IGF-1 (Insulin-like Growth Factor 1)
The cellular growth hormone — paradox between vitality and accelerated ageing
Definition
IGF-1 is a peptide hormone produced mainly by the liver in response to growth hormone (GH). It is the effector mediator of most GH effects: it promotes muscle protein synthesis, bone growth, tissue repair, and cellular proliferation. Its relationship with longevity is complex: very low levels predict sarcopenia, frailty, and functional decline, but very high levels are associated with higher cancer risk and reduced exceptional longevity.
Detailed explanation
The Ashkenazi centenarian study (Suzuki & Barzilai) revealed that many long-lived individuals carry IGF-1 receptor polymorphisms that reduce downstream signalling; mice with partial IGF-1 receptor knockdown live significantly longer. Laron dwarves (GH receptor deficiency, almost no IGF-1) show remarkable resistance to cancer and diabetes despite short stature.
Longevity-optimal values by age: 20-35 years: 200-300 ng/mL (anabolic, at peak) 35-50 years: 150-250 ng/mL >50 years: 120-200 ng/mL (balance zone, avoiding both the frailty and pro-tumoural zones)
Very low IGF-1 (<100 ng/mL in those over 50) predicts sarcopenia, osteoporosis, depression, dyspermia, and frailty. Very high IGF-1 (>250-300 ng/mL in those over 50) is associated with increased risk of breast, prostate, and colon cancer and total mortality.
Interventions that raise IGF-1: strength exercise (chronic effect), adequate animal protein, deep sleep (GH is released mainly in N3), GH secretagogues (CJC-1295, Ipamorelin, Tesamorelin), HRT in hypogonadism.
Interventions that lower IGF-1: protein restriction, prolonged fasting, moderate caloric restriction, rapamycin. The optimal longevity strategy is to cycle IGF-1 — periods of anabolic activity (exercise, sufficient protein) alternating with catabolic periods (fasting).
Scientific sources
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