Insulin/IGF-1 Signaling in Aging

Insulin and IGF-1 bind related receptors that activate the PI3K-AKT-FOXO signaling cascade, promoting cell growth, glucose uptake, and protein synthesis while suppressing stress-resistance and autophagy programs. Loss-of-function mutations in this pathway extend lifespan in every model organism tested at some dose: C. elegans daf-2 mutants live roughly twice as long as wild type, Drosophila with reduced insulin receptor signaling live up to 85% longer in some studies, and mice with reduced growth hormone or IGF-1 receptor signaling (Ames dwarf, Snell dwarf, and IGF-1 receptor heterozygous mice) live 25-65% longer than controls depending on the specific mutation and sex [1].

The clearest human parallel comes from Ecuadorian patients with Laron syndrome (growth hormone receptor deficiency, which blocks IGF-1 production): a 22-year prospective study found these individuals had only one nonlethal cancer and zero cases of diabetes, versus 17% cancer prevalence and 5% diabetes prevalence in unaffected relatives, alongside markedly lower fasting insulin (1.4 µU/ml vs. 4.4 µU/ml) [2]. This human cohort data lines up directly with the animal-model pattern, making IIS one of the few aging pathways with both strong animal and human genetic evidence pointing the same direction.

What the evidence does not show: Laron syndrome patients are short in stature and the cohort, while informative, is small (fewer than 100 individuals) and specific to one set of mutations in one population, so it cannot establish population-wide dose-response for IGF-1 reduction in typical humans. Reduced IGF-1 signaling in elderly populations without these specific mutations is also linked to increased frailty, sarcopenia, and reduced bone density, meaning the same pathway that appears protective against cancer when disrupted from birth may be harmful when it declines naturally in already-aged tissue, a form of antagonistic pleiotropy [1].

Blueprint's approach engages this pathway indirectly through caloric intake control and time-restricted eating rather than any drug targeting IGF-1 receptor signaling directly; growth hormone or IGF-1 suppression drugs are not part of Bryan Johnson's published protocol [3]. A broader review of the genetics of aging places the insulin/IGF-1 pathway alongside mTOR and sirtuins as one of the small number of conserved longevity-regulating networks identified across nearly every model organism studied to date, a 2016 review of reduced insulin/IGF-1 signaling and human longevity noted the same conservation pattern while cautioning that human effect sizes are far smaller than the doubling of lifespan seen in C. elegans [4][5].

Critics, including researchers who study the Ecuadorian Laron cohort, caution against over-generalizing developmental IGF-1 deficiency (present from birth, shaping the whole growth trajectory) to interventions started in already-aged adults, since the biological context differs substantially, and note that GH/IGF-1 replacement therapy for legitimate deficiency in adults has established, different risk-benefit profiles than the cancer-protective effect seen in lifelong-deficient Laron patients [2]. The 2023 hallmarks-of-aging update lists deregulated nutrient-sensing, which includes insulin/IGF-1 signaling alongside mTOR and AMPK, as one of its core mechanistic categories [6].

The plain takeaway: reduced insulin/IGF-1 signaling is one of the best cross-species-validated longevity pathways in biology, but translating lifelong genetic deficiency findings into a safe adult intervention remains unresolved.