Effects of age on GH secretion
Several studies have shown that the amplitude of GH pulses is reduced with aging both in men and women. In aging men, GH secretion declines by 50% every 7 years after age 18-25 years. The negative effect of age on 24-hour mean serum GH is twice as much in men as in premenopausal women. Estrogens may have a protective effect that limits the rate of decline of GH secretion with aging.
IGF-1 and IGFBP-3 levels also decrease with aging. This decline of the GH–IGF-1 axis is probably caused by altered hypothalamic regulation (ie, decrease in GHRH and increase in somatostatin), rather than a decreased capacity to secrete GH.
The pathophysiology of the somatopause is confounded by several variables that can contribute to the decline in GH secretion associated with aging. These variables include the following:
Adiposity: Individuals who are moderately to markedly obese have profound suppression of GH secretion at any age.
Decreased production of sex steroid hormones: Falling levels of Testosterone in men and estrogens in women affect GH secretion.
Decreased physical fitness: A strong correlation exists between aerobic capacity and 24-hour serum GH concentration.
Fragmented sleep: GH secretion can by affected by altered sleep patterns because it occurs predominantly during slow-wave sleep.
Malnutrition: Poor nutritional status negatively affects IGF-1 synthesis and action.
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