Growth hormone is one of the most important anabolic and reparative hormones in the human body. It stimulates the liver to produce IGF-1, which in turn promotes muscle protein synthesis, adipose tissue lipolysis, bone mineralisation, collagen synthesis, and immune cell proliferation. Growth hormone secretion declines by approximately 14 to 15 percent per decade from the age of 30, a phenomenon termed somatopause. By the age of 60, the average person secretes approximately one-third the growth hormone they did in young adulthood. This decline is associated with the body composition changes, reduced recovery capacity, and poorer connective tissue integrity that characterise normal ageing.
Why Natural Growth Hormone Decline Matters
The clinical consequences of the age-related decline in growth hormone secretion include increased visceral adiposity, reduced lean muscle mass, decreased bone density, impaired recovery from illness and injury, reduced exercise capacity, and poorer sleep quality, particularly in slow-wave sleep, which is the primary period of growth hormone secretion. These changes are not inevitable in the same way that cellular senescence is inevitable; they are partly driven by lifestyle factors including poor sleep, physical inactivity, chronic stress, and impaired nutrition, which all suppress growth hormone secretion independently of age.
Growth Hormone Releasing Peptides
Growth hormone secretagogues stimulate growth hormone release through two main receptor pathways. Growth hormone releasing hormone analogues such as CJC-1295 and sermorelin act on the GHRH receptor in the pituitary. Ghrelin mimetics such as ipamorelin and GHRP-6 act on the growth hormone secretagogue receptor. Both approaches produce growth hormone release in a pulsatile, physiological pattern that preserves negative feedback regulation, unlike exogenous growth hormone administration which suppresses endogenous production. Clinical trials in adults with GH deficiency using sermorelin and CJC-1295 have demonstrated significant improvements in lean body mass, fat mass, and in some studies bone mineral density.
Natural Lifestyle Optimisation of the GH Axis
- Deep sleep: 70 to 80 percent of daily growth hormone secretion occurs during slow-wave sleep, particularly in the first sleep cycle; improving sleep quality through consistent sleep timing, a cool dark bedroom, and magnesium supplementation directly supports GH output
- High-intensity interval training: sprint intervals and heavy resistance training are the most potent natural stimuli for GH secretion; a meta-analysis in Metabolism found that HIIT produced significantly greater GH responses than moderate-intensity continuous exercise
- Fasting: the pituitary secretes a large GH pulse during the overnight fast; prolonged fasting amplifies this; eating carbohydrates immediately before bed suppresses the overnight GH pulse through insulin's inhibitory effect on GH secretion
- Adequate protein: arginine and lysine at doses of 2 grams each can modestly stimulate GH secretion acutely; these amino acids are abundant in high-quality protein sources
- Vitamin D adequacy: low vitamin D is associated with lower IGF-1 levels in population studies; optimising vitamin D to 100 to 150 nmol/L may support the GH-IGF-1 axis
- Reducing visceral fat: visceral adiposity is one of the strongest inhibitors of GH secretion through the somatostatin pathway; reducing visceral fat through dietary and exercise interventions significantly improves GH pulsatility
Considerations for Therapeutic Use
Licensed use of growth hormone secretagogues in the UK is restricted to the treatment of diagnosed growth hormone deficiency. Off-label and unregulated use carries risks including oedema, carpal tunnel syndrome, insulin resistance, and the theoretical risk of stimulating growth of occult neoplasms, as IGF-1 is mitogenic. Anyone considering growth hormone secretagogue therapy should do so only under qualified medical supervision after assessment of baseline GH and IGF-1 levels.
Sources
- Giustina, A., & Veldhuis, J.D. (1998). Pathophysiology of the neuroregulation of growth hormone secretion in experimental animals and the human. Endocrine Reviews, 19(6), 717-797.
- Walker, R.F. (2006). Sermorelin: a better approach to management of adult-onset growth hormone insufficiency? Clinical Interventions in Aging, 1(4), 307-308.
- Sigalos, J.T., & Pastuszak, A.W. (2018). The safety and efficacy of growth hormone secretagogues. Sexual Medicine Reviews, 6(1), 45-53.
- Goldenberg, N., & Barkan, A. (2007). Factors regulating growth hormone secretion in humans. Endocrinology and Metabolism Clinics of North America, 36(1), 37-55.
- Van Cauter, E., et al. (2000). Age-related changes in slow wave sleep and REM sleep. JAMA, 284(7), 861-868.