What is Growth Hormone?


  1. What is Growth Hormone?
  2. Effects of Growth Hormone
  3. Growth Hormone Disorders & Therapy

What is Growth Hormone?

Consciously, or not, what most athletes are striving for by training is to elevate their anabolic (growth-promoting) hormone levels. Growth hormone, also known as somatotropin, is our most important anabolic hormone possessing both developmental and metabolic properties.

Developmental: During our initial decades of life growth hormone is principally responsible for the growth of bones and muscles. Beyond 30 years of age, however, our growth hormone levels begin to decline and is associated with a steadily loss of muscle mass and bone reabsorption.

Metabolic: Another major role of growth hormone is to regulate which substrates are used for energy production. Growth hormone mobilizes lipids (fats) for energy usage. Amino acids (proteins), on the other hand, are spared from being used as energy substrates under the influence of growth hormone. Growth hormone thus keeps our fat reserves at a healthy minimum and our muscle content high. In other words, growth hormone effectively promotes the development of lean (fat free) muscle. In fact, the “pot-belly” that appears in most males during their 30′s is a function of this age-related reduction in growth hormone.

Anti-Aging: There is currently a lot of excitment about the possibility of growth hormone replacement as an anti-aging therapy. Athletes are also looking for ways to increase their growth hormones levels in order to build more muscle and reduce body fat.

Regulation & Regulators of Growth Hormone

Central Nervous System Release

The Hypothalamus is a part of the brain that serves to integrate and respond to information it receives from the rest of the body. In particular, the hypothalamus exerts control over the secretions of the Anterior Pituitary, a small gland located at the base of our brains. The pituitary is also commonly referred to as the Master Gland, which should give you some idea of its importance. Therefore, the hypothalamus, via its direct control over the anterior pituitary, indirectly governs the body’s growth and metabolic processes.

Rather than a steady stream, however, growth hormone is released from the anterior pituitary in spurts due to the competing actions of stimulatory and inhibitory factors originating from the hypothalamus.

Hypothalamic Factors

Stimulatory: Growth Hormone Releasing Hormone, or GHRH, produced by the hypothalamus stimulates the anterior pituitary to secret growth hormone.

Inhibitory: Somatostatin antagonizes the release of growth hormone from the anterior pituitary. Like GHRH, somatostatin is produced in the hypothalamus from where it acts on the anterior pituitary.

Regulatory Feedback

Growth hormone is not wasted. Once secreted into the blood stream growth hormone inhibits its further release from the anterior pituitary (and hypothalamus). The net result is that growth hormone release is favored when its levels are low and is inhibited when it is present in adequate amounts. This is a classical case of negative feedback and prevents the overproduction of growth hormone; a biologically economic measure.

Regulators of Release

Age-Dependence: Growth hormone levels are highest during puberty. Accordingly, this is when we are growing the most rapidly. After about 30 years of age our growth hormone levels begin to decline at a rate of about 14% per decade.

Translating this into practical terms…, if we were producing 500 micrograms of growth hormone per day at 20 years, we would be producing only about 25 micrograms per day by the time we reach 80!

It is now commonly thought that an increase in circulating somatostatin underlies this age-related reduction in growth hormone production.

Sleep-Dependence: After an hour, or so, of initiating sleep we enter into a mode of deep sleep known as Slow Wave Sleep, or SWS. SWS occurs only during the initial hours of sleep and appears to be inhibited as the night progresses.

We build muscle while we sleep… Growth hormone is principally released from the anterior pituitary during moments of SSW. Therefore, anything that interferes with our SSW will likewise interfere with the release of growth hormone. Alcohol, in particular, interrupts SSW and consequently will also inhibit the release of growth hormone from the anterior pituitary.

Note: I would discourage young athletes who are serious about gaining muscle mass, from consuming alcohol, at least immediately before bed or after exercise (see below).

Exercise-Dependence: Growth hormone is also released following exercise. This aspect of growth hormone release is extremely important for muscle recovery following exercise. Excessive exercise, however, shocks our system into producing somatostatin. Recall that somatostatin inhibits growth hormone release and causes muscle breakdown. Therefore, over doing it in the weight room can actually lead to muscle degradation rather than muscle growth.

Note: Sensible exercise and adequate rest go hand in hand in building muscle.

Other Releasers: Growth hormone is also released in response to these other physiological stimuli:

* Fasting
* Low blood sugar
* Stress
* Injury or Trauma
* Fever
* Dopaminergic Agonists (Neurotransmitters)
* L-arginine?