High A1C Levels Can Lead to Heart Disease — Here’s Why You Should Get Tested

You need a certain amount of sugar (glucose) in the blood to fuel all the cells of the body. But blood glucose can cause problems when it gets too high. This includes a greater risk of cardiovascular disease.

A test called hemoglobin A1C (HbA1C or A1C) can give you an idea of your average blood glucose level over the past 2 to 3 months. It measures the amount of glucose that gets stuck to hemoglobin, a protein in your blood cells. A1C levels are higher in people with prediabetes or diabetes.

Diabetes can lead to a number of complications, including heart disease. But it’s important to know that a high A1C — even without a diagnosis of diabetes — can increase the risk as well. Here, we’ll explore the link between a high A1C and heart disease.

What is a normal A1C level?

A normal A1C level is 5.6% or below. It’s important to note that A1C is different from a blood glucose test, which measures the amount of glucose (sugar) in your blood at the moment of testing.

Here is a quick breakdown of A1C categories:

• Normal: 5.6% or less

• Prediabetes: 5.7% to 6.4%

• Diabetes: 6.5% or higher

What happens if your A1C is too high?

When A1C is high, it’s likely that glucose isn’t just sticking to your hemoglobin — it’s starting to stick to other cell types, too. This can damage your nerves, eyes, and even your heart.

Some of the complications of a high A1C level over the long term are the same as those in diabetes. These complications include:

• Retinopathy: The small blood vessels in the eyes can become damaged and lead to blindness.

• Neuropathy: High glucose over a long period of time can damage the nerves. You may feel this as numbness, tingling, or pain — especially in the feet.

• Chronic kidney disease: If high levels of glucose damage the blood vessels in the kidneys, they can no longer work properly. This can lead to kidney failure and the need for dialysis.

• Stroke: The brain depends on a healthy blood supply for oxygen and nutrients. If the vessels to the brain are damaged, the blood supply can be cut off. This can lead to a stroke.

• Heart attack: The heart also relies on good blood supply to function properly. If the arteries to the heart are blocked, you can have a heart attack.

• Foot ulcers: The feet are common places for wounds due to neuropathy and lower blood flow. And damage to blood vessels in the feet from high glucose makes it harder to heal infections and wounds.

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High A1C and cardiovascular risk

Medical experts know that diabetes and prediabetes increase the risk of heart disease. This is why it’s common for people with diabetes to see a cardiologist (heart specialist).

But even if you don’t have a diagnosis of diabetes or prediabetes, you may benefit from an A1C test. This is because a high A1C is linked to an increased risk for heart disease, even in people without diabetes. So this can be one way to get an understanding of your current risk. Experts recommend getting your A1C level checked at age 35 — or sooner if you have risk factors for diabetes.

The good news is that there are treatment and lifestyle options to help reduce your A1C and your risk for heart disease. The sooner you take steps to manage your health, the better. In many cases, it’s possible to prevent further health problems by acting on them early.

At what A1C level does risk increase?

Studies suggest an A1C level above 5.5% for men and above 6% for women can increase cardiovascular risk for people without diabetes. 

But the risk seems to be different for people with Type 2 diabetes. The American Diabetes Association recommends they keep their A1C below 7%. In terms of cardiovascular health, it's actually safer for people with diabetes to keep their A1C between 6% and 7%. That’s because research suggests there are greater risks with aggressively lowering their A1C. It’s not clear why this is, but it could be related to episodes of hypoglycemia with intense glucose lowering therapy.

What are the heart screening tests for people with a high A1C?

The heart tests for people with a high A1C are the same ones healthcare professionals use for routine heart screening. If your A1C is high, you may need to do these tests at an earlier age or more often than other people. Depending on the results, your primary care provider may refer you to a cardiologist.

Electrocardiogram (ECG/EKG)

An electrocardiogram (EKG or ECG) test is a safe and painless test that measures the electrical signals of your heart. An EKG shows if your heart is beating at a normal rate, rhythm, and strength.

An EKG can also show:

• Heart enlargement

• Signs of heart inflammation

• Prior heart damage

• Signs of a heart attack 

Coronary artery calcium scan (CAC)

This test is a CT scan that measures calcium in your coronary arteries (which supply blood to your heart muscle). The score can help determine risk of cardiovascular disease for people with high A1C, even without diabetes. But it’s not necessary for everyone, so ask your healthcare professional if it could be helpful for you.

Diagnostic tests

Depending on your EKG and/or CAC results, risk factors, and symptoms, you might need more testing. There are many tests healthcare professionals use to check heart function.

Here are some of the most common tests:

• Echocardiogram: An echocardiogram (echo) is a noninvasive test that uses sound waves to create moving pictures of your heart. The pictures show the size and shape of your heart and how well your heart is pumping blood. A Doppler ultrasound is a type of echo that shows how well blood flows through the heart’s chambers and valves.

• Stress test: A stress test shows how well your heart is able to handle the stress of its workload. This can be done with exercise or medication (pharmacologic). Either way, the test can detect if there’s enough blood flow through the arteries to your heart muscle.

• Stress echocardiogram: This combines the images of an echo with the stress test. Comparing before and after images can provide more information about how the heart responds to increased workload.

How can you lower your A1C level?

If you have an elevated A1C, the best way to prevent heart disease is to work on lowering your A1C. Since high blood glucose levels cause an increase in A1C, you’ll need to start by getting your blood sugar down. There are several ways to reduce blood sugar and A1C for better heart health.

Diet

Your healthcare team will likely suggest a heart-healthy diet. This includes more whole foods like fruit and vegetables. A heart-healthy diet will also avoid fried, processed, and high-sugar foods. There are many ways to eat a balanced diet that’s not too restrictive.

Exercise

Exercise can improve heart health and lower your A1C. It can also reduce the risk of diabetes. But if you don’t regularly exercise, it can be hard to know where to begin. Walking is a great way to start exercising. Research suggests that walking after eating is a good way to lower blood sugar levels. 

If you aren’t already exercising, talk with your healthcare team about how you can safely get moving. 

Lower your cholesterol

If you have a high A1C, you’re also more likely to have high cholesterol. In addition to high blood sugar and a high A1C, high cholesterol is also a risk factor for heart disease. 

To lower your cholesterol, you can start with things like:

• Exercising

• Making dietary changes

• Getting enough sleep

• Quitting smoking (if you do)

But if these changes aren’t enough, there are many medications to help lower cholesterol. Your primary care provider or cardiologist can help you decide which is best for you.

Medications

Medications may be necessary to help reduce A1C, especially if it’s very high or doesn’t improve with diet and exercise. Many different medications lower A1C. Some of the most common ones include:

• Metformin: This medication reduces how much glucose your liver makes and improves how well your body responds to insulin. Metformin can lower your A1C by 1%.

• Sulfonylureas: This group of medications (like glucotrol) causes your pancreas to release more insulin. Insulin causes your cells to absorb glucose so that it’s not too high in the blood. Sulfonylureas also lower A1C by about 1.5%

• Thiazolidinediones: These medications (like pioglitazone) reduce how much glucose your liver makes and improve insulin sensitivity. They improve A1C by 1%.

• Sodium-glucose cotransporter-2 (SGLT2) inhibitors: SGLT2 inhibitors (like Farxiga) cause the kidneys to dump excess glucose into the urine. These medications reduce A1C by just under 1%.

• Dipeptidyl peptidase-4 (DPP-4) inhibitors: DPP-4 inhibitors (like Januvia) prevent the breakdown of a hormone called glucagon-like peptide-1 (GLP-1). GLP-1 helps your pancreas release insulin. It also slows down the liver’s production of glucose. DDP-4 inhibitors help reduce A1C by less than 1%.

Other options to consider include newer GLP-1 receptor agonists. These medications lower A1C by 0.8% to 1.5%. They also decrease the risk of heart disease in people with diabetes.

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Written by:

Frank Schwalbe, MD

Frank Schwalbe, MD, is an assistant professor of anesthesiology at the Yale School of Medicine. He has practiced anesthesiology for 30 years.

Edited by:

Alex Eastman, PhD, RN

Alex Eastman, PhD, RN, is a California-based registered nurse and staff medical editor at GoodRx, where he focuses on clinical updates and Latino health.

Reviewed by:

Sarah A. Samaan, MD

Sarah Samaan, MD, FACC, FACP, FASE is a board-certified cardiologist who practiced clinical cardiology for nearly 30 years. She is a member of the American College of Cardiology and the American College of Physicians, among others.

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