Introduction to diabetes mellitus
Diabetes mellitus is a heterogeneous group of diseases characterized by chronic elevation of glucose in the blood. It arises because the body is unable to produce enough insulin for its own needs, either because of impaired insulin secretion, impaired insulin action, or both. Diabetes affects some 300 million people world-wide, and is on the increase. Chronic exposure to high blood glucose is a leading cause of renal failure, visual loss and a range of other types of tissue damage. Diabetes also predisposes to arterial disease, not least because it is often accompanied by hypertension, lipid disorders and obesity. Many cases of diabetes and almost all of its unwanted long-term consequences are potentially avoidable, but this will require intervention at a societal as well as at a medical level. This section of Diapedia offers an introduction to the history of diabetes, its clinical presentation, its current classification and its global epidemiology. We also introduce some of the psychological and societal aspects of diabetes, including the 'hot topics' that dominate the media, and offer an overview of current areas of research interest. All these topics are considered in greater detail elsewhere in Diapedia, and we hope you will explore them further.
History of diabetes
Diabetes was considered a disease of the wealthy in ancient India, and was known as Madhumeha (sweet urine disease); it was observed that ants were attracted to the urine. The ancient Greeks coined the term "diabetes", meaning excessive urination with dehydration, but neither they nor the Romans appreciated that the urine contained sugar; "diabetes" was considered a kidney disease until the 18th century.
The sweet taste of the urine was known to Avicenna (~1000 AD) and to Thomas Willis in the 17th century. The sweet taste was known to be due to glucose by the start of the 19th century, and raised glucose in the blood was recognised soon afterwards. The modern era was heralded by the discovery of Oskar Minkowski that removal of the pancreas resulted in diabetes, followed by the discovery of insulin in 1921-22.
The herbalists of the Middle Ages already knew the beneficial effects of the herb Galega officinalis, which ultimately led to the discovery of metformin. Likewise, Claude Bernard with his 'piqûre diabetique' already suspected that the brain was somehow involved in the causation of diabetes, a topic that continues to attract research attention today. These examples show that many people have made the same observations and considered the same hypotheses at widely differing times, and that valuable findings are sometimes obscured by the fogs of time.
The 'Piskijker' by Jan Steen, showing the role of urine in diagnosing diseases such as diabetes The three classic symptoms of diabetes are thirst, polyuria (excessive urination) and weight loss. As glucose is lost in the urine it draws fluid and other small molecules with it, causing excessive urination, which in turn causes dehydration and thirst. Weight is lost because of rapid breakdown of fat and protein reserves to compensate for the loss of glucose and metabolic inefficiency due to lack of insulin action. These symptoms may be less prominent in older people with type 2 diabetes, who may present with symptoms less directly related to diabetes, or with complications of diabetes ranging from infections to heart disease, or simply as the result of a screening blood test. In this section we describe the elements in the patient's history and physical examination that need attention, and how certain abnormalities are best assessed.
Definition and classification
When thinking about a disease, it helps to have a clear picture of what it is, and what it isn't. And for a disease that affects hundreds of millions of people worldwide, one would expect the definition and classification of diabetes to be fairly straightforward. This, however, is not the case. The definition of diabetes is updated every decade or so, and for the classification we should still heed the words of Elliot Joslin in 1946: 'No method for the classification of diabetics to my mind is satisfactory. ... No sooner are the boundary lines drawn than one case after another like sheep breaks through the fence.' This of course reflects the variation in pathogenetic mechanisms underlying the clinical picture of diabetes.
There are in fact many possible causes of diabetes, and many factors (both genetic and environmental) which influence development of its two main forms, known as type 1 and type 2 diabetes. This section will provide a brief overview of the ways in which diabetes has been defined and classified.
Diabetes world-wideDiabetes is a global disease. Rising on the waves of increasing obesity and increasing age in developing countries, type 2 diabetes mellitus is currently estimated to affect 285 million people, rising to 435 million in 20 years; 6.6% of people aged 20–79 years are believed to be affected.Although quantitatively less important, type 1 diabetes is also on the increase in many populations, and has doubled its incidence in Europe over the past 20–25 years.
In turn, the rise in diabetes is expected to influence cardiovascular morbidity and mortality. Epidemiology is a tool that can be used to detect these changes and to form hypotheses about which factors may be causative or may need to be addressed to prevent or lessen the impact of diabetes. Therefore, the data in this section form an important background when thinking about research and health policy.
Not surprisingly, the diagnosis of diabetes has a profound effect upon many people. For younger people it may represent the first experience of disease, and the realization that the condition is life-long and incurable always comes as a shock. Grief, anger, denial are common reactions, and people may torment themselves by seeking for unlikely explanations or miracle cures. No-one likes diabetes, but a healthy and realistic adjustment is the first step towards taking control of the disorder and getting on with the important things in life.
The societal strains and the intrinsic chronic burden of the disease make diabetes a disease with serious psychological side effects. There is a strong association between diabetes, reduced quality of life and depression. Supporting patients throughout the course of their disease and empowering them to take control of their lives is a major challenge to care-givers.
A chronic disease such as diabetes can sometimes impact upon social life, even in simple matters such as driving, insurance and choice of occupation. These restrictions are sometimes difficult to avoid, but many sporting stars and other role models have shown that diabetes is no barrier to achievement at the highest level.
Just as society can affect those with diabetes, so does diabetes affect societies. Type 2 diabetes in particular is a disorder profoundly influenced by the lifestyle enjoyed by many members of modern societies, so much so that it has reached epidemic proportions. This, and the fact that it is so closely linked to the way we live, have been acknowledged by the United Nations' resolution on World Diabetes Day (14 November) in 2006, and the adoption of the Blue Circle as the international symbol for the fight against diabetes. It is a testimony to the fact that eventually policy-makers in urbanised areas will have to create an environment that prevents diabetes by promoting healthy food choices and exercise, as the only solution to the diabetes epidemic.
Investigating diabetes mellitus
Despite all knowledge already gained about diabetes, we are still a long way off from preventing, properly treating or fully understanding diabetes. Many researchers across the globe try to elucidate the various aspects of the disease. Since much of the content of Diapedia is based on their findings, this section provides an overview of the scientific methods used in diabetes research.
Promising research results, eagerly awaited techniques or unexpected side effects of drugs: whenever there is a new development, there will also be controversy and discussion. Our Hot Topics section, where we try to give you a balanced view of the news, puts these in perspective.