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Glucose: blood sugar basics

The Body Basics series explains common health terms and medical tests. The series continues with information about blood sugar levels: where glucose comes from, why you need it, and why having too much glucose in your blood can be unhealthy.

Blood glucose or blood sugar level is a measure of the concentration of glucose in your blood. Glucose is a simple sugar that your body gets by breaking down certain foods that you eat (carbohydrates).

Glucose has a very important job: cells and tissues all over your body get the energy they need to move and function from glucose. It reaches all those cells and tissues through your blood. Those cells and tissues then absorb the glucose, removing it from the bloodstream.

Some of those cells and tissues need another ingredient called insulin – a hormone released by the pancreas – to help them absorb the glucose. Insulin is essential for metabolizing (or processing) glucose.

Carbohydrates such as grains and fruit are broken down into glucose. When we eat these foods, the level of glucose in the blood rises, and the pancreas releases insulin to regulate it. As the glucose is absorbed into tissue with the help of insulin, the level of glucose in the blood decreases.

Why it matters

If the body does not produce enough insulin to help the tissues absorb the glucose, or if the body can’t use insulin effectively, then not enough glucose gets absorbed, and more sugar stays in the blood.

When too much glucose stays in the blood, the result is high blood sugar, which is the main characteristic of diabetes. Although glucose is vital to the body, too much glucose circulating in the blood for long periods of time can lead to serious problems, including damage to kidneys, eyes, blood vessels and nerves. These are some of the main complications associated with diabetes.

How is it tested?

Blood sugar levels can be tested in blood samples, but there are different types of blood sugar tests, including:

  • fasting blood sugar
  • post-prandial (after a meal)
  • oral glucose tolerance test

Fasting blood sugar is measured when you haven’t eaten for eight to 10 hours, so this test is often performed early in the morning. This test shows blood sugar levels when the body is not responding to recent glucose intake.

Post-prandial testing is usually performed two hours after a meal. Glucose levels go up after we eat, but after two hours they should be returning to normal. This test helps to see whether the body is processing the glucose.

A glucose tolerance test is actually two or more tests. First, a fasting blood sugar sample is taken. Then the patient is given a glucose solution to drink. Further blood samples are taken at one or more intervals afterward, to see how well the body is processing (or “tolerating”) the dose of glucose.

Glucose tests are used to diagnose diabetes and pre-diabetes (a condition in which blood sugar is higher than normal, but not high enough to be diagnosed as diabetes). Pre-diabetes is sometimes called “impaired glucose tolerance.”

Diabetes

Diabetes is a chronic condition characterized by an abnormally high level of glucose in the blood. There are two main types of diabetes. In Type 1, the insulin-producing cells in the pancreas are damaged, and insulin is no longer produced. Most often this is the result of the body's own immune system damaging these cells. Because there is no insulin to help tissues absorb glucose from the blood, too much glucose stays in the bloodstream and blood sugar levels rise.

Less than 10 per cent of diabetes cases are Type 1, and it usually develops in childhood or young adulthood.

In Type 2 diabetes, there are two possible mechanisms at work. First, the pancreas produces less insulin in response to glucose. Second, the organs and muscles become less sensitive to the effects of insulin, which means insulin is not as effective in helping those tissues absorb glucose. These conditions mean more glucose stays in the blood, resulting in higher blood sugar.

More than 90 per cent of diabetes cases are Type 2, and incidence has increased sharply in recent decades. While it still affects more men than women, prevalence of Type 2 diabetes has been growing rapidly among younger women.

What you can do

Diabetes now affects more than three million Canadians. The escalation in prevalence in recent years is attributed largely to increasing cases of Type 2 diabetes, which corresponds to an increase in risk factors such as obesity, lack of exercise and unhealthy eating habits.

For people who are overweight or obese, weight loss can help to decrease the risk of developing diabetes, or postpone its onset. Even modest weight loss can help.

Maintaining a healthy weight, enjoying regular physical activity, and eating a healthy well-balanced diet can help lower the risk of developing Type 2 diabetes.


Read more on diabetes:

Planning a healthy pregnancy with diabetes

POWER study: rising rates of diabetes in younger women

 Learn more about diabetes in our diabetes health centre.

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A Question of Health

This month's topic: How can I support someone who has been sexually assaulted?
When a person has been sexually assaulted, disclosing and accessing support can be very difficult. While the needs and choices of every survivor are unique, feeling supported when they do disclose the assault can be extremely helpful to their healing process.

  • A publication of:
  • Women's College Hospital