Growth Hormone and Aging
Growth hormone declines with age in every animal species that have been tested to date. In humans, the amount of growth hormone after the age of 21 to 31 falls about 14% per decade, so that the total 24-hour growth hormone production rate is reduced in half by the age of 60. In numerical values, we produce on a daily basis about 500 micrograms at 20 years of age , 200 micrograms at 40 years , and 25 micrograms at 80 years old.
The easiest way to measure growth hormone in the body is by measuring plasma IGF-1 levels. Under 350 IU is considered evidence of deficiency. Between the ages of 20 to 40 years, less than 5% of healthy men have less than 350 IU per liter of IGF-1 levels. But after 60, 30% of apparently healthy men have this low amount. And after age 65, about half the population is partially or wholly deficient in growth hormone.
Total daily hGH secretion declines in humans with increasing age. "Elederly" levels are reached by age 35-40.