Diabetes mellitus is a chronic condition that arises when the pancreas does not produce enough insulin, or when the body cannot effectively use the insulin produced. Failure of insulin secretion, insulin action or both leads to raised glucose levels in the blood (hyperglycaemia) which, if uncontrolled, can cause serious complications. The most important of these are retinopathyRetinopathy is a disease of the retina of the eye which may cause visual impairment and blindness. (affecting the eyes), nephropathyDisease caused by damage to the small vessels of the kidneys. It results in loss of protein in the urine, high blood pressure and progressive kidney failure. (affecting the kidneys), neuropathyDamage to the nerve fibres caused by diabetes. Long nerves are most affected and so the process is usually first noticed in the feet with a numbness and loss of sensation. (affecting the nerves) and cardiovascular diseaseCardiovascular diseases are defined as diseases and injuries of the circulatory system: the heart, the blood vessels of the heart, and the system of blood vessels throughout the body and to (and in) the brain. Stroke is the result of a blood flow problem within, or leading to, the brain and is considered a form of cardiovascular disease. (affecting the circulatory system).
While diabetes is always diagnosed using standard diagnostic criteria, it is a heterogenous disorder with several different types described, each with a different cause. The two major types recognized are type 1 diabetes and type 2 diabetes. Previously known as insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM) respectively, the terms type 1 and type 2 are used to avoid individuals being classified based on their treatment, rather than the cause of their disease.
| The four main types of diabetes | ||
|---|---|---|
| 1 | Type 1 diabetes | Insulin required for survival due to a lack of insulin produced by the body as a result of beta cell destruction. |
| 2 | Type 2 diabetes | Characterised by disorders of both insulin action or secretion, either of which may predominate, but both of which are usually present. Usually controlled by diet, exercise and oral hypoglycaemic agents. Insulin may be required for metabolic control. |
| 3 | Other specific types of diabetes | Other types of diabetes where the cause is known (e.g. genetic defects in beta cell function or insulin action, diseases of the pancreas, certain other hormonal disorders, or drug induced disorders). |
| 4 | Gestational diabetes | Diabetes appearing for the first time in pregnancy. |
Lesser degrees of abnormal glucose levels are also recognized. These include impaired glucose tolerance (IGT)Blood glucose levels that are higher than normal but below the level of a person with diabetes., blood levels that are higher than normal but below the level of someone with diabetes, and impaired fasting glycaemia (IFG)Raised fasting levels of glucose., raised fasting levels of glucose. Compared with individuals with normal blood glucose levels, those with IGT or IFG have an increased risk of progressing to diabetes.
Type 2 diabetes, which accounts for over 90% of diabetes cases globally, was previously thought of as a distinct disease entity, but many cases are now considered to be a manifestation of a much broader underlying disorder known as the metabolic syndrome. This refers to a clustering of type 2 diabetes or IGT with several other major disease risk factors such as for diabetes (impaired glucose tolerance, central obesity, abnormal levels of lipids (dyslipidaemia), high blood pressure and insulin resistance). Debate still continues as to the primary aetiological factor underlying the metabolic syndrome.
| Components of the metabolic syndrome |
|---|
| Central obesity |
| Dyslipidaemia |
| Hypertension |
| Impaired glucose regulation or diabetes |
| Insulin resistance |
| Microalbuminuria |