Diabetes mellitus is a diagnostic term for a group of disorders characterized by abnormal glucose homeostasis resulting in elevated blood sugar. There is variability in its manifestations, wherein some individuals have only asymptomatic glucose intolerance, while others present acutely with diabetic ketoacidosis, and still others develop chronic complications such as nephropathy, neuropathy, retinopathy, or accelerated atherosclerosis. It is among the most common of chronic disorders, affecting up to 5–10% of the adult population of the Western world. Its prevalence varies over the globe, with certain populations, including some American Indian tribes and the inhabitants of Micronesia and Polynesia, having extremely high rates of diabetes (1,2). The prevalence of diabetes is increasing dramatically and it has been estimated that the worldwide prevalence will increase by more than 50% between the years 2000 and 2030 (3).
Glucose is a simple sugar found in food. Glucose is an essential nutrient that provides energy for the proper functioning of the body cells. Carbohydrates are broken down in the small intestine and the glucose in digested food is then absorbed by the intestinal cells into the bloodstream, and is carried by the bloodstream to all the cells in the body where it is utilized. However, glucose cannot enter the cells alone and needs insulin to aid in its transport into the cells. Without insulin, the cells become starved of glucose energy despite the presence of abundant glucose in the bloodstream. In certain types of diabetes, the cells' inability to utilize glucose gives rise to the ironic situation of "starvation in the midst of plenty". The abundant, unutilized glucose is wastefully excreted in the urine.
Diabetes mellitus type 2 is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency.[51] This is in contrast to diabetes mellitus type 1 in which there is an absolute insulin deficiency due to destruction of islet cells in the pancreas and gestational diabetes mellitus that is a new onset of high blood sugars associated with pregnancy.[13] Type 1 and type 2 diabetes can typically be distinguished based on the presenting circumstances.[48] If the diagnosis is in doubt antibody testing may be useful to confirm type 1 diabetes and C-peptide levels may be useful to confirm type 2 diabetes,[52] with C-peptide levels normal or high in type 2 diabetes, but low in type 1 diabetes.[53]
Dr. May currently works as a fulltime endocrinologist and has been in private practice since 2004. He has a variety of interests, predominantly obesity and diabetes, but also sees patients with osteoporosis, thyroid disorders, men's health disorders, pituitary and adrenal disorders, polycystic ovaries, and disorders of growth. He is a leading member of several obesity and diabetes societies and runs a trial centre for new drugs.
Diabetes is a disease in which your blood glucose, or blood sugar, levels are too high. Glucose comes from the foods you eat. Insulin is a hormone that helps the glucose get into your cells to give them energy. With type 1 diabetes, your body does not make insulin. With type 2 diabetes, the more common type, your body does not make or use insulin well. Without enough insulin, the glucose stays in your blood.
In animals, diabetes is most commonly encountered in dogs and cats. Middle-aged animals are most commonly affected. Female dogs are twice as likely to be affected as males, while according to some sources, male cats are also more prone than females. In both species, all breeds may be affected, but some small dog breeds are particularly likely to develop diabetes, such as Miniature Poodles.[123]
Screening for undiagnosed T2DM is recommended at the first prenatal visit in women with above risk factors, using standard diagnostic method criteria. Screening for gestational diabetes (GDM) at 24-28 wk of gestation is recommended in women who do not have previous history of diabetes, as GDM remains asymptomatic11. A history of GDM carries a high risk for developing diabetes.
There is no single gene that “causes” type 1 diabetes. Instead, there are a large number of inherited factors that may increase an individual’s likelihood of developing diabetes. This is known as multifactorial inheritance. The genes implicated in the development of type 1 diabetes mellitus control the human leukocyte antigen (HLA) system. This system is involved in the complex process of identifying cells which are a normal part of the body, and distinguishing them from foreign cells, such as those of bacteria or viruses. In an autoimmune disease such as diabetes mellitus, this system makes a mistake in identifying the normal ‘self’ cells as ‘foreign’, and attacks the body.  
No single environmental trigger has been identified as causing diabetes mellitus, however both infectious agents and dietary factors are thought to be important. Various viruses have been implicated in the development of type I DM. They may act by initiating or modifying the autoimmune process. In particular, the rubella virus and coxsackie viruses have been closely studied. In particular, congenital rubella infection has shown direct relationships with the development of type 1 diabetes mellitus. This is presumably due to the virus (or antibodies against it) damaging the beta cells of the pancreas. Some research has looked at dietary factors that may be associated with type 1 diabetes. In particular, cow’s milk proteins (such as bovine serum albumin) which may have some similarities to pancreatic islet cell markers may be able to trigger the autoimmune process. Other chemicals including nitrosamines have been identified as causes of diabetes mellitus in animal models, but not in humans.
Type 2 diabetes is often treated with oral medication because many people with this type of diabetes make some insulin on their own. The pills people take to control type 2 diabetes do not contain insulin. Instead, medications such as metformin, sulfonylureas, alpha-glucosidase inhibitors and many others are used to make the insulin that the body still produces more effective.
This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.
The good news is that if you have diabetes, you have a great amount of control in managing your disease. Although it can be difficult to manage a disease on a daily basis, the resources and support for people with diabetes is endless. It's important for you to receive as much education as possible so that you can take advantage of all the good information that is out there (and weed out the bad).
What does the research say about proactive type 2 diabetes management? Research shows that proactive management can pay off in fewer complications down the road. In the landmark UKPDS study, 5,102 patients newly diagnosed with type 2 diabetes were followed for an average of 10 years to determine whether intensive use of blood glucose-lowering drugs would result in health benefits. Tighter average glucose control (an A1c of 7.0% vs. an A1c of 7.9%) reduced the rate of complications in the eyes, kidneys, and nervous system, by 25%. For every percentage point decrease in A1c (e.g., from 9% to 8%), there was a 25% reduction in diabetes-related deaths, and an 18% reduction in combined fatal and nonfatal heart attacks.

Sequelae. The long-term consequences of diabetes mellitus can involve both large and small blood vessels throughout the body. That in large vessels is usually seen in the coronary arteries, cerebral arteries, and arteries of the lower extremities and can eventually lead to myocardial infarction, stroke, or gangrene of the feet and legs. atherosclerosis is far more likely to occur in persons of any age who have diabetes than it is in other people. This predisposition is not clearly understood. Some believe that diabetics inherit the tendency to develop severe atherosclerosis as well as an aberration in glucose metabolism, and that the two are not necessarily related. There is strong evidence to substantiate the claim that optimal control will mitigate the effects of diabetes on the microvasculature, particularly in the young and middle-aged who are at greatest risk for developing complications involving the arterioles. Pathologic changes in the small blood vessels serving the kidney lead to nephrosclerosis, pyelonephritis, and other disorders that eventually result in renal failure. Many of the deaths of persons with type 1 diabetes are caused by renal failure.

Type 2 diabetes is mainly caused by insulin resistance. This means no matter how much or how little insulin is made, the body can't use it as well as it should. As a result, glucose can't be moved from the blood into cells. Over time, the excess sugar in the blood gradually poisons the pancreas causing it to make less insulin and making it even more difficult to keep blood glucose under control.
Diabetes means your blood glucose, or blood sugar, levels are too high. With type 2 diabetes, the more common type, your body does not make or use insulin well. Insulin is a hormone that helps glucose get into your cells to give them energy. Without insulin, too much glucose stays in your blood. Over time, high blood glucose can lead to serious problems with your heart, eyes, kidneys, nerves, and gums and teeth.
The typical symptoms of diabetes mellitus are the three “polys:” polyuria, polydipsia, and polyphagia. Because of insulin deficiency, the assimilation and storage of glucose in muscle adipose tissues, and the liver is greatly diminished. This produces an accumulation of glucose in the blood and creates an increase in its osmolarity. In response to this increased osmotic pressure there is depletion of intracellular water and osmotic diuresis. The water loss creates intense thirst and increased urination. The increased appetite (polyphagia) is not as clearly understood. It may be the result of the body's effort to increase its supply of energy foods even though eating more carbohydrates in the absence of sufficient insulin does not meet the energy needs of the cells.
Apart from severe DKA or hypoglycemia, type 1 diabetes mellitus has little immediate morbidity. The risk of complications relates to diabetic control. With good management, patients can expect to lead full, normal, and healthy lives. Nevertheless, the average life expectancy of a child diagnosed with type 1 diabetes mellitus has been variously suggested to be reduced by 13-19 years, compared with their nondiabetic peers. [34]
Is type 2 diabetes serious? Type 2 diabetes is not a death sentence, but it is a very serious disease that demands attention and careful monitoring. There is no such thing as ‘mild’ diabetes. Elevated glucose levels can damage the nervous system, blood vessels, eyes, heart, and kidneys. These complications really impact quality of life (through blindness, amputations, dialysis etc). They also significantly increase the chance of a stroke or heart attack. Managing blood glucose levels immediately, along with other health risk factors (e.g., cholesterol, blood pressure, weight), is necessary for preventing these complications. Losing even a small amount of weight and keeping it off can also improve glucose control as well as have other clinical benefits (read more tips on managing diet and exercise below for more on weight loss). Keep in mind that better diabetes management also has benefits in the here and now – mood and energy levels are adversely affected when your glucose levels are high. 
High blood glucose sets up a domino effect of sorts within your body. High blood sugar leads to increased production of urine and the need to urinate more often. Frequent urination causes you to lose a lot of fluid and become dehydrated. Consequently, you develop a dry mouth and feel thirsty more often. If you notice that you are drinking more than usual, or that your mouth often feels dry and you feel thirsty more often, these could be signs of type 2 diabetes.