exercise and muscle pump are less clear and require further research.

While generally safe, it's important to use citrulline as directed and be aware of potential interactions with certain medications. As with any supplement, citrulline should be used in conjunction with a balanced diet and appropriate training program, not as a replacement for these fundamental aspects of fitness.

Future research will likely provide more insights into the optimal dosing strategies and potential long-term effects of citrulline supplementation. For now, individuals interested in trying citrulline should consider their specific fitness goals and consult with a healthcare or fitness professional to determine if it's appropriate for their needs.

References

1. Allerton TD, et al. (2018). L-Citrulline Supplementation: Impact on Cardiometabolic Health. Nutrients, 10(7), 921.

2. Trexler ET, et al. (2019). Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis. Sports Med, 49(5), 707-718.

3. Pérez-Guisado J, Jakeman PM. (2010). Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. J Strength Cond Res, 24(5), 1215-1222.

4. Suzuki T, et al. (2016). Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study. J Int Soc Sports Nutr, 13, 6.

5. Gonzalez AM, Trexler ET. (2020). Effects of Citrulline Supplementation on Exercise Performance in Humans: A Review of the Current Literature. J Strength Cond Res, 34(5), 1480-1495.

6. Bailey SJ, et al. (2015). l-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. J Appl Physiol, 119(4), 385-395.

7. Schwedhelm E, et al. (2008). Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism. Br J Clin Pharmacol, 65(1), 51-59.

8. Balderas-Munoz K, et al. (2018). Improvement of skeletal muscle strength in elderly women with chronic heart failure using L-citrulline supplementation. Cardiol J, 25(4), 429-438.

9. Giannesini B, et al. (2011). Citrulline malate supplementation increases muscle efficiency in rat skeletal muscle. Eur J Pharmacol, 667(1-3), 100-104.

10. Jourdan M, et al. (2015). Citrulline stimulates muscle protein synthesis in the post-absorptive state in healthy people fed a low-protein diet – A pilot study. Clin Nutr, 34(3), 449-456.

11. Moinard C, et al. (2008). Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: the Citrudose pharmacokinetic study. Br J Nutr, 99(4), 855-862.

12. Glenn JM, et al. (2017). Acute citrulline malate supplementation improves upper- and lower-body submaximal weightlifting exercise performance in resistance-trained females. Eur J Nutr, 56(2), 775-784.

13. Sureda A, et al. (2009). L-citrulline-malate influence over branched chain amino acid utilization during exercise. Eur J Appl Physiol, 107(2), 221-222.

14. Figueroa A, et al. (2010). Oral L-citrulline supplementation attenuates blood pressure response to cold pressor test in young men. Am J Hypertens, 23(1), 12-16.

15. Cormio L, et al. (2011). Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction. Urology, 77(1), 119-122.

16. Jones AM. (2014). Dietary nitrate supplementation and exercise performance. Sports Med, 44 Suppl 1(Suppl 1), S35-S45.