Predictors of Growth Hormone Secretion in Aging

Summary: Growth hormone again

Interestingness: 2

Paper by Mark L Hartman, Jody L Clasey, Arthur Weltman and Michael O Thorner in the Journal of Anti-Aging Medicine, Volume 3, Issue 3, Spring 2000.


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Growth hormone (GH) secretion goes down with age at an inversely logarithmic rate. It is almost down all the way by time we are in our 30s. This may not be due to age alone though, since there are high correlations between integrated GH concentration and each of BMI, percentage body fat and fitness, as measured by oxygen consumption, especially in men (in women the effect does not reach the magic 0.05).

Most of the reasons listed for the decrease we've seen before already (growth hormone papers). Some that I haven't:

• GH secretions four times higher during stage 3 and 4 sleep. Deep sleep goes to the shit with age.
• Possible path by which high fat reduces GH: high free insulin-like growth factor 1 (IGF-1). But then they quote study showing inverse correlation between free IGF-1 and visceral fat.

In their own studies, they find correlations between integrated GH concentration and each of abdominal visceral fat, fasting insulin and IGF-1, independent of age, sex, total body fat mass, percentage fat, 24 hour mean estradiol and testosterone, and peak oxygen uptake, in a group of 40 people in their 20s and 62 in the 57-80 year old range. Also, a high correlation between the combination of age and sex with IGF-1.

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Abstract follows:

Growth hormone (GH) secretion decreases progressively after mid-puberty in both men and women. This decrease occurs predominantly before age 40-50 and affects both daytime and nocturnal GH secretion. A reduction in the amplitude of GH secretory pulses accounts for the majority of the reduction in GH secretion. With aging, changes in hypothalamic function may occur that result in decreased GH secretion. These changes may include decreased secretion of GH-releasing hormone and/or the putative natural ligand for the GH secretagogue receptor or an increase in somatostatin release. Multiple physiological factors have been reported to regulate GH secretion including sleep, body composition (% body fat and amount of abdominal visceral fat), aerobic physical fitness and serum concentrations of insulin-like growth factor-I (IGF-I), gonadal steroids and insulin. Changes in these factors with aging may contribute to the reduction in GH secretion observed in older adults. However, these physiological predictors of GH secretion are not independent of one another and the relative importance of these factors in the regulation of GH secretion is not known. Preliminary evidence suggests that the amount of abdominal visceral fat and fasting serum concentrations of insulin and IGF-I are the most important predictors of 24-hour GH release in healthy adults, independent of age and gender. Bi-directional feedback between these three factors and GH secretion may account for the strong relationships observed.