Insulin-Like Growth Factor 1 (IGF-1)

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What it isIGF-1 is a peptide hormone produced primarily by the liver in response to growth hormone signaling. It carries out most of growth hormone's downstream effects on tissue growth.

DoesDrives muscle protein synthesis, bone growth, neurogenesis, and tissue repair; also drives cell proliferation more broadly.

GoodMid-range IGF-1 supports muscle, bone, and tissue repair without excess growth signaling.

BadBoth low and high IGF-1 track mortality. Low IGF-1 signals frailty, poor recovery, and increased cardiovascular risk. High IGF-1 drives accelerated aging and cancer risk; very high suggests acromegaly.

Standard

Age- and sex-dependent; 100–280 ng/mL adult midlife.

Optimal

150–220 ng/mL adult midlife (narrow target)

Modifiers

Declines with age; rises with adequate protein, sleep, and resistance training; suppressed by caloric restriction and fasting.

How to optimize

Lifestyle: Resistance training (raises IGF-1), 7–9 hours of sleep (most growth hormone released in deep sleep), avoid extreme caloric restriction in older adults.
Diet: Adequate protein (1.6–2.0g/kg) and calories; avoid both extreme calorie restriction and excess.
Supplements: Adequate protein; whey protein post-training; arginine, glycine, glutamine.
Peptides: CJC-1295, ipamorelin, sermorelin, tesamorelin, ghrelin mimetics raise growth hormone and thereby IGF-1; IGF-1 LR3 used directly in some advanced protocols.
Drugs: Growth hormone replacement (rare in non-deficient adults); pegvisomant blocks excess signaling.

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