Last Updated on July 31, 2020
L-citrulline is a naturally-occurring amino acid that has many purported health benefits for your heart and blood vessel health.
It is rarely found in the diet but is highly concentrated in watermelon.
In the human body it's primarily located in the liver, where it helps detoxify the body and combines with other amino acids to convert to arginine - an amino acid that raises nitric oxide (NO) levels to enhance blood flow.
Nitric oxide (NO) levels decline with aging as our blood vessels become thicker, larger, stiffer, and less flexible. The heart muscle is affected by aging too, as its electrical system, contractile ability and resilience to stress diminishes.
Why is Nitric Oxide production critical for blood vessel health?
When blood flow increases it places shear stress on the endothelium. Shear stress causes the endothelial cells to release nitric oxide which subsequently diffuses into the smooth muscle cells, causing the blood vessels to dilate (vasodilation). Dilated blood vessels allow more blood to get delivered to areas of low oxygen. It is well known that red blood cells deliver oxygen to the tissues; however, nitric oxide is also bound and released by red blood cells to be delivered to areas of low oxygen.
Low nitric oxygen supply is linked to conditions such as:
- Erectile dysfunction
- Type 2 diabetes
- Vascular insulin resistance
- High blood pressure
- High cholesterol levels
- Alzheimer’s disease
Why Citrulline supplements are more effective than Arginine supplements at increasing Nitric Oxide levels?
Citrulline supplements increase nitric oxide levels more effectively than arginine. Dietary intake of arginine gets absorbed through the gut and enters the liver where it is converted to urea. On the other hand, dietary citrulline is not metabolized in the liver but instead is sent to the kidney. When citrulline enters the kidney it is converted to arginine and then gets released into the circulation.
Results show that citrulline supplementation produced higher spikes in arginine levels and higher retention of arginine than arginine supplementation.
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