IGF-1 (Insulin-Like Growth Factor 1)

•Observational— Centenarian and cancer-risk data

What it measures

IGF-1 is a peptide hormone produced primarily by the liver in response to growth hormone. It mediates most of GH's anabolic effects (bone, muscle, organ growth) and is a potent mitogen across tissues.

The longevity J-curve

• Very high IGF-1: associates with higher cancer risk (breast, prostate, colorectal) and reduced lifespan.
• Mid-low IGF-1: longest survival in centenarian cohorts (Milman 2014).
• Very low IGF-1: frailty, sarcopenia, increased fracture risk in older adults.

The sweet spot in midlife appears to be the lower half of the age- adjusted reference range — not aggressively low.

What modifies IGF-1

• Down: protein restriction, methionine restriction, caloric restriction, plant-based diets.
• Up: high animal-protein intake, growth hormone, certain peptides (sermorelin, CJC-1295).
• Resistance training has modest effects.

Use in clinical practice

• Hypogonadism evaluation (alongside cortisol, prolactin) in pituitary workup.
• Acromegaly screening (GH excess).
• Adult GH deficiency monitoring.
• Longevity-medicine practice for tracking response to dietary changes and GH/peptide use.

Related entries

Insulin/IGF-1 signalling, Protein and mTOR, Methionine restriction, GH/GHRH analogs.