Glycated Hemoglobin and Long-Term Sugar Exposure
Glucose in the bloodstream spontaneously attaches to hemoglobin proteins through a non-enzymatic process called glycation. The higher the average blood sugar over the lifespan of a red blood cell (90-120 days), the greater the percentage of hemoglobin molecules that become glycated. This same glycation process damages proteins throughout the body, including in blood vessels, kidneys, nerves, and eyes, which is how chronic hyperglycemia causes diabetic complications.
Limitations
HbA1c can be falsely low or high in conditions affecting red blood cell lifespan (anemia, blood loss, hemoglobin variants). It also does not capture glucose variability.
A Lagging Indicator
By the time HbA1c reaches 5.7% (prediabetes), insulin resistance has typically been present for many years. It is a late, not early, marker.
Optimal HbA1c Benchmarks
Common Questions
What is a good HbA1c level?
While the standard cutoff for normal is below 5.7%, optimal health experts recommend targeting below 5.2% for the lowest long-term disease risk.
How quickly can HbA1c change?
Because it reflects a 90-day average, meaningful changes take 2-3 months to appear. This is why retesting more frequently than every 3 months is not useful.