Insulin-like Growth Factor 1

Hormones marker

IGF-1

Insulin-like Growth Factor 1

Category: Hormones
Unit: nmol/L

Growth factor produced primarily by the liver in response to growth hormone (GH). Reflects overall GH secretion and mediates many of GH's anabolic effects. Age- and sex-specific reference ranges apply.

PED Notes

CRITICAL marker for GH use monitoring. Exogenous GH directly elevates IGF-1 — the primary way to confirm GH is working and dose-response. Supraphysiological IGF-1 (>1.5x upper limit) indicates high GH dosing and increases risk of insulin resistance, soft tissue growth, and long-term cancer risk. AAS alone do not significantly affect IGF-1. Insulin co-administration with GH further amplifies IGF-1 levels. Target for health-conscious GH use: upper-normal range (25-35 nmol/L). Recheck 4-6 weeks after dose changes. Fasting state and time since last GH injection affect levels.

When elevated on exogenous GH (dose management):

  • Target range for health-conscious GH use: 25-35 nmol/L (upper-normal)
  • IGF-1 >40 nmol/L: consider reducing GH dose by 0.5-1 IU/day
  • IGF-1 >50 nmol/L: reduce GH dose immediately -- significantly elevated cancer and metabolic risk
  • Recheck IGF-1 4-6 weeks after any GH dose change (takes time to stabilise)
  • Blood draw timing: ideally 12-24h after last GH injection for stable reading; avoid testing within 4h of injection

Risks of chronically high IGF-1 (>1.5x upper limit):

  • Insulin resistance and impaired glucose tolerance (synergistic with GH)
  • Acromegalic features: soft tissue growth (hands, feet, jaw, nose, internal organs)
  • Increased cancer risk (IGF-1 is a potent growth signal -- promotes cell proliferation)
  • Cardiomegaly (heart enlargement) with prolonged supraphysiological levels
  • Visceral organ growth (intestinal, cardiac) -- contributes to "GH gut" at high doses

GH dose guidelines by goal:

  • Anti-ageing/recovery: 1-2 IU/day (IGF-1 typically stays within normal range)
  • Body composition/fat loss: 2-4 IU/day (IGF-1 upper-normal to mildly elevated)
  • Bodybuilding/muscle growth: 4-8+ IU/day (IGF-1 often significantly elevated -- monitor closely)

Supplements/Lifestyle (to manage elevated IGF-1 side effects):

  • Berberine -- 500mg 2-3x/day (improves insulin sensitivity, may modestly reduce IGF-1)
  • Metformin -- 500-1000mg/day (addresses GH-induced insulin resistance; may reduce IGF-1 slightly)
  • Monitor fasting glucose and HbA1c alongside IGF-1
  • If fasting glucose >5.5 mmol/L on GH, reduce dose or add Berberine/Metformin

When IGF-1 is LOW (off GH):

  • Low IGF-1 off exogenous GH may indicate: poor nutrition, liver dysfunction (IGF-1 is hepatic), growth hormone deficiency, or chronic illness
  • Ensure adequate protein intake (IGF-1 production requires amino acid substrate)
  • Optimise sleep (GH pulses occur during deep sleep)
  • Address any liver dysfunction (liver produces >75% of circulating IGF-1)

References:

  • Dong, H., Zhao, Y., Zhao, L., & Lu, F. (2013). The effects of berberine on blood lipids: A systemic review and meta-analysis. Planta Medica, 79(6), 437-446. DOI: 10.1055/s-0032-1328321
  • Guo, J., Chen, H., Zhang, X., et al. (2021). The effect of berberine on metabolic profiles in type 2 diabetic patients. Oxidative Medicine and Cellular Longevity, 2021, 2074610. DOI: 10.1155/2021/2074610
  • UK Prospective Diabetes Study Group. (1998). Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). The Lancet, 352(9131), 854-865. DOI: 10.1016/S0140-6736(98)07037-8

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Frequently Asked Questions

Reference Ranges

Standard Range

11 - 31 nmol/L

VitalMetrics Range

11 - 45 nmol/L

Statistics