Characteristic symptoms of diabetes are polyuria, thirst, blurring of vision and weight loss. Other non-specific symptoms, such as weakness, tiredness and depressive symptoms are also common. If left untreated severe vascular and other complications occur.

The commonest form – constituting 80-85% of cases – is now named Type 2 diabetes. It was earlier called non-insulin dependent diabetes (NIDDM) and was primarily associated with diabetes affecting elderly, but this form becomes increasingly common among younger age groups. Type 2 diabetes is primarily caused by impaired response to insulin – insulin resistance – in which the body’s response to insulin is ineffective. As to the process that causes Type 2 diabetes, there are few sensitive or specific indicators.

Type 1 diabetes, formerly often called child or adolescent diabetes is the second commonest form. Even though this form is mainly found in young persons, it may also affect adults. Type 1 diabetes is an autoimmune disease, in which autoantibodies destroy the insulin-producing cells in the pancreas. It was formerly named insulin-dependent diabetes (IDDM), as these patients have to be substituted with insulin. Type 1 diabetes includes the majority of cases primarily caused by pancreatic islet cell antibodies, both those attributable to an autoimmune process, and those with beta-cell destruction without any specific cause. Latent Autoimmune Diabetes in Adults (LADA) is a milder form of Type 1 diabetes that affects elderly, and that constitutes about 10% of type I diabetes.

Pregnancy-related diabetes and a rare form called Maturity Onset Diabetes (MODY) are other variants of diabetes. There are also several other forms that may be associated with for instance infections, a range of endocrine and other disorders, or with exposure to certain drugs.

Independent of the type of diabetes the severity can be categorised by stages of impaired glucose regulation and clinical characteristics. Regardless of aetiology, individuals may move from stage to stage in both directions, although the disease is a chronic condition.

The incidence of diabetes varies greatly from country to country. Type 1 diabetes is commonest in northern Europe, whereas it is rare in East Asia, for instance. Some of the differences may be explained by genetic variations, but changes in lifestyle must have an impact, as the incidence has more than doubled during the last five decades. Epigenetic factors may contribute; that is conditions during gestation may alter the genetic expression and predispose for the disease if environmental conditions, such as food intake, changes later in life.

The incidence of Type 2 diabetes increases worldwide and in particular rapidly in several developing countries, where lifestyle rapidly changes towards a western pattern.

As prevalence depends on both incidence and survival, it is influenced by demographic changes as well. In many developing countries, the prevalence starts to rise at earlier ages and total prevalence may exceed rates found in the industrialised world. The worldwide prevalence of diabetes was estimated to be over 150 millions in the year 2000, and likely to exceed 200 millions in 2010. Only about 50% of diabetics are, however, diagnosed. Of these about 20% is insulin dependent.

Impaired glucose regulation

Normally fasting blood/plasma glucose levels lie between 3.5 and 4.5 mmol/L. After a meal levels increase more or less depending of the kind of food ingested. Postprandial levels can reach 8mmol/L.

Impaired glucose regulation refers to a metabolic state between normal glucose regulation and diabetes. It is defined as Impaired Fasting Glycaemia (IFG) and/or Impaired Glucose Tolerance (IGT), which reflect different abnormalities of glucose regulation. IFG reflects the fasting, and IGT the postprandial state. Abnormal IGT is a stage in the development of disordered carbohydrate metabolism. IFG refers to fasting glucose levels that are lower than those required for the diagnosis of diabetes, but higher than the “normal” reference range. The new definition of impaired fasting glucose (IFG) of 100-125 mg/dL (5.6-6.9 mmol/L) in non-diabetics, was used to identify IFG in 8,814 participants, 20 years or older, in the Third National Health and Nutrition Examination Survey. The prevalence of IFG then increased from 5.5% under the old definition to 20.4% under the new one. Both IGT and IFG are associated with increased risk of developing diabetes and cardiovascular disease.

The metabolic syndrome – Syndrome X

The metabolic syndrome, also named Syndrome X, is a condition currently very much in focus. It is associated with overweight or obesity, hypertension and disturbed blood lipid pattern. The syndrome is also often accompanied by impaired glucose regulation. For long periods the body may, however, compensate for insulin resistance by increasing the insulin production, and therefore it may take many years before the glycemic disorder is diagnosed. About one third of severely obese subjects sooner or later become diabetic. Insulin resistance is exacerbated by smoking, and a large proportion of these patients smoke.

The metabolic syndrome is very common in the western world. The prevalence was previously estimated to be about 10% of the western populations, but newer criteria have considerably increased this estimation. The prevalence increased from 21.8 to 26.3% when the new definition of impaired fasting glucose (IFG) of 100-125 mg/dL (5.6-6.9mmol/L) was used in non-diabetics, to identify IFG as well as the metabolic syndrome in 8,814 participants, 20 years or older, from the Third National Health and Nutrition Examination Survey. Using the National Cholesterol Education Program Expert Panel - Adult Treatment Panel definitions (NCEP-ATP111), the prevalence in the US of the metabolic syndrome was recently reported to be 31% in men and 35% in women 35 years or older.

The incidence of the metabolic syndrome is increasing very rapidly in developing countries, where life style changes towards a western urbanized pattern. The lowest prevalence is found in Taiwan with 11% of the men and 12% of the women meeting the criteria. Women are thus somewhat more likely to develop the syndrome than men. The risk factors that defined the metabolic syndrome, however, did vary between countries so that the groups from different regions were heterogeneous. In many developing countries the disease develops earlier and the prevalence of diabetes may exceed the prevalence in the industrialized world. The evolution is particularly dramatic in China, India, Sri Lanka, the Middle East and Latin America.

The metabolic syndrome constitutes an important risk factor for the development of not only diabetes, but is also an important precursor to cardiovascular disease, and is a risk factor for several other diseases. The metabolic syndrome is over represented among patients with cardiovascular and other disorders. In an unselected population of 633 patients with acute myocardial infarction, it was for instance recently found that 46% fulfilled the criteria for the metabolic syndrome. Those patients also had a worse outcome with increased risk of severe heart failure, and hyperglycaemia was the main correlate of the risk of development of severe heart failure. A high prevalence (38-53%) of the metabolic syndrome that varied with sex and definition was also found in a survey of 1,424 Japanese patients. In female patients, only the WHO criteria of the metabolic syndrome were predictive for cardiovascular disease during an 8-year follow-up.