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Citrulline Malate is a combination of two potent active ingredients – L-citrulline and Malic acid.
L-citrulline is an amino acid produced by the human body and found in some foods. Watermelons are a well-known natural source of L-citrulline. Malic acid also occurs naturally in the human body. It is a highly effective component that stimulates the aerobic energy production from oxygen.
Citrulline Malate has been used for medicinal purposes in Europe for more than 20 years. Its original use was as an antiasthenic, for treatment of patients with fatigue and muscle weakness.  As the pharmacological action of this amino acid became more well known, research was extended to explore its usefulness for high strength athletes. It wasn’t long before Citrulline Malate was included in many pre-workout shakes and as part of a high exercise diet.
But, the benefits of Citrulline Malate extend beyond the high strength athlete. It offers general health benefits to the cardiovascular system, cleans out wastes after exercise and improves aerobic energy production. It has also been found to improve protein synthesis in aged patients, thus staving off malnutrition. While not as potent as Viagra, it has been known to alleviate male erectile dysfunction.
From its humble beginnings on the fringes of medical care for specialized cases of asthenic, it has now become almost standard use for high strength training. Studies continue to explore its benefits and no doubt its effect on the human body will be better understood over time as even more opportunities come to light.
Benefits and Effects
Improves cardiovascular health
Citrulline Malate increases NO levels in the body. This is the underlying cause of a number of the benefits that Citrulline Malate offers. NO has the effect of relaxing muscle cells, which causes a widening of blood circulation vessels in a process called vasodilation. In terms of the cardiovascular system, the widening of blood vessels lowers resistance to blood flow, which improves blood pressure. It also lowers the stress on the heart to pump the same volume of blood through the body.
Studies on young men without any known health issues were done using the Cold Pressor Test (CPT). The test invokes a constriction of blood vessels due to a cold temperature. It was observed that participants consuming L-Citrulline supplements (available from Citrulline Malate) showed a consistently better blood pressure performance in the CPT than other participants.  Another interesting study focused on a measure of arterial stiffness in a sample group. Once again, those consuming L-Citrulline showed a noticeable improvement, without affecting the blood pressure. 
Researchers have also investigated the benefits of Citrulline Malate in heart failure patients. The right ventricle ejection fraction increased, while the systolic pulmonary artery pressure decreased. 
Reduces ammonia and lactic acid
The increased NO that Citrulline Malate is responsible for has the added benefit of improving blood flow. Higher volume of blood flow through the body means a more efficient removal of waste products like ammonia and lactic acid. This is especially valuable to athletes in training. The buildup of lactate in the body constrains the physical performance of athletes. A study using trained athletes showed that Citrulline Malate has a direct effect on the presence of lactate in the blood after resistance exercises. In addition, the number of repetitions performed by athletes was improved when taking Citrulline Malate.  These results were confirmed by another similar study using lower body resistance exercises. 
A comprehensive test was also performed with female athlete participants. Both upper body and lower body exercises were included in the test regime. Once again athletes consuming a Citrulline Malate dosage showed significant performance improvement. Indications from all these tests in both male and female patients show that Citrulline Malate could be a valuable supplement for strength-based athletes. 
Increases aerobic energy production
The ability to exercise for long periods is related to the body’s aerobic energy production. Citrulline Malate increases the rate of muscle ATP while exercising. Sugar and fats are burned up in muscle cells under the influence of weak amino acids. When this process breaks down, aerobic energy production stops and fatigue sets in. Citrulline Malate helps this process keep going thus improving endurance. 
Improves protein absorption in the aged
Malnutrition among aged people is a medical concern as the body fails to absorb the nutrients and proteins it needs. Studies in rats have shown that supplements of Citrulline play a significant role in alleviating this issue. Citrulline improves the protein metabolism leading to higher protein synthesis and muscle content. Further studies are needed to further evaluate this mechanism of action in humans, but initial signs are promising. 
May improve male erectile dysfunction
Although different studies reach different conclusions on the effectiveness of Citrulline Malate for male erectile dysfunction, some research indicates a positive effect. One study in particular reports that half of the subjects reported an improvement in their erectile hardness. Citrulline Malate may influence the action of enzymes that inhibit the flow of blood to the penis. 
May improve cognitive performance in athletes
Researchers have investigated nootropic stacks that can enhance cognitive and exercise performance. The idea is to enable tournament athletes requiring fast reaction time and endurance to maintain a consistently high level of performance. A selection of Taekwondo athletes participated in three successive fights. Cognitive performance was measured using Taekwondo specific reaction tests. Those athletes taking the BCAA, Arginine and Citrulline stack produced a significantly superior cognitive performance compared to those taking a placebo. 
How it Works
Citrulline Malate has a few different mechanisms of action in the human body.
The most prominent and well-known mechanism is in the metabolic process that produces NO. Citrulline Malate is converted in the kidney into another L-citrulline. From there, enzymes in the liver convert it to another amino acid – L-arginine. It is interesting to note that taking a Citrulline supplement is more effective in raising L-arginine levels than taking L-arginine itself. This is because the body’s absorption of L-arginine is poor. More enzymes convert L-arginine into Nitric Oxide (NO), which is the potent force behind vascular dilation. 
The Malate part of Citrulline Malate works on the Krebs cycle in the body. This cycle is primarily involved in the conversion of oxygen to energy. Malate seems to reduce the effects of excess ammonia that builds up during exercise. It also uses lactic acid to make pyruvate. This means that the waste products generated by exercise are effectively nullified in terms of their limitation on exercise endurance. Aerobic metabolism continues freely, producing more ATP and therefore reducing fatigue. 
Citrulline Malate also increases insulin in the body as well as making more efficient use of amino acids during exercise. Growth hormones also show an increase in the human system after introduction of Citrulline Malate. 
Studies show that an optimum dose of Citrulline Malate for improved exercise performance is about 8 g per day. However, from about 3 g per day effects are already noticeable. There does not seem to be any negative consequences to taking the daily dosage at once or spreading it throughout the day in smaller quantities. 
Because Citrulline is produced naturally in the body, it is not considered toxic to humans. Side effects from Citrulline Malate are very rarely reported.
However, due to the clear effect of Citrulline Malate of relaxing blood vessels and increasing blood flow, this nootropic should not be taken with medication that treats high blood pressure.  When in doubt, always consult a medical practitioner before starting a new regime of supplements.
On the other hand, Citrulline Malate may cause a sudden drop in blood pressure when combined with drugs like Viagra and other PDE-5 inhibitors. 
If you are already taking medication for a heart condition, it is also advisable to check with your doctor before adding Citrulline Malate to your diet. Its pharmacological action on the heart and arteries could put you at risk. 
Pregnant women and nursing mothers are not advised to take Citrulline Malate because there is insufficient research to show whether the product is safe for use in these circumstances.
CoQ10 and Citrulline Malate work well together. Citrulline Malate increases energy and eliminates waste products, while CoQ10 replenishes energy after a workout.
Exercise and strength trainers recommend the use of Citrulline Malate as part of a stack designed to improve training effectiveness and exercise performance. It is especially useful as part of a high-level training regime. A typical stack may look like this :
- Whey protein hydrolysate
- whey protein isolate
- micellar casein
- citrulline malate
A BCAA, Arginine and Citrulline stack has been shown to improve cognitive and exercise performance in tournament athletes.