Not all biomarkers are equal. Some are well-validated predictors of health outcomes with decades of evidence behind them. Others are newer, more expensive, and still being characterised. A practical approach starts with what's most established and works outward from there.

HbA1c — glycated haemoglobin — is one of the most powerful single markers available, reflecting average blood glucose over the previous three months. It sits at the centre of metabolic health, which is itself central to most major age-related diseases. Elevated HbA1c predicts cardiovascular disease, dementia, kidney disease, and all-cause mortality with consistent strength across populations. It's measured in a standard blood test, costs nothing on the NHS if you have relevant risk factors, and responds relatively quickly to dietary and exercise changes. For most people over 50, this is the first number to know.

hs-CRP (high-sensitivity C-reactive protein) is the most accessible marker of systemic inflammation — the chronic, low-grade inflammatory state that underlies cardiovascular disease, neurodegeneration, and accelerated cellular ageing. A reading below 1mg/L is optimal; above 3mg/L signals meaningfully elevated inflammatory load. It's affected by acute illness and should be interpreted as a trend rather than a single reading. The drivers of elevated hs-CRP — poor diet, visceral fat, inadequate sleep, sedentary behaviour, chronic stress — are the same things that accelerate biological ageing through every other pathway.

Fasting insulin is arguably more informative than fasting glucose for early metabolic dysfunction. Glucose can remain normal for years while insulin is rising — a sign that the pancreas is working harder than it should to maintain blood sugar control. Elevated fasting insulin is an early warning of insulin resistance and predicts cardiovascular disease, type 2 diabetes, and cognitive decline with considerable lead time. It's not routinely tested on the NHS but is available privately and worth requesting if metabolic health is a concern.

Vitamin D is less a longevity marker than a baseline check, but deficiency is so common — particularly in the UK — and so consistently associated with immune dysfunction, depression, muscle weakness, and accelerated ageing that knowing your level is simply responsible. The optimal range is broadly 75–150 nmol/L; most UK adults in winter are well below this without supplementation.

Lipid profile — total cholesterol, LDL, HDL, and triglycerides — remains the standard cardiovascular risk assessment and is worth understanding beyond the headline total cholesterol number. Triglycerides and HDL are more informative than LDL alone for metabolic health: a triglyceride-to-HDL ratio above 3 is a stronger predictor of insulin resistance and cardiovascular risk than LDL in many populations. If your GP only gives you a total cholesterol figure, ask for the breakdown.

VO2 max — maximum oxygen uptake — is the most powerful single predictor of all-cause mortality that can be measured outside a laboratory. A large study of over 120,000 people found that low cardiorespiratory fitness was associated with a higher mortality risk than smoking, hypertension, or diabetes. It can be estimated from a standard submaximal exercise test or from fitness tracker data, though lab testing is more accurate. More importantly, it's highly responsive to training — specifically, a combination of moderate aerobic work and high-intensity intervals.

Grip strength is a deceptively simple measure with remarkable predictive power. A 2015 meta-analysis of nearly 200,000 people found that grip strength was a stronger predictor of cardiovascular mortality than blood pressure. It reflects overall musculoskeletal integrity, neural efficiency, and lean mass — all of which decline with age and all of which respond to resistance training. A dynamometer test takes thirty seconds and costs almost nothing.