There are two main kinds of diabetes: type 1 diabetes and type 2 diabetes. More than 90% of all people with diabetes have type 2. Overall, more than 3 million Canadians have diabetes, and the number is rapidly rising. Over a third of people with type 2 diabetes are unaware they have the disease and are not receiving the required treatment because, for many people, early symptoms are not noticeable without testing.
Certain genetic markers have been shown to increase the risk of developing Type 1 diabetes. Type 2 diabetes is strongly familial, but it is only recently that some genes have been consistently associated with increased risk for Type 2 diabetes in certain populations. Both types of diabetes are complex diseases caused by mutations in more than one gene, as well as by environmental factors.
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Jump up ^ Kyu HH, Bachman VF, Alexander LT, Mumford JE, Afshin A, Estep K, Veerman JL, Delwiche K, Iannarone ML, Moyer ML, Cercy K, Vos T, Murray CJ, Forouzanfar MH (August 2016). "Physical activity and risk of breast cancer, colon cancer, diabetes, ischemic heart disease, and ischemic stroke events: systematic review and dose-response meta-analysis for the Global Burden of Disease Study 2013". BMJ. 354: i3857. doi:10.1136/bmj.i3857. PMC 4979358. PMID 27510511.
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Insulin is needed to allow glucose to pass from the blood into most of the body cells. Only the cells of the brain and central nervous system can use glucose from the blood in the absence of insulin. Without insulin, most body cells metabolize substances other than glucose for energy. However, fat metabolism in the absence of glucose metabolism, creates ketone bodies which are poisonous and their build up is associated with hyperglycemic coma. In the absence of sufficient insulin, unmetabolized glucose builds up in the blood. Water is drawn from body cells by osmosis to dilute the highly concentrated blood, and is then excreted along with much of the glucose, once the renal threshold for glucose (usually 10 mmol/L) is exceeded. Dehydration follows.

Although some people with this type of diabetes are thin, the majority of people (90%) are overweight. Losing weight, even 2 kg to 5 kg (5 lbs to 10 lbs) can help lower blood glucose levels. For many people, following a healthy diet and an exercise program may be all that is needed to help control glucose levels. For others, healthy eating and exercise alone aren't enough to lower blood glucose levels.
Hyperglycemia (ie, random blood glucose concentration of more than 200 mg/dL or 11 mmol/L) results when insulin deficiency leads to uninhibited gluconeogenesis and prevents the use and storage of circulating glucose. The kidneys cannot reabsorb the excess glucose load, causing glycosuria, osmotic diuresis, thirst, and dehydration. Increased fat and protein breakdown leads to ketone production and weight loss. Without insulin, a child with type 1 diabetes mellitus wastes away and eventually dies due to DKA. The effects of insulin deficiency are shown in the image below.
FIGURE 19-1 ■. This figure shows the hyperbolic relationship of insulin resistance and beta cell function. On the y-axis is beta cell function as reflected in the first-phase insulin response during intravenous (IV) glucose infusion; on the x-axis is insulin sensitivity and its mirror image resistance. In a subject with normal glucose tolerance (NGT) and beta-cell reserve, an increase in insulin resistance results in increased insulin release and normal glucose tolerance. In an individual for whom the capacity to increase insulin release is compromised, increasing insulin resistance with partial or no beta-cell compensation results in progression from normal glucose tolerance, to impaired glucose tolerance (IGT), and finally to diabetes (T2D). Differences between these categories are small at high insulin sensitivity, which may be maintained by weight reduction, exercise, and certain drugs. At a critical degree of insulin resistance, due to obesity or other listed factors, only a further small increment in resistance requires a large increase in insulin output. Those that can increase insulin secretion to this extent retain normal glucose tolerance; those who cannot achieve this degree of insulin secretion (e.g., due to a mild defect in genes regulating insulin synthesis, insulin secretion, insulin action, or an ongoing immune destruction of beta cells) now unmask varying degrees of carbohydrate intolerance. The product of insulin sensitivity (the reciprocal of insulin resistance) and acute insulin response (a measurement beta-cell function) has been called the “disposition index.” This index remains constant in an individual with normal beta cell compensation in response to changes in insulin resistance. IGT, impaired glucose tolerance; NGT, normal glucose tolerance; T2D, type 2 diabetes.
Blurred vision can result from elevated blood sugar. Similarly, fluid that is pulled from the cells into the bloodstream to dilute the sugar can also be pulled from the lenses of your eyes. When the lens of the eye becomes dry, the eye is unable to focus, resulting in blurry vision. It's important that all people diagnosed with type 2 diabetes have a dilated eye exam shortly after diagnosis. Damage to the eye can even occur before a diagnosis of diabetes exists.
Although age of onset and length of the disease process are related to the frequency with which vascular, renal, and neurologic complications develop, there are some patients who remain relatively free of sequelae even into the later years of their lives. Because diabetes mellitus is not a single disease but rather a complex constellation of syndromes, each patient has a unique response to the disease process.
People with full-blown type 2 diabetes are not able to use the hormone insulin properly, and have what’s called insulin resistance. Insulin is necessary for glucose, or sugar, to get from your blood into your cells to be used for energy. When there is not enough insulin — or when the hormone doesn’t function as it should — glucose accumulates in the blood instead of being used by the cells. This sugar accumulation may lead to the aforementioned complications.