IGF-1

How IGF-1 Works

IGF-1 functions through the GH-IGF-1 axis:

1. Growth hormone release - GH is released from the pituitary
2. Liver stimulation - GH binds to liver receptors
3. IGF-1 production - Liver produces and releases IGF-1
4. Tissue effects - IGF-1 acts on muscles, bones, and other tissues
5. Feedback regulation - IGF-1 inhibits further GH release

IGF-1 Functions

Growth and Development

• Promotes bone growth and mineralization
• Stimulates muscle cell proliferation
• Essential for normal development

Metabolic Effects

• Enhances protein synthesis
• Promotes glucose uptake in muscles
• Influences fat metabolism

Tissue Repair

• Supports wound healing
• Promotes cell regeneration
• May have neuroprotective effects

IGF-1 vs Insulin vs Growth Hormone

Property	IGF-1	Insulin	GH
Primary source	Liver	Pancreas	Pituitary
Main trigger	GH	Glucose	GHRH
Growth effects	Strong	Weak	Indirect (via IGF-1)
Glucose effects	Lowers (weak)	Lowers (strong)	Raises
Protein synthesis	Increases	Increases	Increases

IGF-1 Binding Proteins

IGF-1 circulates bound to binding proteins (IGFBPs):

• IGFBP-3 - Most abundant, extends IGF-1 half-life
• IGFBP-1 through 6 - Regulate IGF-1 availability
• Only ~1% is free - Unbound IGF-1 is biologically active

These binding proteins:

• Extend IGF-1 half-life from minutes to hours
• Regulate tissue availability
• Can enhance or inhibit IGF-1 activity

IGF-1 and Peptide Research

Many peptides indirectly affect IGF-1 levels:

GHRH Analogs (CJC-1295, Sermorelin)

• Increase GH release
• Lead to increased IGF-1 production
• Effects are downstream of GH elevation

Growth Hormone Secretagogues (Ipamorelin, GHRP-6)

• Stimulate GH release via ghrelin pathway
• Also result in elevated IGF-1
• Different mechanism than GHRH analogs

Measuring IGF-1

IGF-1 is often used as a biomarker:

• More stable than GH (which pulses throughout day)
• Reflects overall GH status
• Normal range varies by age and sex

Frequently Asked Questions

Is IGF-1 the same as growth hormone?

No. IGF-1 is produced in response to growth hormone and mediates many of GH’s effects, but they are different hormones. GH is produced by the pituitary; IGF-1 is mainly produced by the liver. Think of GH as the “signal” and IGF-1 as the “effector.”

Why measure IGF-1 instead of growth hormone?

GH is released in pulses and levels vary dramatically throughout the day, making single measurements unreliable. IGF-1 levels are much more stable and better reflect overall GH status over time.

Can you increase IGF-1 naturally?

Yes. Adequate sleep, resistance exercise, and sufficient protein intake support healthy IGF-1 levels. Certain amino acids (particularly arginine and leucine) may acutely stimulate the GH-IGF-1 axis.