What to Know About Blood Glucose Levels

Blood glucose, or blood sugar, is produced from carbohydrates in the diet to supply the cells throughout the body with energy. Normally, the body regulates blood glucose levels so there's always enough to fuel cells but not so much that the bloodstream is overloaded with sugar, which could cause significant damage.

For people with diabetes, the balancing of blood glucose levels is thrown off due to problems with insulin, a hormone produced by the pancreas that helps keep blood glucose levels steady and stable. In type 1 diabetes, the pancreas does not produce insulin at all. In type 2 diabetes, it produces too little insulin and/or the body isn't able to use it properly. The same is true for gestational diabetes, a temporary form of the disease the develops during pregnancy.

Because blood sugar fluctuates throughout the day depending on when food was last eaten, what was eaten, physical exertion, and other factors, monitoring glucose levels is a key aspect of managing all types of diabetes—particularly for those who take insulin.

Ideal Blood Glucose Levels

The specific level of blood glucose that's considered ideal for an individual depends on their age, how long they've had diabetes, medications they take, and any other medical conditions they may have, among other factors.

What's more, various health organizations differ in what they consider to be ideal glucose levels. Ultimately, if you have diabetes and blood glucose monitoring is a part of your treatment strategy, your doctor will have the last word on what your target glucose levels at any given time during the day should be. Even so, there are some general parameters worth knowing about, according to the American Diabetes Association (ADA).

Fasting Blood Glucose

Everyone experiences a hormone surge called the "dawn phenomenon" each morning several hours before they wake up. For people with diabetes, this hormone surge results in higher-than-normal blood sugar levels because they don't have a normal insulin response to adjust for it.

The dawn phenomenon happens because during the night the body produces less insulin while at the same time the liver produces more glucose. The lack of insulin results in a blood sugar rise in the morning.

If your fasting blood glucose is higher or lower than ideal most mornings, it may help to eat dinner earlier and avoid carbohydrates late at night. Exercising in the evening also may help keep your morning blood sugar within range. If you're on a diabetes medication, your doctor may want to adjust the time you take it or switching to a different one also may help.

Preprandial (Pre-meal)

Preprandial blood glucose refers to the level of sugar in the bloodstream before eating. Determining your pre-meal blood glucose and—this is key—recording it in a journal or with an app, will allow you and your doctor to identify trends in how your blood sugar levels rise and fall over time, which is an indication of how well your diabetes treatment is working.

Postprandial (Post-meal)

Postprandial blood glucose refers to blood sugar levels within an hour or two after meals and snacks. As with preprandial blood glucose testing, it's important to record your level each time you take it. You also should write down everything you ate and how much. This provides further information about how your body responds to certain foods, which in turn will help you and your doctor fine-tune your diet and other aspects of your diabetes management plan.

Before and After Exercise

Regular physical activity generally is a key part of managing diabetes, especially for people with type 2 diabetes for whom losing weight could make an enormous difference in overall health. For those with type 1 diabetes, exercise can help increase sensitivity to insulin and control blood sugar.

However, because physical activity uses energy, it depletes cells of glucose, drawing glucose from the bloodstream and potentially leading to hypoglycemia. It's important, then, to check your blood sugar levels before you exercise as well as immediately afterward. This way you'll know if you have enough glucose to fuel your workout and you'll know the degree to which you've depleted it while exercising.

Target glucose ranges vary from person to person, but in general, it's ideal for blood sugar levels to be between 126 mg/dL and 180 mg/dL before starting exercise. If you test your blood glucose and it's lower than 126 mg/dL, here are the steps to take depending on the exact reading you get:

After you work out, test your blood glucose right away and again two to four hours afterward to check for a delayed drop in your level. If your blood sugar is lower at this point, continue checking it every two to four hours or until it's no longer low and you're sure your glycogen has been restored to normal.

A1C Test Levels

Besides having you self-test your glucose levels, your doctor likely will have you in several times a year (more often if you've just been diagnosed) to undergo a hemoglobin A1C test. This is a blood test that reveals average blood glucose levels over the previous two to three months that can help you and your doctor monitor your overall glucose control.

A Word From Verywell

Testing your blood glucose throughout the day will help you to control it by revealing how food, exercise, stress, illness, and other factors affect your levels. Your doctor, certified diabetes educator, or health care provider will help you develop a daily testing routine that works with your schedule. If you take insulin or an oral diabetes medication that can cause hypoglycemia (low blood sugar), or if you have poor glucose control, you probably will need to test your blood sugar fairly often, but this is not a bad thing: It simply means you need to keep close tabs on any fluctuations in your glucose levels so that you deal with them and then go on with your day.