Optimal Ranges
Clinical (NHS) Range
10–36 nmol/L (age-dependent — declines ~14% per decade after 30)
nmol/L
Performance-Optimised Range
18–28 nmol/L (mid-range, balancing anabolic benefit and longevity risk)
nmol/L
The clinical range defines what is considered medically “normal” — broad enough to cover 95% of the population. The performance range reflects where research and clinical experience suggest most people feel and function at their best.
Why It Matters
Why IGF-1 matters for performance
IGF-1 sits at the intersection of performance and longevity — and the optimal range is a deliberate trade-off. Higher IGF-1 (within range) supports muscle growth, recovery, bone density, and cognitive function. But persistently elevated IGF-1 above the reference range is associated with increased cancer risk in epidemiological studies, because the same growth-promoting signals that repair tissue also accelerate tumour cell proliferation. For active adults, the goal is a healthy mid-range IGF-1: high enough to support recovery and lean mass, low enough to avoid excess proliferative signalling. Low IGF-1 in younger adults often signals poor protein intake, chronic caloric restriction, liver dysfunction, or growth hormone deficiency — all of which impair recovery and accelerate sarcopenia.
Symptoms
Signs your levels may be off
Low / Deficiency
- Reduced muscle mass and slow recovery from training
- Increased body fat, particularly visceral
- Poor wound healing and slow tissue repair
- Low bone density and increased fracture risk
- Fatigue and reduced exercise tolerance
- Cognitive decline and poor memory
- Thin skin and premature ageing
High / Excess
- Acromegaly features (enlarged hands, feet, jaw — if GH-driven)
- Joint pain and stiffness
- Increased risk of colorectal, breast, and prostate cancer (epidemiological association)
- Skin tags and thickened skin
- Insulin resistance (IGF-1 and insulin share receptor cross-talk)
Dietary Sources
Foods that support IGF-1 levels
Supplementation
Evidence-based supplementation
IGF-1 is not directly supplemented over the counter. It is modulated through lifestyle: adequate protein intake (1.6–2.2 g/kg/day), sufficient calories to avoid chronic energy deficit, quality sleep (7–9 hours — growth hormone is released primarily during slow-wave sleep), and resistance training (heavy compound movements transiently increase GH secretion). Zinc deficiency directly suppresses IGF-1 — supplement 15–30 mg/day if serum zinc is low. Vitamin D deficiency is also associated with lower IGF-1 levels. Intermittent fasting transiently suppresses IGF-1 (this is part of the proposed longevity mechanism of fasting, but may be counterproductive for muscle preservation). If IGF-1 is persistently below range despite adequate nutrition, a GP referral for GH stimulation testing is warranted — adult growth hormone deficiency is underdiagnosed and treatable. Conversely, if IGF-1 is persistently above range, investigation for acromegaly is essential. Retest at 90 days after any lifestyle change, fasted morning draw preferred.
Research
Key study
Serum insulin-like growth factor I and risk of cancer: results from the EPIC study
Rinaldi S, Cleveland R, Norat T, et al.
International Journal of Cancer (2010)
DOI: 10.1002/ijc.25007Related Biomarkers
Related Guides
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Order Your TestThis content is for educational purposes only and does not constitute medical advice. Your data suggests areas for optimisation, but any concerns should be discussed with a qualified healthcare professional. If your results flag values outside safe ranges, we recommend consulting your GP.