Citrulline and L-Citrulline

Citrulline is, like arginine, a semi-essential amino acid.  It can be produced in the body as part of the urea cycle.  Interestingly, citrulline results from the break down of arginine, which, if you have been following this blog, is a key amino acid in the creation of nitric oxide.  So one might not think that having more citrulline would lead to more arginine, but it does.   Nitric oxide is an essential molecule which signals the blood vessels to relax, increasing the flow of blood, oxygen and nutrients to our muscles and organs.  Citrulline is also a marker amino acid, meaning that doctors can look at the amount of citrulline in the blood and intestines to determine functionality as well as predict certain conditions like rheumatoid arthritis.

Citrulline, most likely by virtue of its role in arginine and nitric oxide production, has been found to help maintain the correct nitrogen levels in the body.  It also helps strengthen the immune system and aids in the creation of human growth hormone, insulin and creatine.  Athletes and bodybuilders will immediately recognize these benefits!  Citrulline malate is sold as a nutritional supplement, usually with arginine, and has been shown to reduce muscular fatigue in at least one clinical trial at the University of Medicine in Cordoba, Spain .  Citrulline malate has also been used in Europe for the treatment of dementia.

These benefits are most likely related to the creation and balance of nitric oxide.  Nitric oxide has been called the miracle molecule for a good reason.  It cannot be overstated that nitric oxide’s primary benefit of signalling the blood vessels to relax and expand has profound effects on overall health.  Besides helping to control blood pressure and improve circulation, nitric oxide has positive benefits on everything from mental acuity and hair growth to wound healing and muscle building.  The increase of blood flow caused by properly functioning blood vessels is critical to delivering oxygen and nutrients to the cells as well as removing waste products.

Citrulline can be found in citrus foods like watermelon (the rind), cantaloupe and cucumbers.  It is also found in milk, fish, eggs, nuts and red meat.  In short, foods rich in protein also have citrulline in them.  Walnuts also appear to be a good source.   Studies have shown that 1 – 2 grams of citrulline per day can lead to an increase of 22% in serum arginine levels, and hence more nitric oxide.   Like any supplement, it is important to follow dosing instructions.  While it does not appear that the potential side effects of too much citrulline extend beyond stomach ache, headache, dry mouth and fatigue, it is important that you consult with your doctor before adding this supplement to your diet.

You can find citrulline supplements as well as other nitric oxide supplements at or  I personally have purchased products from both of these stores and have been impressed with their customer service and professionalism.