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What Are Normal Blood Sugar Levels?

Updated on May 28, 2017

Sugar goes by many names and comes in many shapes and forms in the food we eat. Blood sugar is a term used to refer to blood glucose. It is a measure of how much glucose is present in the blood. Glucose is the main source of fuel for energy production in our cells. The human brain runs almost exclusively on glucose. However, abnormally high or abnormally low blood glucose levels can be life-threatening.

Blood sugar fluctuates throughout the day depending on food intake, exercise and other factors. Our body has mechanisms in place that maintain a healthy supply of glucose throughout the body. This involves the release of glucose if blood sugar falls below a threshold or the removal of glucose if the blood sugar rises above a threshold. A malfunction in one or more of these mechanisms will lead to a metabolic disorder such as diabetes. Keeping track of your blood sugar is an important step towards understanding the cause of abnormal fluctuations in your blood sugar levels.

Self-monitoring of blood glucose can be done by using a glucose meter. The standard unit for measuring blood glucose in the United States and Europe is milligrams per decilitre (mg/dL). In the UK and Canada, the most common unit for measuring blood glucose is millimol per litre (mmol/L).

Normal Blood Sugar Levels for Adults Without Diabetes

A preprandial blood sugar measurement is one taken before meal. It is usually measured after fasting for at least 8 hours, hence also referred to as fasting blood sugar. The normal fasting blood sugar in a healthy adult without diabetes is around 80 mg/dL (that is 4.4 mmol/L). This is less than one teaspoonful of sugar in the whole blood volume of an average person.

According to the American Diabetes Association (ADA), a normal fasting blood sugar for a non-pregnant adult is between 70 and 100 mg/dL (which is 3.9 and 5.6 mmol/L). After a normal meal (postprandial), blood sugar gradually goes up. A normal blood glucose level measured 1 to 2 hours after the start of a meal is less than 140 mg/dL (< 7.8 mmol/L) for someone without diabetes.

Normal Range
Fasting Blood Sugar
70 – 100 mg/dL (3.9 to 5.6 mmol/L)
2 hours After Meal
under 140 mg/dL (under 7.8 mmol/L)
Normal blood sugar range for people without diabetes. Source: American Diabetes Association

Target Blood Sugar Levels for Adults With Diabetes

For people with diabetes, the target fasting blood sugar range set by ADA is from 80 to130 mg/dL (that is 4.5 to 7.3 mmol/L). And the target range for a postprandial blood sugar (2 hours after meal) is less than 180 mg/dL (< 10.0 mmol/L).

Target Range
Fasting Blood Sugar
80 – 130 mg/dL (4.5 to 7.3 mmol/L)
2 hours After Meal
under 180 mg/dL (under 10.0 mmol/L)
Target blood sugar range for people with diabetes. Source: American Diabetes Association

Glucose Meter

What Happens to the Sugar You Eat?

Minutes after consuming a meal, the digestive system begins breaking down carbohydrates into smaller usable molecules like glucose. Glucose molecules are then absorbed into the blood stream causing a temporal spike in blood sugar, without reaching 140 mg/dL (7.8 mmol/L). Glucose-rich blood travels throughout the body and stimulates the pancreas to secrete insulin, a peptide hormone that triggers the uptake of glucose into cells where they are metabolized to generate ATP – the main fuel for all body cells. Insulin also stimulates liver cells to convert glucose into glycogen which is the storage form for glucose in the liver. The insulin response drives down blood sugar to normal levels. Blood sugar usually drops below 100 mg/dL (5.6 mmol/L) at 2 hours after the start of the meal. Beyond 2 hours, it returns to fasting blood sugar range until the next meal.

Profile of normal blood sugar levels throughout the day
Profile of normal blood sugar levels throughout the day | Source

During fasting or prolonged exercise when blood sugar falls below normal, the pancreas jumps in to bring the blood glucose back up to normal. The pancreas secretes a hormone called glucagon which has an opposite effect to that of insulin. Glucagon promotes the conversion of glycogen stored in the liver back to glucose driving blood glucose back up to normal.

Glucose homeostasis is the tendency for the body to maintain stable blood sugar levels through careful regulation by hormone signals. That is, if blood sugar levels stray out of normal limits, the amount of insulin and glucagon secretions are adjusted accordingly.

Diabetes and Hypoglycemia

Type I diabetes is when a person loses the ability to produce insulin. In Type II diabetes, a person has insufficient insulin to trigger the uptake of glucose into cells. There are people with type II diabetes who have sufficient insulin but the problem is that their cells are resistant to it.

If your blood sugar measurements are persistently above the upper limits of normal, this may suggest that your body is not regulating blood sugar properly, this can be due to diabetes. On the other hand, when your blood sugar gets below 70 mg/dL, you develop low blood sugar referred to as hypoglycemia.

Hypoglycemia is a life-threatening condition that occurs when the amount of glucose in the blood drops to a dangerously low level. Hypoglycemia episodes are common in diabetics who use insulin or other glucose lowering medications. An attack can be caused by a very high level of insulin in the blood.

More on Diabetes


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Statistics from the ADA show that over 9% of Americans had diabetes in 2012. This is more than 29 million people. During the same period 86 million Americans younger than 20 years were found to have prediabetes. The number of diabetics and prediabetics seems to be on a steady increase each year.

Final Comment

Normal ranges for blood sugar is individualized. A more or a less strict normal range may be appropriate depending on a person's demographics, health and other factors. A normal blood sugar level is not necessarily a healthy blood sugar level for certain individuals. Even though the term ‘normal blood sugar levels’ is used, a result at the upper or lower bound of the normal range may still be an indicator of a health issue. Hence, be sure to talk to your health care provider about your blood sugar.


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