Human Growth Hormone Facts
Human growth hormone facts are hard to come by being overshadow by many myths surrounding this important hormone some call the master regulator.
Human growth hormone (HGH) is produced in the anterior pituitary and is a peptide hormone of 191 amino acids. The pituitary gland is a small pea size gland more or less in the center of the brain that plays a pivotal role in hormone production and release.
When we think of growth hormone we think of ….. growth. But growth hormone does much more than regulate skeletal growth. We still produce growth hormone daily as adults even though we have longed quit growing, so why? Why do we still produce growth hormone? Growth hormone is our main repair and rejuvenating hormone.
Before we go too much farther, human growth hormone is better thought of as a pro-hormone that gets converted into IGF-1 in the liver and peripheral tissues. It is IGF-1 that is responsible for many of the actions attributed to growth hormone, though growth hormone itself is responsible for some its function.
Now for some human growth hormone facts.
Growth Hormone Pulses
Growth hormone is secreted in pulses that last 20 to 60 minutes. The average person produces 4 to 6 of these pulses a day. The pulses are random, but one predictably occurs early in one’s sleep cycle during slow wave sleep. That’s one reason why getting good sleep is essential to health. Slow wave sleep is also improved by growth hormone replacement therapy. Vigorous exercise also triggers a pulse of growth hormone release. This is one reason we repeatedly emphasize vigorous exercise – strength training and high intensity interval training.
In between pulses growth hormone production is essentially zero – which makes measuring growth hormone levels a bit tricky.
As mentioned, growth hormone gets converted into IGF-1, which stands for insulin growth factor-1. IGF-1 levels are generally stable throughout the day and it is IGF-1 that is measured in the blood to gauge growth hormone production.
Symptoms of Low Growth Hormone
There are many symptoms and signs associated with low growth hormone. See “Low HGH Symptoms”. The more common signs include decreased mood and well-being, loss of lean body mass and strength, increased body fat, decreased skin thickness, and abnormal glucose and insulin metabolism.
Growth Hormone Levels
Growth hormone and IGF-1 levels vary with age.
The reference range for IGF-1 is below. The reference range encompasses the middle 95% of the population.
- 16-24 year olds: 182-780 ng/ml
- 25-39 year olds: 114-492 ng/ml
- 40-54 year olds: 90-360 ng/ml
- >54 year olds: 71-290 ng/ml
What is a healthy IGF-1 level? The above reference ranges represent a statistical range but say nothing about what a healthy IGF-1 is or should be. A level of 194 ng/dl or higher is associated with the lowest levels of health risk based on one review reference ranges. When treating adults with growth hormone deficiencies the goal is to treat to an IGF-1 level of at 250 ng/ml or more.
Low Growth Hormone and Mortality
Low growth hormone is an independent risk factor for mortality. The Framingham study found a 13% lower mortality rate in individuals with IGF-1 levels in the upper half of the reference range versus those in the lower half of the reference range.
In the Ranch Bernardo Study, each 40 ng/ml decrease in IGF-1 below the mean was associated with a 38% increase in mortality. This increased mortality was concluded to be primarily related to increased heart disease mortality
There is an inverse relationship with IGF-1 levels and stroke outcome and mortality. Mortality from stroke is reduced 30% for each 20 ng/ml increase in IGF-1 levels.
Growth Hormone and Sleep
Growth hormone levels and slow wave sleep are closely related. Slow wave sleep occurs for long periods in the early parts of the night and those periods are longest in children and young adults. Slow wave sleep diminishes with age and with lower levels of growth hormone are released. Slow wave sleep is restored in those treated with growth hormone who have a growth hormone deficiency.
Growth Hormone and the Brain
Growth hormone replacement has been shown to improve memory, mental processing speed, alertness, and motivation. Growth hormone also improves neural cell communication. Stimulation of IGF-1 receptors decreases cell death caused by beta amyloid protein. Beta amyloid is associated with Alzheimer’s disease. While growth hormone may decrease the risk of Alzheimer’s disease it has not been conclusively shown to lessen the progression of Alzheimer’s disease.
There is a direct correlation between IGF-1 levels and cognitive function. The higher the IGF-1, the better the cognitive function.
Growth Hormone and the Heart
More and more studies are showing growth hormone replacement to be beneficial in patients with congestive heart failure. This improvement is the result of improve contractility of the heart tissue. IGF-1 levels also provide protection of blood vessels.
Growth Hormone and Bone
Growth hormone replacement is associated with improved bone density, though there can be a transient decline in bone density the first 6 months of treatment. This is because bone is being formed and resorbed at the same time, and growth hormone initially stimulates the resorption process to a greater degree than the formation process. But, with time the formation process outpaces the resorption process.
Growth Hormone and Immune Function
Growth hormone replacement improves immune function through a couple mechanisms. It improves function of the thymus, which produces T-cells, an integral component of our immune system. Growth hormone replacement also reduces levels of inflammatory cytokines like tumor necrosis factor, interleukin-6 factor and inflammatory markers like C-reactive protein.
Growth Hormone and Metabolism/Body Composition
Growth hormone replacement studies have consistently shown improvements in body composition consisting of decreased body fat and increased muscle mass. Improvements in VO2 max, a measure of cardiovascular fitness, have been demonstrated consistently as well. Growth hormone replacement improves insulin sensitivity. However, too high of a dose of growth hormone will decrease sensitivity.