HbA1c & Metabolic Health
Why fasting glucose isn't enough, and how HbA1c provides a 90-day window into your metabolic state.
Hemoglobin A1c (HbA1c) measures the percentage of red blood cells that have sugar attached to them. Because red blood cells live for approximately 3 months, this test provides a reliable average of your blood sugar levels over the past 90 days. It is a far more robust metric than a single fasting glucose reading, which can fluctuate based on acute stress, sleep, or yesterday's meals.
Clinical vs. Optimal Ranges
The standard medical reference ranges for HbA1c are designed to diagnose pathology (diabetes), not to define optimal health or longevity.
| Category | Clinical Range | Optimal (Longevity) |
|---|---|---|
| Normal | < 5.7% | 4.6% - 5.2% |
| Prediabetes | 5.7% - 6.4% | Avoid |
| Diabetes | ≥ 6.5% | Avoid |
Common Mistakes in Testing
- Ignoring Red Blood Cell Turnover: If you have anemia or conditions that alter red blood cell lifespan, HbA1c can be artificially high or low.
- Relying on HbA1c Alone: It must be viewed alongside Lipid Panels and Fasting Insulin (HOMA-IR) for a complete metabolic picture.
- Testing Too Frequently: Because it reflects a 90-day average, testing more often than every 3 months provides little actionable data.
Frequently Asked Questions
How does HbA1c relate to continuous glucose monitoring (CGM)?
A CGM provides real-time data on glycemic variability (spikes and crashes), while HbA1c provides the long-term average. Both are necessary. You can have a "normal" HbA1c but high variability, which is damaging to vascular endothelium.
Can exercise lower HbA1c?
Yes. Zone 2 cardio improves mitochondrial efficiency, while resistance training increases muscle mass (the body's largest glucose sink). Improving VO2 Max directly correlates with better metabolic control.