What is Citrulline?
Citrulline is an amino acid first found and isolated in watermelon. The name citrulline comes from the Latin word Citrullus, which means watermelon. It is classified as a nonessential amino acid, meaning that your body can create its own. Nonetheless, you can boost your levels by eating citrulline-containing foods or taking dietary supplements rather than relying on your body’s production alone.
Citrulline is used to increase nitric oxide production in the body. Citrulline does not increase nitric oxide directly but instead causes an increase in Arginine and Ornithine plasma levels. Arginine and ornithine lead to the rise in nitric oxide within the body.
Citrulline, especially citrulline malate, is absorbed by the body much more readily than arginine. This absorbed citrulline gets converted by the kidneys into arginine and ornithine.  Studies show that citrulline might help treat hypertension, intestinal problems, liver disease, Parkinson’s disease and certain dementias. Some people also take citrulline to build muscles and improve athletic performance.
What is the best form of L-citrulline?
Citrulline malate is the best form of citrulline. It is better absorbed and has higher bioavailability when taken orally. L-citrulline and citrulline malate are the two primary forms of citrulline commonly found in supplements.
This form of citrulline is the natural form found in certain foods, such as watermelon. It is also the form that the body makes.
Citrulline malate is L-citrulline with malate added to it. The addition of the malic acid increases the absorption and bioavailability of the ingested citrulline.
Benefits of Citrulline
Hypertension is a condition of sustained elevated blood pressure. Numerous studies have demonstrated a 4 to 16 percent decrease in blood pressure after a few weeks of supplementation with citrulline. The average citrulline dosage used in the studies was 3 grams per day. 
Improve performance and endurance
A study using cyclists showed that citrulline supplementation could increase the cyclists’ power output. the increased power output allowed them to perform a cycle ergometer trial faster.  The researchers concluded that the performance increase was due to increased plasma arginine levels, resulting in increased nitric oxide production.
Another study using cyclists showed that citrulline could increase cyclists’ endurance. The study showed that endurance was improved on average by 12 percent; this meant that those cyclists who took citrulline could cycle for 12% longer. 
Growth Hormone (GH)
Growth hormone stimulation is an exciting benefit for athletes, bodybuilders, or anyone looking for increased muscle mass. The growth hormone release seen with citrulline is an indirect benefit. The conversion of citrulline into ornithine leads to growth hormone stimulation. Ornithine stimulates growth hormone release. 
In addition to stimulating the release of growth hormone, which can help to increase muscle growth.  Citrulline can increase muscle mass and help to change body composition in a positive direction of less fat and more lean muscle mass. A study done using rats proved this, as it showed that rats given citrulline had 9 percent more lean muscle mass after supplementing with 1 gram per day for 12 weeks. 
Healing and Recovery
Citrulline is proven to help speed healing and recovery. A study done looking at the healing effects of citrulline and arginine showed that both had healing benefits for broken bones and fractures. The study showed that citrulline had the best healing advantage and significantly sped up the healing process of bone. The researchers speculate that the benefit citrulline provides might be derived from the formation of new blood vessels that ultimately bring more nutrient and oxygen-rich blood to the healing bone.  Since citrulline increases the serum levels of ornithine, we might also want to conclude that studies showing ornithine speeds healing and recovery might also apply to citrulline. 
Muscle recovery improves, and soreness experienced after exercise or training decreases. A study using 8 grams of citrulline malate correlated with a 40 percent reduction of delayed muscle onset soreness (DOMS) after 24 hours and 48 hours. 
Side Effects of Citrulline
There is no documented toxicity from citrulline supplementation. The side effect profile is also excellent. Studies done using large bolus doses of citrulline have shown that it is well tolerated even at high doses of 15 plus grams. 
Unlike arginine and ornithine, which do not get absorbed well by the body. They pass into the colon and cause diarrhea due to the osmotic pressure they cause, drawing water into the colon. Citrulline malate is absorbed well and thus does not cause the same osmotic-related diarrhea when taken in large doses. Gastrointestinal side effects can happen but usually only with substantial bolus doses well above 15 grams.
The most effective dosage for citrulline supplementation is between 3 to 15 grams. The dosage can vary depending on the type of citrulline you are using and why you are supplementing with it. Users should adjust their dosage based on how their body reacts to it. Also, adjustments are made based on activity level, age and weight.
What is the Citrulline dosage for a pump?
The best citrulline dosage to induce a pump is 8 grams taken one hour before a workout. This dosage is large enough that most users will see a significant rise in nitric oxide levels and consequently a nice muscular pump in their working muscles during their workout. If 8 grams does not produce the desired vascular pump, users can increase the dose to 15 grams. Fifteen grams is the limit of the tested dosages without any noted side effects. 
When is the best time to take citrulline?
The best time to take citrulline is 30 to 60 minutes before working out.  Taking pre-workout will increase nitric oxide levels and improve performance and recovery.
How long does citrulline last?
The half-life of oral citrulline is 60 minutes post-administration. Even though its half-life is 60 minutes does not mean its effects wear off after 60 minutes. Remember, citrulline’s primary mechanism increases arginine and ornithine blood levels. These increased arginine and ornithine levels lead to the benefits such as increased nitric oxide, etc. By the 60 minute mark, the body has already converted most of the oral dose into these other two amino acids.
Citrulline was first discovered in watermelon, and this melon contains the highest amounts found naturally.
Other sources include:
- Casaba melon
- Horned melon
- Bitter melon
- Mouse melon
What fruit has the most citrulline?
The fruit with the highest citrulline content is the yellow watermelon. The yellow watermelon contains 3.5mg of citrulline per gram. The table below shows the fruits with the highest citrulline content per gram.
|Yellow watermelon||3.5mg per gram|
|Orange watermelon||1.8mg per gram|
|Red watermelon||1mg per gram|
|Cucumbers||0.146mg per gram|
- Citrulline and the gut – PubMed (nih.gov)
- Effect of L-arginine or L-citrulline oral supplementation on blood pressure and right ventricular function in heart failure patients with preserved ejection fraction – PubMed (nih.gov)
- Combined whole-body vibration training and l-citrulline supplementation improves pressure wave reflection in obese postmenopausal women – PubMed (nih.gov)
- Oral nitrate and citrulline decrease blood pressure and increase vascular conductance in young adults: a potential therapy for heart failure – PubMed (nih.gov)
- Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study – PubMed (nih.gov)
- l-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans – PubMed (nih.gov)
- Ornithine ingestion and growth hormone release in bodybuilders – ScienceDirect
- Citrulline Supplementation Induces Changes in Body Composition and Limits Age-Related Metabolic Changes in Healthy Male Rats | The Journal of Nutrition | Oxford Academic (oup.com)
- v039a12.pdf (ecmjournal.org)
- Effect of Supplemental Ornithine on Wound Healing – ScienceDirect
- Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness – PubMed (nih.gov)
- Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: the Citrudose pharmacokinetic study – PubMed (nih.gov)
The information contained within this article is not to be taken as medical advice. always consult your doctor before starting any supplement.