Longevity Science

IGF-1 (Insulin-Like Growth Factor 1)

A hormone mediating the growth effects of growth hormone. In dogs, higher lifelong IGF-1 levels correlate with larger body size and shorter lifespan. The LOY-001 drug targets excess IGF-1 in large breeds.

Insulin-Like Growth Factor 1 (IGF-1) is a peptide hormone produced primarily by the liver in response to growth hormone (GH) signaling. IGF-1 mediates most of the growth-promoting effects of GH during development and maintains anabolic (tissue-building) signaling throughout life.

IGF-1 and Canine Size-Longevity Relationship

The remarkable size-longevity correlation in dogs — where each additional 4.4 lbs of body weight reduces lifespan by approximately one month (Kraus et al., 2013) — is mediated substantially through IGF-1:

  • Large breed dogs have significantly higher circulating IGF-1 throughout life
  • Breeds with genetic variants producing less IGF-1 tend to be smaller and longer-lived
  • Within breeds, smaller individuals often live longer than larger individuals
  • The GH/IGF-1 axis is one of the most conserved longevity pathways across species (from worms to dogs to humans)

Molecular Mechanisms

High IGF-1 signaling promotes:

  • Cellular proliferation: increased cancer risk (more cell divisions = more mutation opportunities)
  • Reduced autophagy: cellular “self-cleaning” is suppressed; damaged protein accumulation accelerates
  • Oxidative stress: higher metabolic rate from tissue-building IGF-1 signaling increases reactive oxygen species
  • Accelerated cellular senescence: higher IGF-1 accelerates the rate at which cells reach their replicative limit

Loyal LOY-001

Loyal Biosciences (San Francisco) is developing LOY-001, a monthly injectable drug for large and giant breed dogs designed to reduce circulating GH and IGF-1 to levels more comparable to small breeds. The clinical logic: if small dogs’ lower IGF-1 accounts for their longer lifespan, reducing IGF-1 in large dogs may extend their lifespan toward small-dog norms.

Current status (2026): LOY-001 has completed FDA Target Animal Safety (TAS) evaluation. The STAY clinical trial (1,300 large/giant breed dogs) is measuring longevity outcomes. Conditional approval pending completion of effectiveness data.

IGF-1 and Small Dogs

Small dogs with naturally low IGF-1 have their own longevity challenges — primarily dental disease and cardiac disease — but the systemic aging rate reflected in cancer risk, organ failure, and tissue senescence appears slower. The Chihuahua’s 14–17 year lifespan vs. the Great Dane’s 7–9 year lifespan represents a roughly 2x longevity difference attributable substantially to this IGF-1 differential.