Human Growth Hormone (HGH)
Before we discuss the decline of human growth hormone (hGH) with aging and what can be done about it, we think it would be helpful to review some physiology. hGH is produced in the pituitary gland by the somatotroph cells (hGH’s medical name is somatotropin).
Under the influence of the hypothalamus (the part of the brain concerned with the more primitive bodily functions), hGH is released in spurts, predominantly at night during the third and fourth stages of deep sleep.
As it circulates through the blood, hGH stimulates the production of insulin-like growth factor I (IGF-I) by the liver and other cells of the body. Because it is released in spurts, hGH is difficult to measure except in a research setting where blood can be drawn every 10 minutes. The blood level of IGF-I, in contrast, is more constant, and therefore, except under certain circumstances, it serves as a reliable surrogate measure of hGH production.
The assessment of one’s growth hormone secretion is an important part of any preventive health evaluation for two reasons. The first is that the signs and symptoms of a declining GH level are not as obvious as, for example, the cessation of periods or hot flushes in a women when her estrogen level falls.
The second is that with regard to GH, people age at very different rates. While on average the decline is 50% every 7 to 10 years (so that by age 50 the majority of people have significantly lowered GH secretion), a 35 year old may have a GH level of an average 70 year old and the same holds true in reverse.
Body composition, in particular the amount of abdominal fat, as well as aerobic fitness significantly impact one’s GH secretion; the more abdominal fat you have the less GH you secrete, and the more fit you are, the more GH you secrete.
If you are diagnosed with Growth Hormone Deficiency of Adulthood, you may be prescribed hGH therapy. The amount of hGH we prescribe and the benefits you can expect depend on your starting level of IGF-I.
Once on therapy, the benefits we often see are as follows:
- Decreased fat mass, 10 to 14 percent after approximately 6 months, predominantly around the waist, without change in diet and exercise
- Increased lean muscle mass of approximately 7 to 10 percent in the first six months of therapy
- Improved bone density after one year of therapy, depending pre-treatment density
- Improved cardiac and lung function, lowered diastolic blood pressure
- Increased physical and mental energy level
- Increased hydration of the skin
- Accelerated wound healing
- Increased immune system functioning, including re-growth of the thymus (the gland important in the function of T-cells)
- Decreased total and LDL cholesterol levels, and increased HDL levels
- Improved sleep
- Improved vision
- Improved mood
The degree to which you see these improvements will depend on your level of growth hormone deficiency as measured by your IGF-I level and clinical exam. If your level is below 100 ng/ml, you will likely see significant changes in body composition in the first six months. If you have a higher level, the effect of the supplementation may be to prevent these age-related changes from occurring.