Growth Hormone: How Does It Work and Why Do Women Have More?
Growth Hormone (GH). You’ve probably heard of it if you’re into fitness. Maybe you’ve read some articles about maximizing your production of growth hormone to improve muscular hypertrophy and decrease body fat. Perhaps, you’ve also heard of people injecting growth hormone or taking growth hormone boosting supplements to improve body composition and performance or to stall the aging process. But, do you really know what it does in the human body or when, why and how it’s produced? And did you know production varies due to gender and probably not in the way you’d expect?
Growth Hormone Production
First, let’s briefly review the basics of growth hormone secretion. Growth hormone is produced and secreted from cells located in the anterior pituitary. It’s released in pulses. These pulses are controlled by the hypothalamus, which sends signals to either shut off the release or initiate a pulse of growth hormone into the bloodstream. So, basically the hypothalamus is the boss of the anterior pituitary.
When the body has “enough” growth hormone and/or insulin-like growth factor (IGF-1), the hypothalamus sends a little messenger called somatostatin to tell the anterior pituitary to stop releasing growth hormone. When there isn’t enough growth hormone in the bloodstream, then the hypothalamus sends a different messenger, growth hormone releasing factor (GHRF), to tell the anterior pituitary to release some of the good stuff. Make sense?
The Purpose of Growth Hormone
What does growth hormone do? Well, in a nutshell, growth hormone causes things to grow, hence the name. And how exactly does growth hormone cause things to grow? Through several different mechanisms including:
- Increased protein synthesis
- Increased lipolysis (decreases fat)
- Increased sarcomere growth
- Reduced liver uptake of glucose and enhanced formation of new glucose (gluconeogenesis)
- Supporting the pancreas and its production of different hormones like insulin, glucagon, ghrelin, etc.
In other words, growth hormone supports and initiates growth of tissue in the human body in many ways and can decrease adipose tissue as well. Optimal levels are generally considered to be beneficial for athletes and pretty much anyone who wants to maintain a favorable body composition, bone health, and general physical well being.
What Affects Growth Hormone
Now, what affects the production of growth hormone? Many different things! Deep and adequate sleep, intense exercise, fasting, low blood sugar, the hormone ghrelin, the amino acid arginine, and some B vitamins like niacin. Also, natural testosterone and estrogen increase growth hormone levels. Things that decrease growth hormone include chronic stress, poor and inadequate amounts of sleep, high blood sugar levels, glucocorticoids, and a form of testosterone known as DHT. Bare in mind that while fasting and vigorous exercise can increase growth hormone, that is only to a certain point, and once the these mild stressors become chronic and too much for the body to handle, any anabolic mechanism is generally going to be shut down as the body attempts to, for lack of a fancy scientific term, save it’s ass from stressing or starving to death.
Men vs. Women
So here’s the interesting thing - women make more growth hormone than men. Weird, huh? It seems counterintuitive. Aren’t men the bigger, stronger sex? Well, that’s probably a controversial question, but in most instances, yes, men are physically stronger and have higher testosterone levels. So, you would think (or at least I did) that men also make more growth hormone. However, numerous studies have found that mean concentrations of growth hormone are anywhere from six-fold to 120-fold higher in premenopausal women than men.
Why is this? Well, studies point to estrogen as the main reason women generally make more growth hormone than men. Studies have compared growth hormone levels in premenopausal women to men of the same age and found that women have higher mean growth hormone levels and higher GH secretory burst amplitudes. Some studies even dosed men with estrogen and found that their growth hormone did indeed increase with the added hormone. In addition, women’s mean GH levels increase even more when we are in the phases of our menstrual cycles where our estrogen is highest or when we are on birth control pills that contain estrogen.
Also, our pattern of growth hormone secretion is different from that of men. Men have large nocturnal pulses of growth hormone and do not tend to produce as much during the day, while women spend about two times as much time during the day actively secreting growth hormone. Women were also found to have a greater GH response to exercise at all intensities and women reach peak GH concentrations earlier in exercise.
Interesting information, right? But what does this really mean for women? How we can use this information to help ourselves become fitter and healthier? What happens when our estrogen takes a nosedive and is there anything we can do about it? And, if growth hormone is so anabolic why aren’t we as lean, muscular, and strong as our male counterparts? Ladies, stay tuned for the next article when I attempt to answer some of these questions and discuss how to optimize exercise, nutrition, supplementation, and even hormone replacement later in life in order to reap the full benefits of growth hormone.
1. Vab den Berg, G., Veldhuis, J., Frloch, M., and Roelfsema, F. “An amplitude-specific divergence in the pulsatile mode of growth hormone (GH) secretion underlies the gender difference in mean GH concentrations in men and premenopausal women.” Journal of Clinical Endocrinology and Metabolism 7 (1996): 2460-7. Accessed October 1, 2013.
2. Veldhuis, J. “New modalities for understanding dynamic regulation of the somatotropic (GH) axis: explication of gender differences in GH neuroregulation in the human.” Journal of Pediatric Endocrinology and Metabolism Jun;9 Suppl 3:237-53. Accessed October 1, 2013.
3. Veldhuis, J, Patrie,, W., Patterson, M., Weltman, J., and Weltman, A. “Contrasting negative-feedback control of endogenously driven and exercise-stimulated pulsatile growth hormone secretion in women and men.” Journal of Clinical Endocrinology and Metabolism 2004 Feb;89(2):840-6. Accessed October 1, 2013.
4. Veldhuis, J. “Neuroendocrine control of pulsatile growth hormone release in the human: relationship with gender.” Growth Hormone and IGF Research 1998 Apr;8 Suppl B:49-59. Accessed October 1, 2013.
Graphic 1 by Mikael Häggström (All used images are in public domain.) [Public domain], via Wikimedia Commons.
Graphic 2 courtesy of Shutterstock.