HbA1c (hemoglobin A1c) measures the percentage of your red blood cells that have sugar stuck to them. Because red blood cells live about three months, HbA1c gives you a rolling average of your blood sugar over that time. It's how doctors diagnose prediabetes and diabetes, and unlike a fasting glucose test, no fasting is needed.
What does HbA1c measure?
When sugar floats through your bloodstream, some of it attaches to hemoglobin, the protein inside red blood cells that carries oxygen. The more sugar in your blood, the more hemoglobin gets coated. HbA1c reports that coating as a percentage.
A single blood sugar reading is a snapshot of one moment. HbA1c is more like a three-month photograph. It captures the big picture, including spikes after meals, dips overnight, and everything in between.
What's a normal HbA1c level?
The ranges below are used by the American Diabetes Association to classify blood sugar control. A higher percentage means more sugar has been in your blood over the past three months.
HbA1c ranges
| HbA1c | Category | What it means |
|---|---|---|
| Below 5.7% | Normal | Blood sugar has been in a healthy range |
| 5.7 – 6.4% | Prediabetes | Blood sugar is higher than normal but not yet diabetes |
| 6.5% or higher | Diabetes | Blood sugar has been consistently elevated |
These thresholds are from the 2026 ADA Standards of Care. Each 1% in HbA1c corresponds to roughly a 30 mg/dL change in average blood sugar.
About 1 in 3 American adults have prediabetes, and most don't know it. A simple HbA1c test can tell you where you stand.
What does each 1% increase in HbA1c mean?
Higher HbA1c isn't just a number. It translates directly into higher risk for complications. Research shows that for each 1% rise in HbA1c, cardiovascular risk increases by roughly 15–18%.
HbA1c and estimated average blood sugar
| HbA1c | Estimated average blood sugar | Risk level |
|---|---|---|
| 5.0% | 97 mg/dL | Normal |
| 5.7% | 117 mg/dL | Prediabetes threshold |
| 6.0% | 126 mg/dL | Prediabetes |
| 6.5% | 140 mg/dL | Diabetes threshold |
| 7.0% | 154 mg/dL | Diabetes |
| 8.0% | 183 mg/dL | Higher risk of complications |
Estimates based on the ADAG study formula. Individual variation exists.
Why does blood sugar matter for your heart?
This is the connection many people miss. Diabetes doubles your risk of heart disease and stroke. Even prediabetes raises cardiovascular risk. High blood sugar damages the lining of your arteries over time, triggers inflammation, and makes plaque build up faster.
People with diabetes also tend to have higher triglycerides, lower HDL cholesterol, and smaller, denser LDL particles. All of these accelerate plaque growth. That's why managing blood sugar is heart care, not just diabetes care.
Heart risk
2x
Diabetes roughly doubles your risk of cardiovascular disease, even after accounting for other risk factors like cholesterol and blood pressure.
What's the advantage over a fasting glucose test?
Fasting glucose requires you to skip food for 8–12 hours before a blood draw. HbA1c doesn't. You can test it any time of day, after eating, and it's just as accurate. It also captures your average over months, while fasting glucose only shows what your blood sugar was that morning.
That said, no single test tells the whole story. A fasting glucose test can catch spikes that HbA1c might average out, and a CGM (continuous glucose monitor) shows your blood sugar patterns in real time. Together, they give a fuller picture.
How can you lower your HbA1c?
The good news: HbA1c responds well to lifestyle changes. Most people who make consistent changes see improvement within two to three months. Here are the strategies with the strongest evidence.
What works to lower HbA1c
| Strategy | Typical HbA1c reduction | Details |
|---|---|---|
| Reduce refined carbs and sugar | 0.3 – 1.0% | Cutting processed carbs and added sugar has the most direct effect. A Mediterranean-style diet is one of the best-studied patterns. |
| Exercise regularly | 0.3 – 0.7% | 150 min/week of moderate activity plus resistance training. Walking 15–30 minutes after meals is especially effective because muscles pull sugar from your blood. |
| Lose 5–10% of body weight | 0.3 – 1.0% | Even modest weight loss significantly improves insulin sensitivity. People who lose 5–10% of body weight are three times as likely to lower HbA1c by 0.5%. |
| Improve sleep | Supportive | Poor sleep worsens insulin sensitivity. Aim for 7–8 hours per night. |
Reductions are approximate and based on published trials. Results vary. Combining strategies produces the best outcomes.
What about medication?
When lifestyle changes aren't enough, medication can help. Metformin is the most common first-line drug for type 2 diabetes. It's effective, inexpensive, doesn't cause weight gain, and reduces cardiovascular risk. Your doctor may also recommend newer medications like GLP-1 receptor agonists, which lower blood sugar and support weight loss.
For people with prediabetes, the ADA recommends considering metformin especially if you're under 60, have a BMI of 35 or above, or have an HbA1c of 6.0% or higher. But for most people with prediabetes, lifestyle changes alone are the first step.
The bottom line
HbA1c is one of the simplest, most useful blood tests you can get. It tells you where your blood sugar has been over the past three months, no fasting required. If your number is above 5.7%, you have a clear path to bring it down. And because blood sugar directly affects your arteries, improving your HbA1c is one of the most powerful things you can do for your heart.
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