HbA1c (Glycated Haemoglobin)

What it is

Glucose covalently attaches to haemoglobin in red blood cells; the percentage of glycated haemoglobin (HbA1c) reflects the average plasma glucose over the prior ~3 months (the red-cell lifespan).

Reference ranges

• Normal: <5.7% (<39 mmol/mol)
• Pre-diabetes: 5.7–6.4% (39–47 mmol/mol)
• Diabetes: ≥6.5% (≥48 mmol/mol)

For longevity-oriented targets, many practitioners aim for <5.5% in metabolically healthy adults, with the caveat that haemoglobinopathies and red-cell-lifespan variations distort the test.

Why it matters for longevity

• Strongly predicts cardiovascular events independent of overt diabetes.
• Higher HbA1c in midlife tracks dementia risk in long-term cohorts.
• Glycation of structural proteins (collagen, lens crystallins, neuronal proteins) accumulates with sustained hyperglycaemia — an “aging from glucose” mechanism.

What lowers HbA1c

• Weight loss.
• Carbohydrate quality (less refined; more fibre).
• Exercise, particularly resistance + aerobic.
• Metformin, SGLT2 inhibitors, GLP-1 agonists.
• Acarbose targets post-prandial spike.

Related entries

Type 2 diabetes, Fasting insulin / HOMA-IR, Mediterranean diet.