Growth Hormone: Amino Acids as GH Secretagogues – A Review of the Literature
By Kimberly Pryor and Ward Dean, MD
Growth hormone is released by the pituitary gland in the brain. GH is responsible for enhancing muscle growth, burning fat and maintaining the immune system. Many scientists have linked the changes seen with aging—loss of lean body mass, thinning of the skin and an increase in adipose (fat) tissue—to the decline in growth hormone that begins in the human body by the age of 30 (Fig. 1,).
Growth hormone is a concern of many athletes and life-extension enthusiasts, who commonly use amino acid supplements to boost levels of this important hormone. Anecdotal evidence is plentiful that amino acid supplements can offer anabolic effects consistent with growth hormone release. But the question remaining is whether research supports the wide-spread belief that amino acid supplements really do act as growth hormone secretagogues.
Intravenous administration of some amino acids is known to result in a significant growth-hormone release. For example, the 52% rise in serum arginine that occurs after low dose, intravenous arginine infusion is associated with a significant rise in serum growth hormone levels. In fact, clinicians routinely use an arginine infusion test to determine the responsiveness of the pituitary to releasing growth hormone in humans.1-2 Intravenous ornithine also increases growth hormone release in humans, producing a five-fold increase in serum growth hormone in 45 minutes.3
Life extension pioneers Durk Pearson and Sandy Shaw, in their popular book Life Extension: A Practical Scientific Approach, advocated the use of amino acids to boost growth hormone production, particularly ornithine and arginine, and the prescription drug and amino acid, L-Dopa (Fig. 2). It was clear that Pearson and Shaw’s protocol, including ornithine and arginine, did indeed appear to offer benefits. Pearson and Shaw state, L-arginine/L-ornithine cause the release of growth hormone by different mechanisms, so they are even more effective when taken together. However, their book does not go into detail nor describe any examples of growth-hormone-releasing studies performed on either of these two amino acids.4
Given the fact that scientists have presented us with a head-turning volley of contradictory evidence, is Pearson and Shaws unwavering faith in amino acids as growth-hormone releasers justified? An interpretation of the studies relating to amino acids as growth hormone secretagogues shows that, despite the mixed results, there are plenty of reasons to include amino acids in a supplement regimen.
Ornithine
Ornithine is derived from the amino acid arginine. High doses of oral ornithine have successfully raised growth hormone levels in some studies. Bucci, et al, investigated the effect of 40, 100 and 170 mg/kg of oral L-ornithine HCl on 12 bodybuilders. Twenty-five percent of the subjects experienced significant increases in serum growth hormone levels at the two lower doses, while half the subjects showed an increase in growth hormone at the highest dose. Growth hormone rose, in some cases, up to four times the baseline level.5
Unfortunately, the highest dose used to increase growth hormone also caused osmotic diarrhea in the males tested, a side effect not seen in the three females who consumed high ornithine doses. The females also experienced a rise in GH after each dose, leading the researchers to conclude, Oral ornithine should be studied in more detail in female strength athletes.
Arginine
The ability of oral arginine to raise growth hormone has been investigated in numerous studies with conflicting results. For example, in one study, subjects given 6 grams of oral arginine experienced a 100% increase in plasma levels of arginine without any growth hormone release.6 Other researchers administered oral arginine to 12 young and 5 elderly non-obese adults, all of whom had a body mass index (BMI) less than 30. The subjects participated in three trials: resistive weight-lifting exercise with no placebo; 5 grams of oral L-arginine only; and 5 grams of arginine supplementation prior to exercise.
When arginine was consumed at rest, it did not significantly raise GH levels, compared with baseline values, in either the young or the old subjects. In fact, GH levels in those consuming arginine at rest were significantly lower than during the exercise-only trial. Consuming arginine before exercise did not significantly raise the GH concentrations in either the old or the young subjects, compared to exercise only. Surprisingly, the amount of GH secreted in the exercise-plus-arginine trial was 20% less than during exercise only in the young subjects, indicating arginine may actually blunt growth hormone production, particularly in the young.7
Other researchers drew the same conclusion in a study of 16 young men during an acute episode of resistive weight lifting. After 3 grams of oral arginine and lysine, the subjects experienced a peak GH response to exercise approximately 15% lower than during exercise without supplementation.8 One group of researchers, after reviewing the evidence, wrote, These results suggest that oral arginine, unlike intravenously infused arginine, does not appear to be an effective means of enhancing GH secretion.7
Researchers suspect that arginine may only act as a growth hormone secretagogue at night, rather than prior to exercise or during non-exercise daytime conditions. When researchers administered 250 mg/kg/day of oral arginine aspartate to five healthy subjects aged 20 to 35 for seven days, the rise in GH that occurred during slow wave sleep was approximately 60% higher in the subjects after arginine aspartate administration than in the control period. These same results were not obtained with a lower dose of 100 mg/kg/day.9
Another group of researchers achieved promising results when treating 12 normal adults with one large, 37.5-gram dose of arginine aspartate, administered orally. The treatment caused a small but significant release of serum growth hormone in these subjects.10
Arginine and Ornithine
When administered together, arginine and ornithine do appear to offer anabolic benefits. These benefits appear to be caused by growth hormone release, but this remains unproven. In a double-blind study of 22 adult males participating in a 5-week progressive strength-training program, half the subjects orally consumed a combination of 2 grams of L-arginine and 1 gram of L-ornithine; the other half consumed a placebo. Following a short-term strength program using progressively higher intensities, subjects taking the arginine-ornithine combination scored significantly higher in total strength and lean body mass and excreted less urinary hydroxyproline (an amino acid found in collagen, the excretion of which is a marker of catabolism) than subjects on placebos. In reviewing the study, one group of researchers wrote, It was concluded that arginine and ornithine taken in prescribed doses can, in conjunction with a high-intensity, strength-training program, increase total strength and lean body mass in a relatively short time.
The researchers suggested that the lower hydroxyproline levels were an indication that arginine and ornithine aided in recovery from chronic stress by alleviating tissue breakdown. The reviewers hypothesized that these changes were due to increases in growth hormone release, although GH was not measured.11-12
Ornithine-alpha-ketoglutarate (OKG)
Ornithine alpha-ketoglutarate (OKG) is a salt formed of two molecules of ornithine and one molecule of alpha-ketoglutarate. OKG is a promising anti-catabolic agent that promotes wound healing and protein synthesis. Researchers have hypothesized that OKG fulfills these functions by encouraging the secretion of insulin and human growth hormone, and by upregulating glutamine and arginine production. When fed enterally to trauma patients, OKG significantly increased both IGF-1 and growth hormone levels.13-17
Although few, if any, oral studies exist on OKGs ability to release growth hormone in normal subjects, studies do show that in healthy subjects OKG does increase tissue levels of glutamine and arginine, which are regulators of protein synthesis. In fact, animal studies show that ornithine alpha-ketoglutarate (OKG) generates more glutamine in the systemic circulation than glutamine itself when these substances are given orally.18-19 Oral glutamine has been shown to release growth hormone in some studies.20
Arginine Pyroglutamate and Lysine
Arginine and lysine may work synergistically to release growth hormone. In a study of 15 healthy male subjects, separate consumption of arginine pyroglutamate or lysine as single nutrients did not significantly increase growth hormone compared to baseline. In another study of normal young males, oral administration of 1,200 mg of L-lysine did not raise serum growth hormone levels.21
Studies indicate, however, that these two amino acids can work together to instigate the release of growth hormone. In 15 healthy male subjects aged 15 to 20 years old, 1200 milligrams of arginine pyroglutamate combined with L-lysine hydrochloride significantly elevated biologically active growth hormone from two to eight times the baseline value at 30 to 120 minutes after consuming the amino acids.21
Another study indicated arginine and lysine may act to increase growth hormone—but only under specific conditions. Sixteen men randomly completed four trials. Trial A consisted of a performance of a single bout of resistance exercise preceded by placebo ingestion (vitamin C). Trial B involved ingestion of 1,500 mg L-arginine and 1,500 mg L-lysine, imwww.ely followed by exercise as in Trial A. In Trial C, subjects consumed arginine and lysine as in Trial B, but with no exercise. In Trial D, subjects consumed a placebo and did not engage in exercise. There was no difference in growth hormone concentrations between the placebo-supplemented subjects and the amino acid-treated subjects. However, in Trial C, during resting conditions, growth hormone was significantly elevated 60 minutes after consumption of arginine and lysine compared with the placebo trial. The researchers concluded that ingestion of 1,500 mg arginine and 1,500 mg lysine before resistance exercise did not alter exercise-induced changes in GH in young men. When the same amino acid mixture is ingested under resting conditions, however, acute GH secretion is increased.22
Unfortunately, not all studies investigating the use of arginine and lysine have resulted in positive findings. One study investigated whether oral arginine/lysine could be used to increase basal IGF-I and GH levels in non-obese elderly men to values similar to those of untreated young men. Researchers gave two groups of 8 healthy elderly men either 1.5 grams of arginine plus 1.5 grams of lysine or a placebo twice daily for 14 days. The researchers also administered the amino acid combination to young men during the same time period and measured GH and IGF-1 levels. The researchers found that arginine and lysine administration did not significantly alter basal or sleep-related GH levels or serum IGF-I, either in the elderly or young subjects. Our data suggest that oral arginine/lysine is not a practical means of chronically enhancing GH secretion in old men, the researchers reported.23 Another group of researchers suggested the lack of GH release in this study may be due to the low doses used.7
Glycine
Glycine is a nonessential amino acid contained in gelatin protein and is an important component of collagen. Although much of the early research revolved around glycines ability to increase strength in athletes, more recent studies have documented that oral glycine can indeed raise growth hormone levels in humans. In fact, researchers have hypothesized that the reason glycine has been found to increase muscle strength in many studies, (with females experiencing a 22% increase and men a 32% increase in cycle ergometry workloads after ingestion of 5 to 12 grams of glycine daily) may be the result of its growth-hormone-boosting capabilities.24
One study clearly illustrated glycines ability to act as a GH secretagogue. When 19 normal, non-obese subjects consumed 6.75 grams of glycine orally, growth hormone levels significantly increased for 3 hours, reaching a maximum of 3 to 4 times that of baseline at 2 hours. Interestingly, the only group of subjects not deriving a growth-hormone-boosting benefit from glycine was non-obese diabetics. According to the researchers, glycine is one of the stimulatory agents inducing the pituitary gland to secrete hGH.25
On the other hand, another study of eight men revealed that six or twelve grams of glycine daily for 10 weeks could increase urine creatine levels, but did not improve grip strength.26 These same disappointing results were upheld in a double-blind, crossover study of 33 football players given a placebo or 5 grams of glycine daily. After consuming glycine for 21 days, the subjects did not experience any noticeable benefit to work output.27
After reviewing the above studies, one group of researchers hypothesized that the reason glycine showed no effect in the later trials is because glycine enhances growth hormone levels already produced during a whole-body resistance training program and during anaerobic or intermittent exercise. In subjects performing endurance exercise where growth hormone release is low, glycine would not show any benefit because this amino acid only enhances effects of growth hormone already produced. The researchers concluded, Acute ingestion of large p.o. doses of glycine appears to stimulate release of growth hormone and increase creatine synthesis rates. Both of these attributes are desirable for persons undergoing progressive weight training.28
More recent research lends support to the above hypothesis. In a randomized, double-blind, crossover study published in December 2000, 13 human subjects were given a supplement consisting of glycine and an L-arginine salt or a placebo over 23 days. Treatment with arginine and glycine increased the subjects mean resistance to fatigue up to 28% over the controls during acute exhaustive high-intensity anaerobic isokinetic exercise. The subjects taking glycine and arginine also experienced an overall gain in total muscle work of 10.5% more than controls.29
Glutamine
Glutamine is the most abundant amino acid in human muscle and plasma, directly regulating both the production and wearing-down of protein and immune cell activity.30-31 When 9 healthy subjects consumed two grams of oral glutamine 45 minutes after a light breakfast, 8 of the 9 subjects experienced elevated plasma growth hormone within 90 minutes. These findings demonstrate, the study authors wrote, that a surprisingly small oral glutamine load is capable of elevating…plasma growth hormone.32
In the small intestine, glutamine is converted into citruline, which in turn triggers the synthesis of arginine, an amino acid shown to release growth hormone in some studies. Moreover, glutamine is converted into glutamate, which can directly enhance growth hormone secretion.
GABA
Gamma-aminobutyric acid (GABA) is the brains major inhibitory neurotransmitter. Studies have shown it is responsible for both the rise of growth hormone (when at rest) or the inhibition of growth hormone (when exercising).33-35 Oral GABA supplementation has increased growth hormone levels in humans. In one study, a single oral dose of 5 grams of gamma aminobutyric acid administered to 19 subjects significantly elevated plasma growth hormone levels compared to placebo-treated controls.36
Additional Benefits
Each of the amino acids discussed here offers a number of other benefits beyond their potential role in growth hormone release. For example, glutamine shifts the fuel for muscle from glucose to fatty acids and accelerates fat burning. Glutamine is also a precursor for the antioxidant glutathione, which protects the liver. Supplemental glutamine has shielded the body from stress by deflecting cortisol damage, and has prevented the muscle wasting associated with cortisol treatments.37-39 Another example is ornithine, which is an important constituent of the urea cycle and, together with arginine, an important immunity-enhancing nutrient. Ornithine may help reduce elevated ammonia levels seen after exercise, a benefit that can result in reduced fatigue.40
Given the number of benefits amino acids produce independently of growth hormone release, whether or not they act as growth hormone secretagogues may not be the most important consideration in adding them to a supplementation regimen.
| Amino Acids | Study Results |
| Intravenous Ornithine | Produces a five-fold increase in serum growth hormone in humans. |
| Ornithine | Increased serum growth hormone in bodybuilders, up to four times the baseline level. |
| Arginine | 250 mg/kg/day of oral arginine aspartate given to five healthy subjects for seven days caused a 60% rise in GH during slow wave sleep compared to the control period. |
| Arginine and Ornithine | In a double-blind study, adult males participating in a 5-week progressive strength-training program who consumed 2 grams of L-arginine and 1 gram of L-ornithine experienced significantly higher total strength and lean body mass scores and excreted less urinary hydroxyproline than placebo-treated subjects. |
| Ornithine Alpha-ketoglutarate (OKG) | Significantly increased IGF-1 and growth hormone levels in trauma patients. In healthy subject, OKG increased tissue levels of growth-hormone-releasing glutamine. |
| Arginine and lysine | 1200 milligrams of arginine pyroglutamate combined with L-lysine hydrochloride significantly elevated biologically active growth hormone from two to eight times the baseline value in 15 healthy male subjects aged 15 to 20 years old. |
| Arginine and lysine | 1,500 mg arginine and 1,500 mg lysine increased GH in young men only during resting conditions. |
| Glycine | In 19 normal, non-obese subjects, 6.75 grams of glycine increased growth hormone levels up to 300 to 400 percent that of baseline. |
| Glycine and L-arginine | Increased the subjects mean resistance to fatigue up to 28% over the controls during acute exhaustive high-intensity anaerobic isokinetic exercise and produced an overall gain in total muscle work of 10.5% more than controls. |
| Gamma Aminobutyric Acid (GABA) | A single oral dose of 5 grams of GABA administered to 19 subjects significantly elevated plasma growth hormone levels compared to placebo-treated controls. |
| Glutamine | Two grams of oral glutamine resulted in elevated plasma growth hormone in 8 of 9 subjects tested. |
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