Pathophysiology
As an adult ages, it is normal for the pituitary to produce diminishing amounts of GH and many other hormones, particularly the sex steroids. Physicians therefore distinguish between the natural reduction in GH levels which comes with age, and the much lower levels of "true" deficiency. Such deficiency almost always has an identifiable cause, with adult-onset GHD without a definable cause ("idiopathic GH deficiency") extremely rare. GH does function in adulthood to maintain muscle and bone mass and strength, and has poorly-understood effects on cognition and mood.
Read more about this topic: Growth Hormone Deficiency