HbA1c

HbA1c is hemoglobin with sugar attached — a measurement of how much glucose has glycated red blood cells over the previous ~3 months. It is the standard biomarker for long-term blood sugar control, but longevity-optimal targets are tighter than standard clinical cutoffs.

Red blood cells have a lifespan of approximately 120 days. During that time, glucose in the bloodstream non-enzymatically attaches to hemoglobin — the same glycation process that produces Advanced Glycation End-products in tissues. HbA1c measures the percentage of hemoglobin that has been glycated, providing a weighted average of blood glucose exposure over the preceding 2–3 months.

Standard clinical cutoffs are: normal below 5.7%, pre-diabetes 5.7–6.4%, diabetes above 6.5%. Longevity-oriented practice uses tighter targets: optimal is below 5.4%, with any value above 5.3% worth attention. The reason for the tighter target is that the association between HbA1c and biological aging is continuous, not binary — even values in the "normal" range correlate with rising cardiovascular and cognitive risk.

HbA1c has limitations. It is affected by anything that alters red blood cell lifespan: anemia shortens RBC lifespan and falsely lowers HbA1c; hemolytic conditions do the same. Conversely, conditions that extend RBC lifespan falsely elevate it. In women with very low ferritin or ongoing menstrual blood loss, HbA1c may underestimate true glucose exposure — making fasting glucose, fasting insulin, and postprandial glucose monitoring (CGM) useful complements.

The levers for lowering HbA1c are well-established: Zone 2 aerobic exercise (improves muscle GLUT4 and insulin sensitivity), strength training (increases muscle glucose storage capacity), post-meal walks (activate contraction-mediated glucose uptake), time-restricted eating, reducing refined carbohydrates and liquid sugar, and sleep optimization. A combined intervention protocol typically reduces HbA1c by 0.3–0.8% within 3–4 months.

For women in perimenopause, HbA1c often drifts upward as estrogen declines and visceral adiposity rises — making it a key biomarker to track through the hormonal transition.

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