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What is normal blood sugar?

A man measures his blood sugar using a blood glucose monitor.
(Image credit: MixMedia/Getty Images)

Blood sugar, or glucose, is a form of sugar that serves as the body's main source of energy. We obtain glucose from the food we eat, predominantly carbohydrate-rich foods such as potatoes, rice and bread. The absorption and storage of glucose is regulated constantly by complex processes that take place in our digestive systems. 

What constitutes normal blood glucose varies for an individual depending on a range of factors, including age, any underlying medical conditions, and the medications they take — and depends on when they consumed their last meal.

Normal blood sugar before and after meals

Normal blood sugar levels vary from person to person, but a normal range for fasting blood sugar (the amount of glucose in your blood at least eight hours after a meal) is between 70 and 100 milligrams per deciliter (mg/DL), according to the World Health Organization (WHO).

Most people see the level of glucose rise in their blood after eating. According to the American Diabetes Association (ADA), the normal blood-sugar range two hours after eating is generally less than 140 milligrams per deciliter. However, people without prediabetes or diabetes typically have lower blood sugar than those guidelines suggest; a 2007 study in the Journal of Diabetes Science and Technology that continuously measured people's blood glucose found that most people averaged around 82 mg/DL during the night and around 93 mg/DL during the day, and spiked to a maximum of 132 mg/DL an hour after a meal. 

Variations in blood-sugar levels, both before and after meals, are normal and reflect the way that glucose is absorbed and stored by the body. After eating, stomach enzymes break down carbohydrates in food into smaller parts, releasing glucose, which can be absorbed by the small intestine and eventually passed into the bloodstream. 

For a person with type 1 diabetes, the pancreas's beta cells get killed off and so the body can’t produce insulin. Insulin is the key that locks into a certain receptor on the surfaces of your cells and allows glucose (sugar) to leave the bloodstream and enter your cells. Without insulin the sugars just build up in the blood and can’t get into your cells. (Image credit: ttsz/Getty Images)

Once glucose has reached the blood, the pancreas releases the hormone insulin, which shepherds the glucose from the blood into cells, feeding them an essential fuel. 

Generally, our bodies are designed to keep glucose levels constant in the blood — so after all the energy needed is used, any leftover glucose is stored as a compound called glycogen mainly in the liver and the muscles as a backup source of energy if blood glucose levels fall below optimum levels.

When there isn't enough glucose stored to maintain normal blood-sugar levels, the body can also produce its own glucose from noncarbohydrate sources (such as amino acids and glycerol). This process, known as gluconeogenesis, occurs most often during intense exercise or starvation.

While it may seem complicated (and it is), there's a good reason for our bodies to keep up this never-ending dance with glucose: Too much or too little glucose in the blood can lead to serious health problems. 

Too much glucose over an extended time (hyperglycemia) can result in the destruction of nerves, lowered resistance to infection, and heart and kidney disease. 

On the other hand, not enough glucose in the blood over several minutes to hours (hypoglycemia) can affect brain function, causing fatigue, fainting, irritability and, in some cases, seizures, coma and death. 

Blood sugar targets in people with diabetes

People with diabetes often wear a device called a continuous glucose monitor. Here, a woman is using a mobile device to scan the monitor attached to her arm. (Image credit: martin-dm/Getty Images)

In people with diabetes, blood sugar levels are too high, either because the individual isn't making any insulin (type 1 diabetes), or isn't able to make or use insulin efficiently (type 2 diabetes). As a result, glucose levels then remain elevated in the blood and fuel can't enter cells.

Blood sugar targets for diabetes patients are based on how long the person has had diabetes for, their age, and other underlying medical conditions and lifestyle factors. 

But generally, according to the ADA, for most non-pregnant adults with diabetes the fasting blood sugar target range should be in the range of between 80 and 130 mg/DL. Meanwhile, the ADA suggests the after-meal goal about two hours after eating for the same subset of patients should be less than 180 mg/DL. 

Overall, eating plenty of fruit and vegetables, maintaining a healthy weight, and getting regular physical activity alongside medication can all help stabilize and maintain normal blood sugar levels in people with type 2 diabetes.

For pregnant women who have pre-existing diabetes or develop diabetes during pregnancy, ADA guidelines are generally lower. Fasting glucose targets for this population should be less than 95 mg/DL, while they suggest that the after-meal goal about two hours after eating should be below 120 mg/DL.

What is a normal A1C?

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A person's A1C is a measure of their average blood glucose levels over the previous 2 or 3 months, and it is measured through a blood test. A normal result for someone without diabetes or prediabetes would be below 5.7%; an A1C between 5.7% and 6.4% indicates prediabetes; and if your A1C is above 6.4% you would be diagnosed as having diabetes, according to the CDC.

Specifically, the A1C test is a measure of the percent of your red blood cells that have sugar-coated hemoglobin attached to them. The glucose that enters your bloodstream (from carbohydrates that you eat) gets stuck to hemoglobin molecules on red blood cells. And the more glucose in your bloodstream (higher blood sugar levels), the more of your blood's hemoglobin will be "sugar-coated," and the higher your A1C will be, according to the CDC. As such, for people with diabetes (type 1 or 2), the number can give you and your doctors a sense of how well your sugars are being controlled. 

The ADA recommends that most adults with diabetes should keep their A1C below 7% to reduce the risk of diabetes-related complications; the goal is the generally the same for many children with diabetes Targets for the elderly with diabetes are slightly less stringent — for the otherwise healthy with few coexisting chronic illnesses and intact cognitive function, the ADA recommends less than 7.5%, while those who don't meet these requirements have a more lenient goal of below 8.0% to 8.5%. 

According to the Mayo Clinic, higher A1C numbers are linked to a greater risk for diabetes complications, while lower A1Cs have been correlated with a reduced risk of these complications, such as heart disease, kidney disease and vision problems. 

This article is for informational purposes only, and is not meant to offer medical advice.  

This article was updated on Jan. 19, 2022 by Live Science Contributor Natalie Grover.

Additional resources

  • Learn more about how high blood sugar levels put you on the road to developing diabetes and heart disease in this explainer by Harvard Health
  • Read about the risk of high sugar levels and diabetes in pregnant women in this explainer by the Cleveland Clinic
  • Discover the dangers of low blood sugar, with or without diabetes, in this explainer by the Mayo Clinic.
  • Check out this book by Adam Brown, the creator of the column and nonprofit called diaTribe "Bright Spots & Landmines: The Diabetes Guide I Wish Someone Had Handed Me." In it, you'll find tips and strategies from the author who was diagnosed with T1D in 2001. He argues that if you focus on the problems and mistakes of managing the disease (the landmines), you'll miss out on the bigger opportunities (the bright spots).
  • If your child has been diagnosed with type 1 diabetes, this book can help you navigate certain situations and life changes during an overwhelming time. The book, called "The Type 1 Life: A Road Map for Parents of Children with Newly Diagnosed Type 1 Diabetes," is written and published by Jessica Freeman, who gives advice based on her own experience of having the disease.

Bibliography

"The Big Picture: Checking Your Blood Sugar," American Diabetes Association. https://www.diabetes.org/healthy-living/medication-treatments/blood-glucose-testing-and-control/checking-your-blood-sugar

"Mean fasting blood glucose." World Health Organization. https://www.who.int/data/gho/indicator-metadata-registry/imr-details/2380 

"Continuous Glucose Profiles in Healthy Subjects under Everyday Life Conditions and after Different Meals" 2017, Journal of Diabetes Science and Technology https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769652/ 

"Management of Diabetes in Pregnancy: Standards of Medical Care in Diabetes—2021." ADA. https://diabetesjournals.org/care/article/44/Supplement_1/S200/30761/14-Management-of-Diabetes-in-Pregnancy-Standards  

"Diabetes tests." CDC. https://www.cdc.gov/diabetes/basics/getting-tested.html 

"Understanding A1C." ADA. https://www.diabetes.org/a1c

"Older Adults: Standards of Medical Care in Diabetes—2021." ADA. https://diabetesjournals.org/care/article/44/Supplement_1/S168/30583/12-Older-Adults-Standards-of-Medical-Care-in

"A1C test." Mayo Clinic. https://www.mayoclinic.org/tests-procedures/a1c-test/about/pac-20384643

Originally published on Live Science.

Natalie Grover is a contributing writer for Live Science, covering all things health and science. She spent her formative years as a journalist with Reuters, writing about the business of health. Based in London, UK, she has a masters degree in medicine, health and public policy, and is working on making her coverage statistically significant. In her free time, she monitors her wildly fluctuating heartbeat whilst watching Arsenal FC (and enjoys long walks on the beach). Most days she can be found at the gym and aiming to feed her family healthy food.