Monday, March 10, 2008

Human Growth Hormone: Fact or Fiction?

** UPDATE **
The past months have brought us headline after headline about the use of human growth hormone (HGH) by elite athletes as a way to increase muscular strength. From Roger Clemens and the Mitchell Report to Sylvester Stallone and Rambo, HGH remains a hot topic in the news and on the sports pages. The discussion has focused attention on two key issues. The first is that the use of HGH by athletes is growing. Increased awareness and availability of HGH coupled with lack of a test to identify users makes it reasonable to assume that use is increasing. The second issue is that HGH use creates an uneven playing field. That is, athletes who use HGH are bigger, stronger and have a distinct advantage over those who do not. Buying into this statement is more difficult, given what research as found concerning the effects of HGH on muscle mass and strength. It appears the much of the hype over growth hormone as an ergogenic aid is just that, hype.

Soon after this article was posted, Dr. Hau Liu and colleagues at the Santa Clara Medical Center, Stanford University and the Veterans Affairs System published a systematic review on HGH's effects on muscle mass and athletic performance. They reviewed and analyzed 252 short reports and 56 journal articles that had investigated the effects of HGH administration in healthy subjects. They concluded that"claims regarding the performance-enhancing properties of growth hormone are premature and are not supported by our review of the literature." Also, HGH "does not appear to improve strength and may worsen exercise capacity." The article is set to appear in the May issue of the Annals of Internal Medicine.

What is HGH? Growth hormone, also known a somatotrophin, is secreted by the anterior pituitary gland, located at the baseof the brain. HGH is known to have a number of anabolic effects. That is, it stimulates growth of many tissues, particularly bone, connective tissue and muscle. Apart from sleep, the most potent stimulator of HGH release is exercise. The amount of HGH released varies with age. The highest levels are observed in adolescents and the lowest in the elderly.

What are the positive effects of HGH? From a medical perspective, HGH treatments have targeted three groups of patients. There is little doubt that HGH supplements can be beneficial in restoring growth in HGH deficient, short stature children. In true HGH deficiency, treatment results in increased growth rate and final height. However in idiopathic short stature children, children who are short with normal levels of HGH, administration accelerates growth to some extent but does not affect final height. Thus, only when HGH is deficient is supplementation effective. Second group is the elderly. Because HGH levels decline with age, investigators considered that supplementation would restore the loss of muscle mass that accompanies aging. Early results were promising as HGH increased muscle mass and strength in older men. However, more recent studies have been inconsistent and there is no clear consensus as to HGH’s effects on the elderly. Finally, HGH treatments are being targeted towards patients with various muscle-wasting diseases. These including cancer, HIV/AIDS and severely burned patients. At this point results are promising but not conclusive.

On the downside, HGH supplementation has a number of adverse side effects. It can affect both fat and glucose metabolism by stimulating lipolysis (the breakdown if fat stores). This, in turn, inhibits glucose uptake by muscle and leads to decreases glycogen storage. In addition, HGH increases insulin resistance in muscle and other tissues leading to hyperglycemia (this can be viewed as a precondition of diabetes). In terms of performance, reduced muscle glycogen can make the athlete more susceptible to fatigue (see article on Nutritional Strategies). Other potentially harmful side effects include water retention, carpal tunnel syndrome, hypertension and joint pain.

What about athletes and performance? For most athletes, HGH supplements are used in hope of gaining muscle mass or increasing height. However, the overwhelming consensus in the scientific literature is that HGH supplementation in healthy athletes has no effect on muscle mass, muscle performance, growth or stature. The vast majority of research indicates that neither short-term nor long term supplementation provides benefits beyond those earned through training and diet. In fact, the effects on fat and glucose metabolism can adversely affect performance in some sports such as soccer.

Some HGH abusers inject excessive amounts of HGH, dosages that are considered supratheraputic, beyond what would be prescribed by a physician. One might argue that researchers have not studied the effects of high HGH dosages that might be taken by athletes. However, investigators have used treatments that cause large increases in both HGH and insulin-like growth factor 1 (IGF-1, another anabolic hormone) but no anabolic effect on muscle. A further argument against the effect of supratheraputic dosages to induce hypertrophy comes from patients with the condition of acromegaly. In these individuals, excessive amounts of HGH are produced by the anterior pituitary gland. Yet they do not show abnormal increases in muscle mass or strength. In fact, based on their height, muscle size is relatively small compared to normal healthy individuals. Further many of these patients show muscles that are myopathic (i.e. dysfunctional). Thus is seems very unlikely that even excessive HGH supplement us in athletes would cause muscle hypertrophy.

At present, the bottom line is that there are no credible research studies showing beneficial effects of HGH on muscle mass, strength or athletic performance. Nor is there any evidence to suggest that HGH supplementation will increase the stature of an otherwise healthy child, adolescent or adult athlete.

Why all the interest and hype surrounding HGH supplementation? Why are athletes willing to put their health and careers at risk for a compound that does not work? There are probably two major reasons. First, coaches, athletes and especially supplement companies are often quick to generalize the effects observed in one group of individuals to another. The early results showing that HGH increased mass and strength in elderly men were hastily interpreted to mean that healthy athletes would benefit as well. The drive to find the edge needed to win leads some to “buy into” the positive effects shown in a single study while ignoring the negative results of others. Second, the press as well as anti-doping agencies and even congress have fueled interest in HGH as an ergogenic aid. Many athletes make the assumption that if a treatment is banned by an organization such as the International Olympic Committee, it must be effective. In the case of HGH, the myth of its effectiveness is perpetuated by the agencies that seek to eliminate its use.

Taken as a whole, the overwhelming body of research evidence indicates that in healthy athletes, HGH does not improve muscle mass, strength, athletic performance or stature. Abuse, however, can lead to the development of serious, life-threatening complications. As for high profile athletes such as Roger Clemens, it is quite sad to see a career be so damaged by the use of a performance enhancing supplement that probably had no effect on his pitching performance. Coaches and athletes should be aware that the risks of HGH supplements are great while the benefits are few.

Further Reading:

Calfee RC, Fadale P (2006) Popular ergogenic drugs and supplements in young athletes. Pediatrics, 3:e577-e589.

Rennie MJ (2003) Claims for the anabolic effects of growth hormone: A case of the Emperor's new clothes. British Journals of Sports Medicine, 37:100-105.

Tokish JM, Kocher MS, Hawkins RJ (2004) Ergogenic aids: A review of basic science, performance, side effects and status in sports. American Journal of Sports Medicine, 32:1543-1553.