Journal of Young Investigators
    Undergraduate, Peer-Reviewed Science Journal
Volume Seven
Issue 1, March 2003

Biological & Biomedical Sciences
Effect of a Dietary Supplement on Plasma hGH Following Exercise Challenge

Amy Hellman and Kelli Brummer
University of Nebraska at Kearney

Advisor: Janet E. Steele, Ph.D.
University of Nebraska at Kearney


Human growth hormone (hGH or somatotropin) has numerous anabolic effects on many tissues. It is currently of interest as a potential weight-loss supplement because it acts to decrease adiposity by increasing lipolysis and decreasing glucose uptake in adipose tissue. In addition, hGH also acts to increase lean body mass by decreasing glucose uptake and increasing amino acid uptake and protein synthesis in skeletal muscle tissue, potentially improving athletic performance. The purpose of this study was to examine the effectiveness of a dietary supplement whose manufacturer claims it increases the body's natural production of hGH. Twenty-four young adult subjects participated in the double-blind study. Half of the subjects took the nutritional supplement Growlean 15® for one month, while the remaining subjects received a placebo (gelatin). Body composition was evaluated by skinfold analysis. Blood samples for determination of plasma hGH by enzyme-linked immunosorbent assay were taken before and immediately following a 20-minute exercise session performed at 60% maximal effort. There were no significant differences in body composition between groups or changes in body composition within groups. Plasma hGH levels were significantly elevated in both groups following exercise challenge, but there were no significant differences in plasma hGH between groups either before or after exercise challenge. These results suggest that, following one month's use, this particular dietary supplement does not influence body composition or increase plasma hGH in response to exercise challenge.


Human growth hormone (hGH or somatotropin), a single-chain polypeptide (molecular weight = 22,000 daltons) comprising 191 amino acids and two disulfide bridges, has profound anabolic effects. It is secreted by the anterior pituitary gland following stimulation by growth hormone releasing hormone (GHRH) from the hypothalamus, and its secretion is inhibited by hypothalamic somatostatin. Its general influences on growth and development in numerous body tissues are well known. hGH increases RNA, DNA, and protein synthesis, leading to increases in cell size, cell number, organ size, and organ function. In the liver, hGH acts to increase gluconeogenesis and stimulates the synthesis of a family of peptide hormone intermediaries called somatomedins or insulin-like growth factors. The influence of hGH on the activity of chondrocytes is particularly striking as hGH acts to increase all aspects of chondrocyte metabolism, thereby increasing the linear growth of long bones. In adipose tissue, hGH acts to increase lipolysis and decrease glucose uptake, thereby decreasing adiposity, and in skeletal muscle tissue it acts to decrease glucose uptake and increase amino acid uptake and protein synthesis, thereby increasing lean body mass. Plasma levels of hGH are highest during childhood and puberty and gradually decline throughout adulthood and senescence. Research suggests that hGH supplementation in the elderly may decrease wrinkling of the skin, increase energy levels, increase lean muscle mass, increase emotional stability, and improve memory (Rudman et al 1990; Aleman et al 1999). The effects of hGH on adipose tissue and skeletal muscle tissue have prompted interest into the supplemental use of hGH to reduce body fat and increase lean body mass, and numerous weight loss supplements which claim to work by increasing hGH secretion are currently available. While anabolic steroid use among athletes is recognized, athletes have also been known to take hGH in the hopes that it will boost athletic performance (American Medical Association 1988).

Accurate plasma hGH levels are difficult to obtain because of the pulsatile nature of its secretion due to the pulsatile release of GHRH from the hypothalamus, as well as its rapid clearing from the bloodstream (hGH half-life in plasma hGH is 20-25 minutes). In addition, the secretion of hGH is influenced by many factors. For example, decreases in plasma glucose and/or free fatty acids, associated with fasting, stimulate hGH secretion. Furthermore, hGH secretion is stimulated by stage 4 sleep, exercise and other stressors, and various neurotransmitters, including dopamine, serotonin, acetylcholine, and norepinephrine. Conversely, hGH secretion is inhibited by somatomedins, b-adrenergic agonists, cortisol, obesity, and pregnancy (Hartman et al 1993). hGH also inhibits it own secretion by stimulating the production of somatomedins, which in turn stimulate the synthesis and release of hypothalamic somatostatin. Consequently, several hGH stimulation protocols, such as arginine, clonidine, levodopa, and GHRH stimulation, insulin-induced hypoglycemia, and exercise challenge, have been developed to better assess hGH levels (Laboratory Corporation of America 2001).

The purpose of this study was to examine the effectiveness of an over-the-counter dietary supplement whose manufacturer claims it will help individuals reduce body fat and increase lean body mass by increasing the body's natural production of hGH.

Materials and Methods


Healthy young adult (ages 19-25) volunteers were initially screened by resting blood pressure on two separate occasions during a one-week period. Blood pressure was measured twice from each arm with an aneroid sphygmomanometer and stethoscope using standard auscultatory methods based on criteria recommended by the American Heart Association Postgraduate Education Committee. Volunteers with a mean resting arterial blood pressure above 140/90 mm Hg were not invited to participate in the study. In addition, volunteers who were currently taking any kind of weight loss supplement, suffering from any eating disorder, had cardiovascular disease or a respiratory condition such as asthma, were obese (defined as a body mass index greater than 27.2 for males and 26.9 for females), or for whom exercise was not recommended were not allowed to participate. In addition, female volunteers who were pregnant or suspected they might be pregnant were not allowed to participate in the study. The 24 volunteers (15 females and 9 males, mean age 21.5 + 1.0 years, mean height 68.0 + 2.8 inches, mean weight 164.7 + 28.0 pounds, all values + standard deviation) who were invited to participate in the study received written explanations of the procedures and purposes of the study, and signatures on informed consent documents were obtained from each subject prior to participation in the study. Subjects were asked to maintain the same exercise, nutritional habits, and general activities during the period of their participation in the study. They were also requested not to change diet, stop or start smoking or consuming alcohol, or initiate other major lifestyle changes. If these conditions were not possible to maintain, the subject was to inform the investigators and voluntarily withdraw from the study without fear of prejudice. All protocols were approved prior to the beginning of the study by the Institutional Review Board of the University of Nebraska at Kearney and are in accordance with policy statements of the American College of Sports Medicine.

Supplement and Placebo

This was a double-blind study. Twelve of the subjects received a nutritional supplement (Growlean 15®, Performance Research Laboratories, Culver City, CA) whose manufacturer claims will increase plasma levels of hGH ( According to its manufacturer, each dose (3 capsules) of the supplement contains the following: anterior pituitary peptides, 80 mg; hypothalamus, 20 mg; L-glutamine, 200 mg; L-ornithine, 200 mg; L-arginine, 200 mg; L-pyroglutamate, 200 mg; L-glycine, 500 mg; L-lysine, 200 mg; L-tyrosine, 200 mg; phytosterol, 40 mg; soy phosphatides complex, 80 mg; panax ginseng, 80 mg. The remaining 12 subjects received a placebo (gelatin capsules, 600 mg gelatin per capsule, Rexal Sundown, Inc., Boca Raton, FL). All subjects were instructed to take the product in five-day cycles with two days between cycles for a total of four cycles (26 days). The subjects were to consume three capsules on an empty stomach immediately before bedtime and at least three hours following their last meal of the day.

Body Composition

Body composition was evaluated by using calipers to take skinfold measurements before the study began and after completion of the fourth cycle. Skinfold measurements were taken from the abdominal, pectoral, and thigh regions of the male subjects and from the triceps, thigh, and iliac crest regions of the female subjects. Three measurements were taken from each body region of each subject and the average of the three measurements was used to calculate percent body fat using the equation of Brozek et al (1963).

Plasma Collection and Analysis

The day following completion of the 26-day treatment, baseline plasma hGH was measured by taking a small (<500 ml) sample of blood from the subjects' fingertips. A heparinized Caraway micro blood collecting tube was used to collect the blood, which was then placed in a microfuge tube containing 10 ml EDTA for storage. The subject then participated in a 20-minute exercise session on a stationary bicycle, a stair climber machine, or a treadmill (subject's choice). Subjects exercised at 60% of their maximal effort, which was estimated based on the subject's age (220 - age = theoretical maximum heart rate). A wristwatch-style heart monitor (model 02-1001N, Labron Scientific Corporation, Hauppauge, NY) ensured that the subjects exercised at the appropriate effort level. An additional blood sample (<500 ml) was taken immediately following the exercise period. All samples were kept on ice following collection and then centrifuged at 2500 rpm for 5 minutes to separate the plasma from the formed elements of the blood. The plasma was then stored at -20°C until analysis of hGH by enzyme-linked immunosorbent assay (ELISA) (ICN Pharmaceuticals, Orangeburg, NY, ELISA test kit #07B51102).

Data Analysis

Data were analyzed using a student's t-test and analysis of variance. Statistical significance was ascribed for p<0.05.


Initial percent body fat was 22.9 + 5.9 for the control group and 22.0 + 8.9 for the experimental group. Final percent body fat was 23.8 + 7.4 for the control group and 23.1 + 7.8 for the experimental group. Although percent body fat was slightly elevated in both groups at the end of the study, there were no significant differences in body composition between groups or within groups.

Baseline plasma hGH was 2.7 + 1.2 ng/ml for the control group and 3.1 + 1.4 ng/ml for the experimental group. Following exercise challenge, plasma hGH was 8.1 + 1.8 ng/ml for the control group and 7.4 + 2.2 ng/ml for the experimental group. Although plasma hGH levels were significantly elevated in both groups following exercise challenge, there were no significant differences in plasma hGH between groups either before or immediately following exercise challenge.


The results of this experiment suggest that this particular dietary supplement does not elevate plasma levels of hGH as its manufacturer claims. Plasma levels of hGH have been documented to increase following acute bouts of exercise, but the intensity of the exercise seems to play a significant role. In sedentary and trained women, hGH was shown to increase up to seven-fold in response to acute exercise performed to total exhaustion, but neither group demonstrated an increase in plasma hGH to exercise performed at a submaximal level (Chang et al 1986). In males, plasma hGH has been shown to be significantly elevated after 10 minutes of high intensity exercise (defined as exercise performed at the lactate threshold), whereas no significant change in plasma hGH from resting levels was observed following 10 minutes of low intensity exercise (Felsing et al 1992). Therefore, if a dietary supplement is to increase plasma hGH levels in subjects during an exercise session, the exercise may have to be performed at a relatively high intensity for the supplement to be effective. Our observation that both subject groups had significantly elevated levels of plasma hGH following exercise challenge demonstrates that the exercise session was performed at a high enough intensity to increase hGH secretion. Since there were no differences in plasma hGH levels between groups, however, this suggests that the supplement does not influence the quantity of hGH secreted in response to exercise challenge.

Endurance training, resistance exercise, repeated bouts of exercise, and bed rest also affect hGH secretion. Women who trained for one year either at or above the lactate threshold showed an increase in the pulsatile release of hGH, although the increase was greater in the group that trained at a higher intensity (Weltman et al 1992). Males participating in an acute high-volume resistance exercise protocol had altered pulsatile secretion of hGH during sleep compared to control subjects. Specifically, subjects participating in the exercise had decreased hGH secretion during the first half of sleep but increased hGH secretion during the last half of sleep compared with control subjects (Nindl et al 2001). In response to repeated 30-minute bouts of exercise performed at 70% maximal oxygen consumption, moderately trained males showed a progressive increase in hGH secretion (Kanaley et al 1997). Conversely, short-term bed rest attenuated hGH responses to incremental exercise performed to exhaustion in both trained and sedentary males, and this effect was most pronounced in endurance athletes (Smorawinski et al 2001). Therefore, if a dietary supplement is to increase plasma hGH levels in subjects during an exercise session, the type and frequency of the exercise as well as the subject's general activity level during non-exercising days may influence the effectiveness of the supplement.

Examination of the composition of the supplement and the basic biochemistry of these components may shed some light as to why a significantly different increase in plasma hGH levels was not observed in the experimental group. While the descriptions of some of the ingredients of the supplement, such as "anterior pituitary peptides," "hypothalamus," and "phytosterol," are too vague for their possible physiological influences to be evaluated, the potential effects of other ingredients can be described. For example, it is well known that most amino acids, including glutamine, arginine, glycine, lysine, and tyrosine, are glucogenic. In addition, lysine and tryosine are ketogenic. Therefore, this supplement may influence aerobic respiration and ATP synthesis. The amino acid ornithine is not a building block of proteins but is a component of the urea cycle, where it is a direct precursor of arginine. Normal blood concentration of glutamine is significantly higher than most other amino acids, but this is a reflection of its role as a major transport form of ammonia. Glycine is a precursor of porphyrins, so this supplement could increase heme synthesis, and arginine is a key component of creatine synthesis, so this supplement could influence neuromuscular bioenergetics. Phosphatides are involved in the synthesis of triacylglycerol, so this supplement could influence lipid metabolism. Therefore, it is possible that this supplement could affect overall cell energetics, and the manufacturer does claim that individuals taking this supplement will experience an "increase in energy."

The quantity of ingredients in this supplement may be insufficient to elicit significant changes in hGH secretion or athletic performance. It is well known, for example, that arginine is a potent stimulator of hGH release. The arginine stimulation protocol for analysis of plasma hGH requires the infusion of 500 mg of arginine hydrochloride per kilogram body weight over 30 minutes, with plasma samples for analysis of hGH collected at baseline and every 30 min for 2 hours (Laboratory Corporation of America 2001). Three capsules of this dietary supplement would supply merely 200 mg of arginine per subject per day, well below the level known to stimulate hGH secretion. Because ornithine is a direct precursor of arginine in the urea cycle, it could theoretically increase plasma arginine levels, but a supplement containing 200 mg of ornithine per daily dose could hardly be expected to affect arginine levels enough to increase hGH synthesis. Examination of the quantity of ginseng in the supplement further illustrates the likelihood that the ineffectiveness of the supplement is due to inadequate levels of its active ingredients. Ginseng has been shown to improve exercise performance in human subjects, but the dose necessary to elicit these improvements was greater than 1 g daily (Bucci 2000). Since this particular supplement contains only 80 mg ginseng per dose, it is unlikely that this dose would have any significant affect on athletic performance.

The popularity, effectiveness, and safety of dietary supplements in general must be taken into consideration. Sales of dietary supplements have increased nearly 80% since 1994, with annual sales of more than $14 billion, and it is estimated that 100 million Americans purchase dietary supplements each year (Scally and Freeway 2000; Blendon et al 2001). Despite the rapid growth of the industry, questions remain as to the effectiveness and safety of these supplements since many have not undergone adequate clinical trials (Fillmore et al 1999; Ziesel 1999). For example, two popular supplements, Ultra Burn® and Fat Trapper®, contain substances which have been shown to be potentially harmful (Schardt 1999). One of the active ingredients in Ultra Burn® is hydroxycitric acid, which has been shown in clinical trials to cause testicular atrophy in laboratory animals. Fat Trapper® contains a product made from chitin which binds to fat and substances which are lipid-soluble, not only preventing the absorption of fats from the diet but also preventing the absorption of lipid-soluble nutrients like vitamins D and E. Another popular supplement, Hydroxycut®, contains ephedra, which has been linked to heart attack, stroke, seizure, and psychosis (Haller and Benowitz 2000). The U.S. Food and Drug Administration has received reports of more than 80 deaths linked to the use of ephedra (Smith 2001). While the use of hGH for adults with such conditions as pituitary insufficiency or acquired immune deficiency syndrome has been approved by the U.S. Food and Drug Administration, and preliminary studies indicate hGH has beneficial effects on body composition, serum lipid concentration, bone mineral density, muscle strength, and endurance, the use of natural or synthetic (recombinant) hGH for "normal" individuals has not yet been approved (Vance 1998; Mulligan et al 1999).


The authors would like to thank Dr. Kate Heelan and graduate students Darin Falk and Brian Phillips of the UNK Department of Health, Physical Education, Recreation, and Leisure Studies for their assistance. The authors would also like to thank Dr. Brad Ericson of the UNK Department of Biology for his technical assistance in performing the ELISA procedure. The advice of Dr. Robert Messbarger of Family Practice Associates in Kearney, NE, concerning an accepted protocol for analysis of plasma hGH is appreciated. This work was supported by the UNK Department of Biology and a grant for undergraduate student research presented to Amy Hellman and Kelli Brummer from the UNK Research Services Council.


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Journal of Young Investigators. 2003. Volume Seven.
Copyright © 2003 by Amy Hellman, Kelli Brummer and JYI. All rights reserved.

JYI is supported by: The National Science Foundation, The Burroughs Wellcome Fund, Glaxo Wellcome Inc., Science Magazine, Science's Next Wave, Swarthmore College, Duke University, Georgetown University, and many others.
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