Longevity Medicine
What Is Insulin-Like Growth Factor 1 (IGF-1)?
Last reviewed: May 2026 · Haute MD Editorial Team
Insulin-like growth factor 1 (IGF-1) is a hormone produced primarily by the liver in response to growth hormone, mediating most of growth hormone's anabolic and growth-promoting effects. IGF-1 is one of the most studied molecules in longevity science because of a striking paradox — reducing IGF-1 signaling extends lifespan in nearly every species studied, but very low IGF-1 in older adults is associated with frailty, sarcopenia, and increased mortality. The 'sweet spot' for IGF-1 across the lifespan is a central question in longevity medicine.
What IGF-1 does in the body
IGF-1 mediates childhood growth, muscle protein synthesis, bone formation, cellular proliferation, and tissue repair. It signals through the IGF-1 receptor to activate the PI3K/Akt/mTOR pathway — the same anabolic pathway activated by insulin and amino acids — driving growth, cell division, and protein synthesis. IGF-1 levels peak in adolescence, decline gradually through adulthood, and fall further in older age. Low IGF-1 in adulthood often reflects reduced growth hormone secretion (somatopause), poor protein intake, or chronic illness. High IGF-1 reflects either acromegaly, exogenous growth hormone use, high protein/anabolic diet, or genetic predisposition.
The IGF-1 longevity paradox
In model organisms — worms, flies, mice — reducing IGF-1 signaling (via genetic knockouts of IGF-1 receptor or downstream signaling) dramatically extends lifespan, often by 30-50%. The Laron syndrome population (humans with growth hormone receptor mutations and near-absent IGF-1) shows striking protection against cancer and type 2 diabetes — though they are short-statured and obese. In typical aging adults, however, the relationship is U-shaped: very high IGF-1 is associated with increased cancer risk (particularly breast, prostate, colorectal), while very low IGF-1 in older adults is associated with sarcopenia, cardiovascular disease, and increased all-cause mortality. The optimal range for an adult appears to be the middle quartiles — not the highest, not the lowest.
How to interpret and optimize IGF-1
Reference ranges are age-stratified and laboratory-specific. Most longevity-focused physicians target the middle quartile of the age-adjusted reference range — roughly 100-200 ng/mL in adults 30-60, declining modestly with age. Interventions that lower IGF-1 — caloric restriction, intermittent fasting (particularly 24+ hour fasts), plant-forward dietary patterns, lower animal protein intake, and rapamycin — are also associated with longevity benefit. Interventions that raise IGF-1 — exogenous growth hormone, high animal protein intake, resistance training (modestly) — are appropriate for treating documented deficiency but should not be used to push levels above the population median in healthy adults without indication. Exogenous growth hormone for 'anti-aging' in adults with normal pituitary function is not supported by current evidence and may increase cancer risk.
Frequently Asked Questions
Should I take growth hormone to feel younger?
No. Exogenous growth hormone for adults without documented growth hormone deficiency is not supported by evidence, is associated with insulin resistance, fluid retention, joint pain, and may increase cancer risk. The clinical use of GH is appropriately limited to documented deficiency (pituitary disease) under endocrinologist care. 'Anti-aging' GH protocols are off-label and not recommended.
Does eating more protein raise IGF-1?
Yes — high protein intake, particularly animal protein, modestly raises IGF-1 levels. Very low protein intake reduces IGF-1 but also accelerates sarcopenia in older adults. The longevity-optimal protein target — typically 1.2-1.6 g/kg in middle age, 1.6-2.0 g/kg in older adults to preserve muscle — produces moderate, healthy IGF-1 levels in most adults.
Should IGF-1 be measured routinely?
IGF-1 is part of a comprehensive longevity biomarker panel and is useful for tracking response to nutrition, exercise, fasting, and supplement interventions. It is not currently part of standard primary care but is increasingly measured in longevity-focused practices.
What if my IGF-1 is low?
Low IGF-1 in adulthood warrants evaluation of pituitary function, protein intake, overall caloric adequacy, thyroid function, and chronic illness. Mildly low IGF-1 in an otherwise healthy adult on a moderate-protein, plant-forward diet may simply reflect dietary pattern and not require intervention. Substantial deficiency with symptoms (fatigue, sarcopenia, reduced quality of life) warrants endocrinology evaluation.
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