Why we measure it

The clinical interest in IGF-1 is shaped by a non-linear relationship with health outcomes: both extremes appear adverse. Very low IGF-1 is associated with sarcopenia, reduced bone density, increased cardiovascular risk, insulin resistance, and all-cause mortality — reflecting inadequate GH axis activity and anabolic drive. But very high IGF-1, particularly when chronically elevated, has been associated with increased risk of prostate, premenopausal breast, and colorectal cancers in epidemiological studies. A large systematic review and meta-analysis by Renehan et al., published in The Lancet, pooled data from prospective studies and found that higher circulating IGF-1 was associated with increased risk of several common cancers. However, within the normal population range — which is what Blueprint testing is designed to assess — the dominant concern is declining IGF-1 as a driver of age-related muscle loss, metabolic dysfunction, and functional decline. The GH/IGF-1 axis is acutely sensitive to lifestyle: deep sleep is the primary stimulus for nocturnal GH secretion; resistance training is the most potent exercise stimulus for IGF-1; and protein intake and caloric balance directly modulate hepatic IGF-1 production. Regular measurement makes this sensitivity actionable — allowing tracking of whether specific lifestyle interventions are producing a measurable endocrine response.

Why every 6 months

Unlike testosterone, IGF-1 does not exhibit a strong diurnal rhythm and is relatively stable across the day, though it responds to acute fasting and is best measured in a consistent, non-exhausted state. The six-month interval is appropriate for detecting the slow, clinically meaningful trajectory of IGF-1 across the adult lifespan — the gradual decline that correlates with accelerating sarcopenia in middle age — and for assessing the hormonal response to lifestyle interventions. The index responds measurably to changes in sleep quality, resistance training load, and protein intake within 8–12 weeks, meaning six-monthly testing provides sufficient resolution to confirm a meaningful change while avoiding the noise of week-to-week fluctuations.

What movement means

IGF-1 reference ranges are strongly age-dependent: concentrations that are normal for a 25-year-old are elevated for a 70-year-old. Each laboratory reports reference ranges stratified by age and sex, derived from assay-specific normative data. General adult values in middle age (40–60 years) typically fall between approximately 75 and 200 ng/mL, depending on the assay and reference population, with a progressive age-related decline thereafter. The clinically important distinction is not a single threshold but the position of an individual's result relative to the age-appropriate reference range — and the direction of change across draws. A level persistently at the lower quartile for age, and declining, warrants review of GH axis function and assessment of the modifiable lifestyle factors that are the most effective non-pharmacological levers for supporting this axis.

In the protocol