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Kidney Function

Cystatin C

Cystatin C is a small protein produced at a steady rate by every nucleated cell in the body, filtered freely by the kidneys, and reabsorbed in the proximal tubule. Because its production isn't influenced by muscle mass, age, sex, or diet to the same extent as creatinine, it's a more sensitive marker of early kidney function decline. In the UK Biobank biological age study (Nature Communications Biology, 2023), cystatin C emerged as the single strongest blood-based predictor of biological age across 25 markers tested.

Optimal Ranges

Clinical (NHS) Range

0.55-1.15 mg/L

mg/L

Performance-Optimised Range

<0.85 mg/L

mg/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 Cystatin C matters for performance

Creatinine — the standard NHS kidney marker — is muscle-dependent. A lean older adult can have creatinine in the normal range while their kidney function is silently declining; a heavily muscled athlete can show 'high' creatinine without any kidney issue. Cystatin C resolves this ambiguity. It's also one of the earliest signals of kidney function decline, often rising before creatinine does. For longevity scoring, cystatin C is the cleanest single marker of how well your filtration system is holding up — and filtration capacity is one of the most reliable correlates of biological age.

Symptoms

Signs your levels may be off

Low / Deficiency

  • Low cystatin C is not clinically meaningful
  • Levels below the reference range usually reflect lab variation rather than disease

High / Excess

  • Often asymptomatic in early stages — kidney function declines silently
  • Fatigue and reduced exercise tolerance (later)
  • Ankle swelling or puffy eyelids (advanced)
  • Higher blood pressure (advanced)
  • Pale skin (anaemia of chronic kidney disease)

Dietary Sources

Foods that support Cystatin C levels

Cystatin C is produced internally — diet supports the kidney environment, not the marker itselfAdequate hydration (target pale-straw urine)Moderate protein intake — 1.0-1.6 g/kg/day for most adultsOmega-3 fish (salmon, mackerel, sardines) for kidney inflammation controlBerries and dark leafy greens for endothelial protectionLimit ultra-processed food and added sugar (both elevate kidney workload)

Supplementation

Evidence-based supplementation

If cystatin C is creeping up, address the modifiable drivers first: blood pressure (target <120/75), HbA1c (target <40 mmol/mol), waist circumference, and NSAID use (chronic ibuprofen damages kidneys). Omega-3 (2-3 g EPA+DHA daily) has evidence for kidney inflammation control. Consider asking your GP for an eGFR-cystatin (rather than eGFR-creatinine) calculation if there's any concern — most UK labs can run it on the same sample.

Research

Key study

Biological age estimation using circulating blood biomarkers from UK Biobank

Bortz J, Guariglia A, Klaric L, et al.

Communications Biology (2023)

DOI: 10.1038/s42003-023-05456-z

Related Biomarkers

Organ Function

Creatinine & eGFR (Kidney Function)

Optimal: Creatinine: 70-110 µmol/L, eGFR: >90 mL/min/1.73m²

Metabolic

HbA1c (Glycated Haemoglobin)

Optimal: 20-34 mmol/mol (below 5.4%)

Inflammation

hs-CRP (High-Sensitivity C-Reactive Protein)

Optimal: Below 1.0 mg/L

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This 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.