L-Citrulline, also known as Citrulline, is a naturally occurring neutral non-essential amino acid in our bodies.
It was first identified in the juice of watermelon.
Fitness and bodybuilders regularly consume citrulline amino acid to increase exercise performance. In many supplements, it is marketed as a “pump-inducing” ingredient because it is shown to relax blood vessels, which improves blood flow.
Several benefits of citrulline have been the focus of many research studies. This article provides an overview of citrulline, its benefits, dosage, and safety.
Citrulline supplement types
In research, citrulline has been used in two types of supplements. These are:
- L-citrulline extract
- Citrulline malate
L-citrulline from a food source such as watermelon is available in the market. The supplement contains purified citrulline powder extract from food.
Citrulline malate is a commercially available supplement frequently used by bodybuilders and athletes.
It combines citrulline with malate (1:1 ratio). Malate is a salt of malic acid. It is produced in mitochondria during the Krebs cycle. Malate also increases ATP production, thus, enhancing energy levels (1).
And it may also decrease lactic acid production to improve recovery (2).
The combination of citrulline and malate can improve the effects of citrulline. Therefore, it is commonly promoted in bodybuilding supplements.
Why citrulline is important?
One of the vital roles of citrulline is to increase the bioavailability of L-arginine, also known as arginine. In the body, citrulline either from watermelon or in supplement form is converted to arginine in the urea cycle.
Citrulline is an intermediate in the urea cycle for the production of arginine from ornithine amino acid.
It is also produced in the stomach, released in the blood, and converted into arginine in the kidneys (3).
Why arginine is indispensable? Arginine is a semi-essential amino acid. It is produced naturally in the adult human body, but it produces in low amounts in children, the elderly, and critically ill patients.
Arginine is converted into nitric oxide (NO) by an enzyme called nitric oxide synthase. Therefore, it is a significant producer of nitric oxide.
Thus, Citrulline is pivotal in increasing nitric oxide in the body by increasing arginine.
Interestingly, citrulline supplementation is more efficient in increasing arginine bioavailability in the body and muscle than arginine supplementation itself. Both watermelon consumption or citrulline powder has this effect (4).
Arginine is produced in the liver and kidneys. The arginine produced in the liver is readily broken down by the arginase enzyme, reducing its bioavailability. In the kidneys, citrulline produces arginine, which escapes degradation and becomes bioavailable for nitric oxide production (5).
Thus, citrulline is superior to arginine in increasing nitric oxide in the body (6).
Food sources of citrulline
Foods are a poor source of citrulline. But it is found in the highest amounts in watermelon. The name citrulline comes from Citrullus lanatus, the biological name of watermelon.
The amount of citrulline depends on the type of watermelon (7).
On average, 1 liter of watermelon juice provides 2.33 g of citrulline (8).
Citrulline foods include:
- Bitter melon
- Bottle gourd
- Dishrag gourd
- Wax gourd
Citrulline enhances nitric oxide
Nitric oxide plays a significant role in human health because it is a part of major cell signaling pathways.
Nitric oxide is important for the immune system, thus, plays a significant role in infections and controlling diseases (9).
Oxidative stress severely reduces nitric oxide availability, which results in further dysfunction of the blood vessel. Therefore, nitric oxide levels are considered an indicator of oxidative stress (10).
Nitric oxide dysfunction also leads to diseases such as cardiovascular diseases and atherosclerosis.
Dementia patients have low levels of citrulline and arginine compared to healthy individuals (12).
Nitric oxide is also essential for glucose metabolism, and reduction of nitric oxide availability increases the risk of type 2 diabetes mellitus (13).
Citrulline availability increases nitric oxide production.
In healthy adults, the use of citrulline (6 g per day for 7 days) increased nitrite levels by 22% compared to no use (14).
In adults with arterial stiffness, the use of citrulline (5.6 g per day for 7 days) improved nitrites by 37% (15).
A combination of citrulline and glutathione supplement improves nitric oxide production compared to citrulline alone (16).
Patients with a genetic disorder called lysinuric protein intolerance (LPI) have arginine deficiency. The use of arginine therapy increases nitric oxide levels and also improves blood vessel structure (17). The study did not test the effects of citrulline which is more effective in improving nitric oxide.
Citrulline improves the availability of nitric oxide, which has several health benefits.
Citrulline improves cardiovascular function
The endothelium is a thin layer present inside the heart and blood vessels. It plays a vital role in maintaining heart and blood vessels in good condition.
Citrulline improves vasodilation function. Vasodilation is the process of relaxation of blood vessels, which widens the vessels and increases blood circulation.
As mentioned earlier, citrulline promotes vasodilation by increasing the amount of nitric oxide gas in blood vessels (18).
With aging, the vasodilation function is impaired. In older adults, the use of citrulline may improve endothelial and vasodilation function (19).
Citrulline may improve cardiovascular function by improving endothelial function by increasing nitric oxide levels
Citrulline lowers blood pressure
Current research shows that citrulline may reduce blood pressure in people with high blood pressure, but not in individuals with normal blood pressure.
Citrulline supplementation (6 g per day for 8 weeks) lowered Systolic BP and Diastolic BP In obese menopausal women (20).
The use of citrulline (3 g per day for 8 weeks) significantly reduced blood pressure in heart failure patients (21).
Watermelon extract supplementation (6 g per day for 6 weeks) lowers systolic and diastolic blood pressure in prehypertension and hypertensive individuals (22).
Citrulline may lower blood pressure in people with normal blood pressure (23).
Citrulline supplementation in young healthy individuals did not lower resting blood pressure, but it lowered blood pressure in response to exercise (24).
This suggests that using citrulline can be beneficial in lowering blood pressure increases due to exercise.
In conclusion, several studies showed that the use of citrulline or watermelon extract can lower blood pressure in people with high blood pressure. Most of these studies used 6 g per day for 6-8 weeks.
Citrulline may enhance exercise performance
Citrulline is considered an ergogenic aid i.e. improves physical performance during exercise. Its use is becoming popular because of its exercise performance-enhancing effects.
Most of the citrulline benefits come from, its role in improving nitric oxide amounts.
An increase in nitric oxide improves exercise performance (25).
Nitric oxide enhances exercise performance by improving oxygen availability to skeletal muscles (26). This leads to better utilization of oxygen in the muscles and increased exercise performance.
High-intensity exercise increases blood ammonia level, which in turn increases lactate, causing increased fatigue. The use of citrulline malate improves exercise performance and reduces fatigue (27).
One study found that the use of citrulline malate 8 g intake with weight training decreased muscles soreness and fatigue (28).
The use of Citrulline immediately before exercise does not improve high-intensity exercise performance or weight training.
A study found that the intake of 6 g citrulline right before training (1-2 h) could not improve recovery or exhaustion (27).
Research also shows that the use of 6 g citrulline before exercise does not reduce the levels of lactate after exercise (8).
In contrast, longer-term use of at least 7 days may be beneficial to improving exercise performance (29).
The use of 6 g citrulline for 7 days improves oxygen availability to muscles after moderate to high-intensity exercise (4).
In older men, intake of citrulline also improves exercise performance, however, the effect is moderate (30).
The use of citrulline may not provide immediate benefit in exercise performance. Its use for at least 7 days improved exercise performance. Citrulline malate use may also improve exercise performance.
Can citrulline teat erectile dysfunction?
Citrulline can alleviate symptoms of mild erectile dysfunction.
Nitric oxide is not only a vasodilator, but it is also a neurotransmitter in the penile nonadrenergic noncholinergic nerve fibers.
To date, the most effective way to treat erectile dysfunction is the use of phosphodiesterase type 5 (PDE-5) inhibitors.
Research shows that low levels of arginine and citrulline are produced in individuals with erectile dysfunction, which may exacerbate the symptoms (31).
A placebo control study showed that the use of citrulline 3 g per day for 2 months was effective in reducing erectile dysfunction symptoms without any adverse effects.
It was less effective compared to PDE-5 inhibitors, but it is safer (32).
The use of oral intake of pycnogenol and arginine is also effective in treating mild erectile dysfunction (33).
By improving nitric oxide amounts, citrulline alleviates mild erectile dysfunction. It may present a safer option compared to PDE-5 inhibitors.
How much citrulline to take per day?
The research used various amounts of citrulline to study its effects.
Several studies found blood pressure lowering effects by using d citrulline 6 g per day for at least 6-8 weeks.
For athletic performance, studies used 3 to 8 g of citrulline.
The current minimum dose to see any therapeutic effect is 3 g per day.
Clinically, 10 g per day use may provide benefits, but using more than 10 g per day may not provide any additional benefits (34).
In summary, the use of 3 to 10 g per day of citrulline can provide therapeutic benefits.
Is taking citrulline safe?
Yes, taking citrulline is safe because citrulline is a naturally occurring amino acid found in the body.
Currently, studies in young and elderly show no adverse effects.
Large doses (13 g per day) may cause stomach discomfort and other related gastrointestinal issues (35).
Since citrulline decreases blood pressure, people with low blood pressure should consult their physician before citrulline intake.
You should also consult your doctor if you are:
- Suffering from any medical condition
- Suffering from low blood pressure
- Taking heart medication
- Pregnant or lactating
Citrulline is an important non-essential amino acid. It is found in watermelon but is also available as a citrulline malate supplement
There are several benefits of citrulline. It can lower blood pressure, increase nitric oxide levels, improve physical performance as well as treat low to mild erectile dysfunction.
It is routinely used by bodybuilders and gym-goers to increase exercise performance and Recovery.
As a supplement. Citrulline is safe to consume with no adverse side effects.