What is HbA1c?
Glycated hemoglobin
HbA1c is a blood test that shows your average blood sugar over roughly the past three months.
Think of your red blood cells as white T-shirts that slowly get stained by sugar in the blood. They live about three months, so the amount of staining tells you how much sugar they've been soaking in over that time.
Why it matters for aging
Sugar in your blood sticks to hemoglobin, the oxygen-carrying protein in red blood cells. The higher your average blood sugar, the more hemoglobin gets "sugar-coated". The test measures that percentage.
In the US, an HbA1c below 5.7 percent is considered normal, 5.7 to 6.4 percent indicates prediabetes, and 6.5 percent or higher indicates diabetes. Some conditions, like anemia, can make the result less accurate, so doctors sometimes combine it with other tests.
A common myth
A normal HbA1c means your metabolism is perfectly healthy.
HbA1c is a great measure of average blood sugar, but insulin resistance can build for years before it rises, because the body compensates with extra insulin. A normal result is reassuring, not a full all-clear.
Go deeper
Deep dives
- Early signs of insulin resistance, and what comes before them
- Berberine vs metformin: what the evidence actually says
- Why am I always tired after 40? The upstream answer
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Updated Nov 9, 2026 · All terms