High glucose (blood sugar) can lead to diabetes, heart disease and stroke

Published: June 18, 2018 | Updated: June 18, 2024

Blood glucose, also known as blood sugar, plays a major role in measuring your health. You probably know it’s important, but do you know how your blood sugar number plays a part in conditions such as diabetes, heart disease and stroke? When you have your blood sugar checked, do you know what the number actually means?

What is glucose?

Glucose is a type of energy source for all cells and organs in the body. It comes from the foods that we eat. Carbohydrates (the sugars, starches and fibers found in fruits, grains and vegetables) are one of the main sources of glucose. When broken down, they become sugar in the stomach and are absorbed into the bloodstream. As this travels through your bloodstream to your cells, it’s called blood glucose or blood sugar.

Your body naturally tries to keep the level of glucose in your blood steady. Cells in your pancreas watch your blood sugar level every few seconds. When your blood sugar level rises after you eat, the cells release insulin into your bloodstream. Insulin is a hormone that moves sugar from your blood into cells to be used for energy and storage. People with Type 2 diabetes have higher-than-normal insulin levels in the blood.

How can you find out your blood sugar number?

Two different tests can find your blood glucose or blood sugar number, including a fasting blood sugar test and a glycated hemoglobin (A1C) test.

Fasting blood glucose test

A blood sample is taken after you fast for at least eight hours or overnight.

In general:

• Normal: 70 to 99 milligrams per deciliter (mg/dL)
• Prediabetes: 100 to 125 mg/dL
• Diabetes: 126 mg/dL or higher

Glycated hemoglobin (A1C) test

This test can show your average blood sugar level for the past two to three months. It measures the percentage of glucose attached to the oxygen-carrying protein in red blood cells (hemoglobin). The higher the level, the more sugar attached to your hemoglobin.

In general:

• Normal: Below 5.7 percent
• Prediabetes: 5.7 and 6.4 percent
• Diabetes: 6.5 percent or higher on two different tests

Pregnancy or having a hemoglobin variant, an uncommon form of hemoglobin, can cause an A1C test to be wrong.

Why does your glucose number matter?

Type 2 diabetes causes glucose levels to stay high because the body works harder and harder to make insulin, which can hurt the pancreas over time. When your glucose is high for a long time, it starts to make changes to your body. Your blood vessels can become very weak, causing vascular conditions that can lead to heart disease, heart attack and stroke. It also can make you more at risk for:

• Kidney disease
• Nerve damage in the legs and feet
• Retinopathy, an eye disease that can lead to blindness