Does thyroid hormone affect insulin-like growth factor‑1 (IGF‑1) levels?

Medical Advisory BoardAll articles are reviewed for accuracy by our Medical Advisory Board
Educational purpose only • Exercise caution as content is pending human review
Article Review Status
Submitted
Under Review
Approved

Last updated: March 20, 2026 • View editorial policy

Have a follow-up question?

Our Medical A.I. is used by practicing medical doctors at top research institutions around the world. Ask any follow up question and get world-class guideline-backed answers instantly.

Ask Question

Does Thyroid Hormone Influence IGF-1?

Yes, thyroid hormone directly modulates IGF-1 and IGFBP-3 levels independently of growth hormone, with hypothyroidism lowering IGF-1 concentrations and hyperthyroidism initially raising them, though these effects are modified by nutritional status and energy balance. 1, 2

Mechanism of Thyroid Hormone Effects on IGF-1

Thyroid hormones act at multiple levels of the GH-IGF-I axis, from hypothalamic control of GH release through tissue expression of IGF-I and its binding proteins. 3 The relationship is complex and bidirectional:

  • Thyroid hormones modulate IGF-1 and IGFBP-3 synthesis and secretion without requiring GH mediation, as demonstrated in patients with autoimmune thyroid disease where GH levels remained unchanged despite significant alterations in IGF-1 and IGFBP-3. 2

  • IGFBP-3 levels show a significant positive correlation with free T4 and free T3 concentrations, indicating a direct dose-response relationship between thyroid hormone levels and IGF binding protein expression. 2

Clinical Effects by Thyroid Status

Hypothyroidism

  • Hypothyroid patients exhibit significantly reduced IGF-1 (161.5 ± 13.1 µg/L vs. 217.9 ± 20.3 µg/L in controls) and IGFBP-3 (3.2 ± 0.3 mg/L vs. 4.2 ± 0.3 mg/L in controls). 1

  • Levothyroxine replacement therapy does not significantly restore IGF-1 or IGFBP-3 levels to normal, suggesting that achieving euthyroid status alone may be insufficient to normalize the IGF axis. 1

  • IGFBP-1 is paradoxically elevated in hypothyroidism (15.5 ± 0.9 µg/L vs. 5.7 ± 1.5 µg/L in controls) and decreases with treatment (to 8.8 ± 1.4 µg/L). 1

  • Severe hypothyroidism can produce falsely low IGF-1 levels even in the presence of GH excess, which is a critical diagnostic pitfall when evaluating for acromegaly or GH deficiency. 4

Hyperthyroidism

  • Hyperthyroid patients initially show IGF-1 levels similar to or higher than controls (198.8 ± 17.0 µg/L baseline, rising to 305.4 median in Graves' disease), but these levels significantly decrease after achieving euthyroid status (to 156.6 ± 11.1 µg/L). 1, 5

  • IGFBP-3 levels are elevated in hyperthyroidism (4.2 ± 0.2 mg/L) and decrease significantly with treatment (to 3.3 ± 0.1 mg/L). 1

  • IGFBP-1 is markedly elevated in hyperthyroidism (22.7 ± 2.6 µg/L) and falls with antithyroid therapy (to 11.0 ± 1.7 µg/L). 1

  • Serum IGF-1 concentrations show a negative association with log-transformed TSH (logTSH) in both hyperthyroid and euthyroid states, persisting even after adjustment for age and sex (β = -20.22 at baseline, β = -20.51 at 6 months). 5

Critical Confounding Factor: Nutritional Status

The effects of thyroid status on IGF-1 are substantially modified by food intake and energy balance, which has been ignored in many earlier studies. 6

  • Hypothyroid animals on controlled food intake and hyperthyroid animals receiving double food intake both showed the highest IGF-1 and insulin levels, despite opposite thyroid states. 6

  • GH levels were inversely related to IGF-1 in these nutritional contexts, with hypothyroids and hyperthyroids on extra food showing lower GH but higher IGF-1 than euthyroid controls. 6

  • Nutritional signals are capable of overriding the direct effects of thyroid status on circulating IGF-1, meaning that clinical interpretation must account for caloric intake and metabolic state. 6

Clinical Implications for Hormone Replacement

Thyroid Hormone Replacement Considerations

  • Before starting L-T4 therapy in central hypothyroidism, evaluate for adrenal insufficiency, as thyroid hormone can precipitate adrenal crisis by accelerating cortisol metabolism. 7

  • Target free T4 levels in the mid to upper half of the reference range with L-T4 doses averaging 1.6 µg/kg/day, adjusting based on clinical context and age. 7

  • Do not use TSH levels to adjust thyroid replacement in central hypothyroidism, as the pituitary feedback mechanism is disrupted. 7

Growth Hormone Replacement Interactions

  • Test HPA axis function before and after starting GH replacement in patients not receiving glucocorticoid replacement, as GH can unmask adrenal insufficiency. 7

  • When administering GH, titrate doses to maintain IGF-1 levels below the upper limit of normal, reducing the dose if side effects occur. 7

  • Monitor IGF-1 at least twice yearly during recombinant GH therapy, adjusting dosing to keep IGF-1 within the physiologic range for safety and growth prediction. 4

Diagnostic Pitfalls to Avoid

  • Never interpret IGF-1 in isolation when evaluating thyroid dysfunction; severe hypothyroidism can falsely lower IGF-1 even in GH excess states, while uncontrolled diabetes and hepatic/renal failure can falsely elevate it. 4

  • Use age-, sex-, and Tanner-stage-specific reference ranges for IGF-1, as marginal elevations during adolescent growth spurts require cautious interpretation. 4

  • Recognize that achieving biochemical euthyroidism may not immediately normalize IGF-1 levels, particularly in hypothyroidism where replacement therapy shows limited effect on IGF-1 restoration. 1

  • Account for nutritional status and energy balance when interpreting IGF-1 changes in thyroid dysfunction, as caloric intake can override direct thyroid hormone effects. 6

  • Apply assay-specific reference ranges for IGF-1 measurements, as inter-assay variability is substantial and can lead to misinterpretation if ignored. 4

References

3
Research

Influence of thyroid hormones on the GH-IGF-I axis.

Trends in endocrinology and metabolism: TEM, 1993

4
Guideline

IGF‑1 as a Biomarker for Growth Hormone Excess and Anabolic Status

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

Related Questions

Should patients with systemic lupus erythematosus be prescribed low‑dose aspirin and atorvastatin?
What is the most appropriate ADHD medication for an adult kidney donor who wants to avoid the blood‑pressure‑raising effects of amphetamines?
Which antibiotics are associated with vaginal yeast infections?
What is the appropriate management for a child bitten by an unknown dog with uncertain rabies vaccination status?
What is the recommended management for a 17 mm low‑attenuation left adnexal mass in an 80‑year‑old woman?
How should I manage a patient with elevated intact parathyroid hormone (109 pg/mL) despite normal serum calcium (9.0 mg/dL) and adequate 25‑hydroxyvitamin D (31 ng/mL)?

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.