IGF-1: what it says about your growth hormone axis

Why IGF-1 instead of growth hormone

The pituitary releases growth hormone in bursts, mostly at night, and levels between bursts can be near undetectable in a perfectly healthy person. Draw GH at ten in the morning and you have measured the gap between pulses.

Insulin-like growth factor 1 is produced in response to GH, largely by the liver, and circulates bound to binding proteins that keep it comparatively steady through the day. That stability is why clinical practice uses IGF-1 to assess the axis, and why endocrine guidelines rely on it for both deficiency and excess.

What a low or high value can mean

IGF-1 sits downstream of several things, so a single value does not identify which one is responsible.

• Low: reduced GH secretion, but also poor nutrition or insufficient calorie and protein intake, liver disease, poorly controlled diabetes, hypothyroidism, or systemic illness. Nutritional status is a genuinely common explanation.
• High: increased GH secretion, and in the clinical setting the concern is acromegaly, which is diagnosed with confirmatory testing rather than an IGF-1 alone.
• Mid-range and age-appropriate: usually unremarkable, and worth leaving alone.

Why higher is not the goal

This is the part that is easy to get wrong. IGF-1 is a growth signal, and growth signaling is not uniformly beneficial.

Observational research has associated higher IGF-1 with increased incidence of certain cancers, including prostate, breast and colorectal, while lower IGF-1 has been associated with frailty, reduced muscle mass and cardiovascular outcomes in older adults. Several analyses describe a U-shaped relationship with mortality, where both tails look worse than the middle.

These are associations from observational data, and they do not establish that moving your IGF-1 in either direction changes your outcome. What they do establish is that treating a higher number as an achievement is not supported. The clinical goal is an appropriate value for your age, not a maximal one.

IGF-1 and growth hormone peptides

Sermorelin, tesamorelin, CJC-1295 and ipamorelin all aim at increasing your own GH release, which raises IGF-1 downstream. That is the intended mechanism.

It is also why we strongly recommend IGF-1 before starting and again during therapy: the point is to confirm the axis is responding and to confirm it is not being pushed outside an age-appropriate range. Providers screen the relevant history before prescribing in this class, including active or historical malignancy, and that screening is a prescriber's responsibility rather than a checkbox on an intake form.

This is also why a GH peptide belongs alongside an IGF-1 measurement rather than on its own. Measuring the axis is what turns a compound into a protocol, and it is how our providers decide whether to continue, adjust or stop.

Practical testing notes

IGF-1 assays differ between laboratories and results are best expressed as an age and sex adjusted standard deviation score, or at least read against that laboratory's own age-matched range. Track it at the same laboratory where you can.

Be aware that a recent period of significant under-eating, an acute illness, or an unusually stressful stretch can pull the value down and does not necessarily mean anything about your pituitary.

References

1. Molitch et al., evaluation and treatment of adult growth hormone deficiency, Endocrine Society clinical practice guideline
2. Katznelson et al., acromegaly, Endocrine Society clinical practice guideline
3. Burgers et al., meta-analysis of IGF-1 and mortality, Journal of Clinical Endocrinology and Metabolism, 2011
4. Endogenous Hormones and Breast Cancer Collaborative Group and related IGF-1 cohort analyses, The Lancet Oncology
5. Biomarker hub: Hormonal biomarkers
6. Peptide guides: Sermorelin, tesamorelin, CJC-1295 and ipamorelin compared