Visit any bodybuilding forum on the web and you’ll see mention of ornithine and its athletic performance-enhancing and muscle-building benefits. This amino acid (also called: L-Ornithine, L-Ornithine HCl, L-Ornithine Hydrochloride, L-5-aminorvaline, L-2,5-diaminovaleric acid, and Ornithine HCl) is frequently promoted as a dietary supplement for stimulating muscle growth. But is an ornithine supplement the best amino acid supplement for muscle building?
5 Top Uses for Ornithine Supplements
While much of the excitement about ornithine has to do with its impact on muscle mass and athletic performance, scientists have found that this potent amino acid can affect your health in other ways as well.
Here's further information on five of the top reasons people try ornithine supplementation:
- Anti-fatigue effects: Some evidence indicates that ornithine helps flush fatigue-inducing metabolites from your muscles and can relieve fatigue related to excess ammonia in the blood (common with chronic stress).
- Increased muscle mass: Studies show that ornithine supplementation can positively influence factors that stimulate the growth of muscle tissue, like testosterone and growth hormone levels.
- Boosted athletic performance: Because of its role in the urea cycle, ornithine can increase your capacity for physical exertion, allowing you to push yourself harder, for longer.
- Enhanced wound healing: Research shows that ornithine supplementation can substantially improve wound healing, largely due to the way ornithine influences collagen synthesis.
- Strengthened immune function: At least one study (which looked specifically at the use of ornithine alpha-ketoglutarate) has found that ornithine can improve your immune function.
How the Body Uses Ornithine
In order to understand the mechanics of L-ornithine supplementation, it's important to have a grasp on the basics of how your body uses amino acids.
Amino acids, in technical terms, are simple organic compounds that link together to form protein. Our bodies need an adequate supply of amino acids to build muscle tissue and perform other vital functions. Because amino acids—including L-ornithine—are so essential to our overall health and well-being, they've earned the moniker: the building blocks of life.
A quick note about why you'll sometimes see amino acids like ornithine referred to interchangeably as “L-ornithine” and "ornithine." Amino acids can be in either a D configuration (like D-aspartic acid) or L configuration (like L-aspartate). However, since there really isn’t a “D-ornithine” in supplements, it's common to see both terms used synonymously.
When we talk about amino acids, we tend to focus on the role they play in protein metabolism. But certain amino acids carry out different functions that are not directly linked to the synthesis or production of protein. These acids are categorized as non-proteinogenic amino acids or NPAAs.
Neither the proteins we eat nor the proteins our bodies make contain ornithine. Rather, ornithine functions in the liver as part of the urea cycle. In fact, the urea cycle is often called the ornithine cycle because ornithine is such an important component.
Understanding the Urea Cycle
The urea cycle is a biochemical reaction that converts ammonia to urea that the body can then excrete. This is an absolutely crucial detoxification process since excess ammonia, a waste product generated from cellular metabolism, can be toxic when blood concentration levels rise too high.
The urea cycle has four phases: 1) your liver produces urea, 2) your liver releases the urea into your bloodstream, 3) the urea travels to your kidneys, 4) your kidneys excrete the urea in your urine.
As part of the urea cycle, ornithine combines with ammonia to form the amino acid L-citrulline, or more simply, citrulline. Citrulline then combines with another ammonia molecule to form the amino acid L-arginine, which is more commonly referred to as (you guessed it) just plain arginine. From here, arginine is converted to ornithine, with urea as a byproduct—and we’re back to where the cycle started. Ornithine to citrulline to arginine to ornithine, and so on.
So, the urea cycle converts ammonia to nontoxic urea for excretion by the kidneys without disrupting amounts of the essential components: arginine, ornithine, and citrulline. In almost all circumstances other than liver failure, the cycle functions adequately to produce urea and prevent excess ammonia from entering the bloodstream. None of the amino acids involved in the urea cycle are essential amino acids, which must be taken in from the food you eat or from dietary supplements. Under normal conditions, the body produces sufficient amounts of these nonessential amino acids to effectively keep plasma ammonia levels in check and produce urea for elimination.
Why You Should Care About Your Nitric Oxide Levels
The idea behind ornithine supplementation (and prior to that, arginine supplementation), is that it can increase blood levels of nitric oxide, a desirable outcome for several reasons.
During the urea cycle, a small percent of arginine is not converted to ornithine but rather is converted to citrulline. Nitric oxide (NO) is the byproduct of this arginine to citrulline conversion. Testing has revealed that nitric oxide helps to regulate how much blood can pass through your blood vessels. When nitric oxide levels increase, the diameter of your blood vessels expands, a process known as vasodilation. Maximizing vasodilation during exercise can be highly beneficial since you want as much blood flowing to your muscle tissue as possible in order to bring in oxygen and nutrients and clear out waste products.
Nitric oxide also supports healthy sexual function in men.
Methods for Increasing Nitric Oxide Levels
As scientists began to appreciate the physiological importance of nitric oxide, they devised different approaches to promote its production.
1. Arginine Supplementation
One of the first methods they tried was arginine supplements, which have been used since the 1950s. In the early days, arginine supplements were considered to have nutraceutical properties, as they seemed to have more potent effects than would have been expected, but the precise mechanisms were not understood.
Subsequent studies showed that the benefit of arginine supplementation was due at least in part to the increased production of NO. Arginine was also found to have a direct stimulatory effect on muscle protein production by activating a key molecular factor inside the cell (mTOR). Finally, in large doses arginine was discovered to stimulate the release of growth hormone.
There are, however, two considerable problems with arginine supplementation. The first has to do with the cellular metabolism of arginine. After L-arginine is absorbed from the intestine it must pass through the liver before reaching the blood in the rest of the body. However, your liver cells very effectively take up and metabolize orally ingested arginine. As a result, consuming oral L-arginine has only a small effect on blood levels of arginine.
The second problem, which is related to the first, is that in order to elevate blood levels of arginine to the desired extent, you have to take doses that are so high they cause digestive distress in most people. Studies show that doses of arginine at 10 grams and higher can cause diarrhea as well as other unpleasant side effects.
2. Ornithine Supplementation
Given the problems with using dietary supplements of arginine, scientists started to explore alternate options for raising arginine levels in the blood with the ultimate goal of increasing nitric oxide production.
We’ve already seen how ornithine, citrulline, and arginine convert from one to the other via the urea cycle. Both amino acids are possible alternative approaches to arginine supplementation. The idea behind ornithine supplementation is to increase arginine by conversion in the urea cycle.
Research indicates that oral L-ornithine supplementation can have an anti-fatigue effect while improving measures of athletic performance including speed, strength, and power.
A study published in the Journal of Sports Medicine and Physical Fitness found that ornithine supplementation increased lean muscle mass as well as power output for weight lifters.
Separate findings from a study done with bodybuilders demonstrated that ornithine can increase growth hormone levels. Low-dose ornithine supplementation had no effect, but the highest dose (170 milligrams of ornithine hydrochloride) increased growth hormone concentrations to 318% above baseline. As with arginine, high doses of ornithine frequently cause digestive side effects.
The effects of ornithine on growth hormone appear to be short-lived. The desirable effects of raising growth hormone levels, such as increased lean muscle mass gains and fat loss, occur when you sustain elevated levels. This makes ornithine supplementation an ineffective method for pursuing those goals.
3. Citrulline Supplementation
Another reason taking an ornithine supplement may not be the most logical route to achieving goals like improved endurance and increased muscle mass is that the ornithine you take is converted to citrulline, which is then converted to arginine. So, ornithine is two metabolic steps away from arginine.
Keep in mind too that if your primary reason for trying arginine supplementation or ornithine supplementation is to build muscle and maximize your athletic performance, you need to increase nitric oxide production and stimulate muscle protein synthesis and muscle growth.
Citrulline is the optimal nutritional supplement to achieve this. Unlike arginine, the liver lets most of the absorbed citrulline pass through. Citrulline is largely converted to arginine in the kidneys, which release the arginine into the blood for circulation to the rest of the body, including muscle tissue. This explains the surprising fact that the blood level of arginine increases much more after consumption of citrulline than after the same amount of arginine.
The second aspect of citrulline that makes it a great way to increase arginine concentration is that citrulline consumption rarely causes gastric distress.
All in all, it appears that supplementing with citrulline is the most effective way to increase blood levels of arginine as well as ornithine, elevate production of nitric oxide, and reap the benefits.