ABSTRACT
Diabetes mellitus is a disease characterized by chronic hyperglycaemia (high blood glucose concentration), as well as elevated non-esterified fatty acid (NEFA) concentrations. Over time high blood glucose and NEFA concentrations may lead to a variety of complications which impair quality of life and reduce life expectancy. On average, people with diabetes mellitus die 5-10 years before people without diabetes mellitus. The main cause of premature mortality with diabetes mellitus is cardiovascular disease (CVD) which accounts for 50% of all diabetes fatalities, and much disability. It is estimated that the lifetime risk of developing diabetes mellitus is 32.8% and 38.5% respectively in US males and females born in the year 2000 (Narayan et al. 2003). There are two main forms of diabetes mellitus (henceforth simply called diabetes): type 1 diabetes and type 2 diabetes. Type 1 diabetes (referred to as insulin-dependent diabetes mellitus (IDDM) in older literature) is caused by an autoimmune destruction of the pancreatic beta cells (in the islets of Langerhans). As a result, the pancreas is
Introduction 96 ❚
Aetiology 98 ❚
Prevalence 101 ❚
Obesity as a risk factor 102 ❚
Mechanisms 113 ❚
Exercise as a therapy 115 ❚
Summary 117 ❚
Study tasks 118 ❚
Further reading 118 ❚
unable to produce insulin and this hormone must be injected regularly to control blood glucose concentrations (insulin cannot be given orally because gastrointestinal enzymes would digest it). Type 1 diabetes usually occurs before adulthood, and for this reason is sometimes referred to as juvenile-onset diabetes. In contrast to type 1 diabetes, the defining feature of type 2 diabetes (referred to as non-insulin-dependent diabetes mellitus (NIDDM) in older literature) is unresponsiveness (insensitivity) to the effects of insulin, commonly referred to as insulin resistance. In addition to insulin resistance, the capacity of the pancreas to secrete insulin is impaired in those with type 2 diabetes, although some secretion is maintained. Type 2 diabetes usually occurs in overweight and obese adults aged 40 and over and is sometimes termed maturity-onset diabetes. However, this term is imprecise since type 2 diabetes can occur in children. Type 2 diabetes is the most common form of diabetes, accounting for 85-95% of all diabetes cases in developed countries (International Diabetes Federation 2007). It is difficult to predict who will get type 2 diabetes. Genes are known to play a role. Studies of monozygotic (identical) and dizygotic (non-identical) twin pairs demonstrate higher concordance rates for type 2 diabetes in monozygotic twins (who share a common set of genes). Moreover, offspring whose parents are diabetic are more likely
to develop glucose intolerance and diabetes than offspring of non-diabetic parents. Although such findings are informative, progress in identifying the genetic variants that predispose individuals to type 2 diabetes has been slow and much remains to be learned in this regard (O’Rahilly et al. 2005). Furthermore, although genes may determine susceptibility to diabetes, the International Diabetes Federation (2007) estimates that up to 80% of type 2 diabetes is preventable by adopting a healthy diet and increasing physical activity.
