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ОглавлениеChapter 1 Introduction to diabetes
KEY POINTS
Diabetes is common, and its incidence is rising.
Type 2 diabetes is by far the most common accounting for 85–95% of cases.
Complications in the microvasculature (eye, kidney and nerve) and the macrovasculature are responsible for considerable morbidity and excess mortality.
Mortality from some complications is decreasing but absolute numbers for many are still rising.
Diabetes mellitus is a condition of chronically elevated blood glucose concentrations which give rise to its main symptom of passing large quantities of sweet–tasting urine (diabetes from the Greek word meaning ‘a siphon’, as the body acts as a conduit for the excess fluid, and mellitus from the Greek and Latin for honey). The fundamental underlying abnormality is a net (relative or absolute) deficiency of the hormone insulin. Insulin is essentially the only hormone that can lower blood glucose.
There are two main types of diabetes: type 1 is caused by an autoimmune destruction of the insulin‐producing β cell of the islets of Langerhans in the pancreas (absolute deficiency); and type 2 is a result of both impaired insulin secretion and resistance to its action – often secondary to obesity (relative deficiency).
The precise level of blood glucose that defines diabetes has been revised several times and is covered in more detail in Chapter 3. Diabetes is common and is becoming more common. In absolute numbers, globally there are 463 million people aged 20–79 with known diabetes in 2019, projected to rise to 700 million in 2045. Alarmingly it is thought that there are almost as many again with undiagnosed diabetes. World‐wide, age‐adjusted prevalence is set to rise from 9.3 to 10.9% in 2045. The numbers of those with impaired glucose tolerance are equally startling with a prevalence of 7.5% in 2019, projected to rise to 8.6% in 2045 (Figure 1.1). The relative proportions of type 1 to type 2 vary from 15 : 85% for Western populations to 5 : 95% in developing countries.
It is the short‐ and long‐term complications of diabetes which make it a major public health problem. Absolute deficiency of insulin leads to ketoacidosis and coma with an appreciable mortality even in the UK and other Western countries. Hyperglycaemic hyperosmolar state is less common but remains an equally serious problem for people with type 2 diabetes (see Chapter 12).
Long‐term hyperglycaemia affects the microvasculature of the eye, kidney, and nerve as well as the larger arteries, leading to accelerated atherosclerosis. Diabetes is the most common cause of blindness in those of working age, the most common single cause of end‐stage renal failure worldwide, and the consequences of neuropathy and peripheral vascular disease make it the most common cause of non‐traumatic lower limb amputation. Diabetes and its complications are estimated to account for 11.3% of all cause mortality in adults aged 20–79 years in 2019 and nearly 50% of these are in people of working age (< 60 years). Mortality from ischaemic heart disease and stroke is 2–4‐fold higher than in the age‐ and sex‐matched non‐diabetic population (Figure 1.2). These relative rates have not substantially changed since the last edition, although, encouragingly, mortality rates from acute myocardial infarction and hyperglycaemic crises have reduced, at least in the USA and Sweden (Figure 1.3). Because of the increasing numbers of people with diabetes, however, absolute numbers experiencing stroke, amputation, and end stage renal disease are increasing with massive associated financial costs. In 2019 the IDF estimates total diabetes healthcare expenditure will be US$760 billion and predicts that this will rise to US$ 825 billion in 2030 and US$ 845 billion by 2045 (Figure 1.4).
Figure 1.1 Estimated comparative raw prevalence of diabetes and impaired glucose tolerance (IGT) together with numbers affected for the global population age 20–79 years for 2019 (BLUE) and 2045 (RED). Data from Diabetes Atlas, 9th edn, International Diabetes Federation.
Figure 1.2 Rates of major complications of diabetes for the US population derived from NHANES or Medicare data. aNHANES data 1988–2000; bMedicare population Minnesota 1993–5; cNHANES data, 1999–2006 (chronic kidney disease defined as estimated GFR <60 mL/min/1.73 m2.); dNHANES data, 1999–2002.
This handbook sets out to cover the essentials of diagnosis, epidemiology and management of diabetes and its’ distressingly many complications. By using case vignettes and summaries of key trials together with web links and suggestions for further reading, it will hopefully serve as a useful desktop reference for all healthcare professionals who provide diabetes care.
Figure 1.3 Age standardised mortality rates from diabetes‐related complications in the US population with known diabetes 1990–2010. Circle size is proportional to the absolute number of cases. The table shows the rate per 10,000 population with or without diabetes. AMI = acute myocardial infarction, ESRD = End Stage Renal Disease. Figure and data from Gregg, E.W. et al. NEJM 2014; 370:1514–23 with permission
Figure 1.4 Estimated global diabetes-related healthcare costs for adults aged 20–79 years in 2019, 2030 and 2045.
Source: IDF Diabetes Atlas 9th Edition 2019.
FURTHER READING
1 International Diabetes Federation. Diabetes Atlas, 9th edn. Brussels: International Diabetes Federation, 2019.
