(Also known as: Diabetes mellitus)

Normally, when blood glucose levels rise after a meal, the pancreas (an organ near the stomach) releases a hormone called insulin to stimulate your cells and liver to absorb the glucose. With diabetes, the body either does not produce enough insulin (type 1 diabetes) or cannot use the hormone effectively (type 2 diabetes). This causes glucose levels in the blood to rise.

High levels of sugar in the blood can increase the buildup of fatty deposits on blood vessel walls, narrowing the walls and reducing blood flow. Over time, these deposits may harden or clog the vessels, resulting in coronary artery disease.

A shortage of sugar delivered to the body’s cells from the bloodstream also reduces the amount of energy available to them, leading to long-term complications of the small blood vessels in the eyes, kidneys and nerves.

People with diabetes have three to five times the risk of heart disease of people without the condition. This risk is greater for women than men. People with diabetes are also more likely to be overweight due to insulin resistance and have high blood pressure and high cholesterol, all of which are strongly linked to heart and vascular disease.

Types of Diabetes

There are three main types of diabetes:

  • Type 1 Diabetes: In type 1 diabetes, the body stops making insulin. This happens because the body’s immune system mistakenly attacks and destroys part of the pancreas. The condition usually develops in childhood or adolescence, but it can be found in a smaller number of adults and is known as latent autoimmune diabetes in adulthood (LADA). About 5 to 10% of people with diabetes have type 1.
  • Type 2 Diabetes: In type 2 diabetes, either the pancreas produces too little insulin or the body cannot use insulin properly, causing blood sugar levels to rise. Most adults with diabetes have type 2. There has been a rise in type 2 diabetes in adolescents, with unhealthy lifestyle being the trigger.
  • Gestational Diabetes: Gestational diabetes is a temporary condition that can occur during pregnancy, due to hormone changes. Women who develop gestational diabetes have an increased risk of developing type 2 diabetes later in life.

Prediabetes is a related condition in which blood sugar levels are higher than normal, but not high enough to be considered diabetes. Having prediabetes increases a person’s risk for cardiovascular disease. Nearly half of people with prediabetes will develop type 2 diabetes later in their lives.

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Type 1 diabetes, primarily found in genetically predisposed individuals, is caused by a combination of genetic factors and environmental exposures that trigger the immune system to attack the pancreas. It cannot be prevented.

Some factors that contribute to the risk of developing type 2 or gestational diabetes—such as age, genetic factors or ethnicity—cannot be changed. But others—such as abdominal obesity, high cholesterol and high blood pressure—can be treated to reduce the risk.

Risk factors for type 2 diabetes include:

  • Age (being 40 years or older)
  • Family history (having first-degree relatives with diabetes)
  • Ethnicity (being of aboriginal, Hispanic, Asian, South Asian or African descent)
  • Being obese or having an elevated waist circumference
  • Having a diagnosis of prediabetes or gestational diabetes, high blood pressure, high cholesterol, obstructive sleep apnea or schizophrenia
  • Giving birth to a baby weighing more than 4 kg (9 lbs)
  • Having a diagnosis of polycystic ovary syndrome or acanthosis nigricans (a skin disorder)
  • Taking corticosteroids


A test called the hemoglobin A1c (HbA1c) is used at the Ottawa Heart Institute to diagnose diabetes. This test provides an average of blood glucose levels over the previous two to three months. The A1c test provides a fuller picture of how well a person metabolizes sugar than the more commonly used fasting glucose test, which gives only a snapshot of blood glucose at a moment in time. A1c can be measured at any time of day and is a continuous cardiovascular risk factor, making it a better predictor of large vessel disease than the fasting blood glucose.

People over the age of 40 should be tested for diabetes every three years. People with one or more risk factors for diabetes should be tested more frequently.


Many people who have diabetes have no symptoms. Often, type 2 diabetes is only diagnosed in the process of treating a heart condition. When a person with diabetes does have symptoms, they can include:

  • Increased thirst
  • Frequent urination
  • Weight gain/loss
  • Extreme fatigue/loss of energy
  • Blurred vision
  • Frequent or recurring infections
  • Cuts or bruises that are slow to heal
  • Tingling or numbness in the hands or feet
  • Trouble getting or maintaining an erection


Type 1 diabetes is treated solely with insulin either by multiple injections or via subcutaneous insulin pumps.

Type 2 diabetes can often be managed initially or even reversed with lifestyle changes. These include:

  • Physical Activity: People with diabetes should get a minimum of 150 minutes of moderate to vigorous activity each week, spread over at least three days, with no more than two consecutive days without exercise.
  • Diet: People with diabetes should limit eating refined carbohydrates, including sweets and foods with a high glycemic index, such as breads, pastas, potatoes and rice. Choosing foods in smaller portions from all food groups at each of the three meals, spaced 4 to 6 hours apart, will aid in stabilizing glucose control.
    • Workshops on “Eating Well with Diabetes” are available through the Ottawa Heart Institute’s Prevention and Wellness Centre (call 613-696-7071 to register).
  • Weight Management: Losing even 5% of your body weight can help your body use insulin more efficiently.

People with diabetes who are on medications or taking insulin will need to monitor their own blood sugar regularly. Monitors are available that let you test your own blood sugar at home. If you have diabetes, you should aim for a target of 4 to 7 mmol/l immediately before eating. Work with your health care provider to determine your personal upper and lower limits for blood sugar after meals in order to achieve an A1c of 7% or less.

If lifestyle changes alone cannot bring blood sugar down to target levels, oral medications and insulin will be necessary to achieve control and avoid long-term complications. These can include a number of medications targeting different areas of the body that control blood glucose levels. Diabetes Canada has more information on blood glucose-lowering therapies.

  • Metformin: This safe and effective drug remains the first agent to use at diagnosis of type 2 diabetes with lifestyle intervention. This drug helps your body use the insulin it produces more effectively.

Gestational diabetes may also require treatment with medication for the course of a woman’s pregnancy.

For more information, see our Diabetes Education Videos.