Diabetes mellitus results mainly from a deficiency or diminished effectiveness of insulin that is normally produced by the beta cells of the pancreas. It is characterised by high blood sugar, altered sugar and glucose metabolism and this affects blood vessels and causes several organ damage. Causes of diabetes can be classified according to the types of diabetes.
The term "diabetes" or "to pass through" was first used in 230 BCE by the Greek Apollonius of Memphis.[108] The disease was considered rare during the time of the Roman empire, with Galen commenting he had only seen two cases during his career.[108] This is possibly due to the diet and lifestyle of the ancients, or because the clinical symptoms were observed during the advanced stage of the disease. Galen named the disease "diarrhea of the urine" (diarrhea urinosa).[110]
There are other factors that also fall into the category of environmental (as opposed to genetic) causes of diabetes. Certain injuries to the pancreas, from physical trauma or from drugs, can harm beta cells, leading to diabetes. Studies have also found that people who live in polluted areas are prone to type 2, perhaps because of inflammation. And an alternate theory of insulin resistance places the blame on damage caused by inflammation. Age also factors into type 2; beta cells can wear out over time and become less capable of producing enough insulin to overcome insulin resistance, which is why older people are at greater risk of type 2.
Type 2 Diabetes: Accounting for 90 to 95 percent of those with diabetes, type 2 is the most common form. Usually, it's diagnosed in adults over age 40 and 80 percent of those with type 2 diabetes are overweight. Because of the increase in obesity, type 2 diabetes is being diagnosed at younger ages, including in children. Initially in type 2 diabetes, insulin is produced, but the insulin doesn't function properly, leading to a condition called insulin resistance. Eventually, most people with type 2 diabetes suffer from decreased insulin production.
Another less common form is gestational diabetes, a temporary condition that occurs during pregnancy. Depending on risk factors, between 3% to 13% of Canadian women will develop gestational diabetes which can be harmful for the baby if not controlled. The problem usually clears up after delivery, but women who have had gestational diabetes have a higher risk of developing type 2 diabetes later in life.
Per the WHO, people with fasting glucose levels from 6.1 to 6.9 mmol/l (110 to 125 mg/dl) are considered to have impaired fasting glucose.[67] people with plasma glucose at or above 7.8 mmol/l (140 mg/dl), but not over 11.1 mmol/l (200 mg/dl), two hours after a 75 gram oral glucose load are considered to have impaired glucose tolerance. Of these two prediabetic states, the latter in particular is a major risk factor for progression to full-blown diabetes mellitus, as well as cardiovascular disease.[68] The American Diabetes Association (ADA) since 2003 uses a slightly different range for impaired fasting glucose of 5.6 to 6.9 mmol/l (100 to 125 mg/dl).[69]
Type 2 diabetes is typically a chronic disease associated with a ten-year-shorter life expectancy.[10] This is partly due to a number of complications with which it is associated, including: two to four times the risk of cardiovascular disease, including ischemic heart disease and stroke; a 20-fold increase in lower limb amputations, and increased rates of hospitalizations.[10] In the developed world, and increasingly elsewhere, type 2 diabetes is the largest cause of nontraumatic blindness and kidney failure.[24] It has also been associated with an increased risk of cognitive dysfunction and dementia through disease processes such as Alzheimer's disease and vascular dementia.[25] Other complications include acanthosis nigricans, sexual dysfunction, and frequent infections.[23]
A chronic metabolic disorder marked by hyperglycemia. DM results either from failure of the pancreas to produce insulin (type 1 DM) or from insulin resistance, with inadequate insulin secretion to sustain normal metabolism (type 2 DM). Either type of DM may damage blood vessels, nerves, kidneys, the retina, and the developing fetus and the placenta during pregnancy. Type 1 or insulin-dependent DM has a prevalence of just 0.3 to 0.4%. Type 2 DM (formerly called adult-onset DM) has a prevalence in the general population of 6.6%. In some populations (such as older persons, Native Americans, African Americans, Pacific Islanders, Mexican Americans), it is present in nearly 20% of adults. Type 2 DM primarily affects obese middle-aged people with sedentary lifestyles, whereas type 1 DM usually occurs in children, most of whom are active and thin, although extremely obese children are now being diagnosed with type 2 diabetes as well. See: table; dawn phenomenon; insulin; insulin pump; insulin resistance; diabetic polyneuropathy; Somogyi phenomenon
Can type 2 diabetes be cured? In the early stages of type 2 diabetes, it is possible to manage the diabetes to a level where symptoms go away and A1c reaches a normal level – this effectively “reverses” the progression of type 2 diabetes. According to research from Newcastle University, major weight loss can return insulin secretion to normal in people who had type 2 diabetes for four years or less. Indeed, it is commonly believed that significant weight loss and building muscle mass is the best way to reverse type 2 diabetes progression. However, it is important to note that reversing diabetes progression is not the same as curing type 2 diabetes – people still need to monitor their weight, diet, and exercise to ensure that type 2 diabetes does not progress. For many people who have had type 2 diabetes for a longer time, the damage to the beta cells progresses to the point at which it will never again be possible to make enough insulin to correctly control blood glucose, even with dramatic weight loss. But even in these people, weight loss is likely the best way to reduce the threat of complications.

Diabetes mellitus is a diagnostic term for a group of disorders characterized by abnormal glucose homeostasis resulting in elevated blood sugar. It is among the most common of chronic disorders, affecting up to 5–10% of the adult population of the Western world. The prevalence of diabetes is increasing dramatically; it has been estimated that the worldwide prevalence will increase by more than 50% between the years 2000 and 2030 (Wild et al., 2004). It is clearly established that diabetes mellitus is not a single disease, but a genetically heterogeneous group of disorders that share glucose intolerance in common. The concept of genetic heterogeneity (i.e. that different genetic and/or environmental etiologic factors can result in similar phenotypes) has significantly altered the genetic analysis of this common disorder.
Along with following your diabetes care plan, you may need diabetes medicines, which may include pills or medicines you inject under your skin, such as insulin. Over time, you may need more than one diabetes medicine to manage your blood glucose. Even if you don’t take insulin, you may need it at special times, such as during pregnancy or if you are in the hospital. You also may need medicines for high blood pressure, high cholesterol, or other conditions.
The roots of type 2 diabetes remain in insulin resistance and pancreatic failure, and the blame for the current diabetes epidemic lies in an overall dietary pattern emphasizing meat, dairy products, and fatty foods, aided and abetted by sugary foods and beverages, rather than simply in sugar alone. A diet emphasizing vegetables, fruits, whole grains, and legumes and avoiding animal products helps prevent diabetes and improves its management when it has been diagnosed. 
All you need to know about insulin sensitivity factor Insulin sensitivity factor is a measurement that describes how blood sugar levels are affected by taking 1 unit of insulin. It can help a person with type 1 diabetes regulate their blood sugar levels. Learn more about what insulin sensitivity factor is, who should test and when, and what the results mean. Read now
Diabetes can be looked for by testing a urine sample for sugar but for a diagnosis, a blood sample is required. This may be a simple measurement of the sugar level, usually fasting. Alternatively, a test called an HbA1c can be used which estimates sugar levels over the past couple of months. If someone has typical symptoms of diabetes, only a single abnormal test is required. Where there are no symptoms, a second confirmatory test is required. Sometimes, particularly in pregnancy, a glucose tolerance test is performed which involves blood tests before and 2 hours after a sugary drink.

Those dark patches on your skin could be more serious than a blotchy tan. In fact, they might be the first sign of diabetes. This darkening of the skin, which usually occurs on the hands and feet, in folds of skin, along the neck, and in a person’s groin and armpits, called acanthosis nigricans, often occurs when insulin levels are high. The high insulin levels in your blood can increase your body’s production of skin cells, many of which have increased pigmentation, giving skin a darkened appearance.

Type 2 diabetes was also previously referred to as non-insulin dependent diabetes mellitus (NIDDM), or adult-onset diabetes mellitus (AODM). In type 2 diabetes, patients can still produce insulin, but do so relatively inadequately for their body's needs, particularly in the face of insulin resistance as discussed above. In many cases this actually means the pancreas produces larger than normal quantities of insulin. A major feature of type 2 diabetes is a lack of sensitivity to insulin by the cells of the body (particularly fat and muscle cells).
Most cases of diabetes involve many genes, with each being a small contributor to an increased probability of becoming a type 2 diabetic.[10] If one identical twin has diabetes, the chance of the other developing diabetes within his lifetime is greater than 90%, while the rate for nonidentical siblings is 25–50%.[13] As of 2011, more than 36 genes had been found that contribute to the risk of type 2 diabetes.[37] All of these genes together still only account for 10% of the total heritable component of the disease.[37] The TCF7L2 allele, for example, increases the risk of developing diabetes by 1.5 times and is the greatest risk of the common genetic variants.[13] Most of the genes linked to diabetes are involved in beta cell functions.[13]

Jump up ^ Boussageon, R; Bejan-Angoulvant, T; Saadatian-Elahi, M; Lafont, S; Bergeonneau, C; Kassaï, B; Erpeldinger, S; Wright, JM; Gueyffier, F; Cornu, C (2011-07-26). "Effect of intensive glucose lowering treatment on all cause mortality, cardiovascular death, and microvascular events in type 2 diabetes: meta-analysis of randomised controlled trials". The BMJ. 343: d4169. doi:10.1136/bmj.d4169. PMC 3144314. PMID 21791495.

Another diabetes-related sexual dysfunction symptom in men is reduced amounts of ejaculation, or retrograde ejaculation. Retrograde ejaculation is a condition in which the semen goes into the bladder, rather than out of the body through the urethra. Diabetes and damage to the blood vessels causes nerve damage to the muscles that control the bladder and urethra, which results in this problem.

Along with following your diabetes care plan, you may need diabetes medicines, which may include pills or medicines you inject under your skin, such as insulin. Over time, you may need more than one diabetes medicine to manage your blood glucose. Even if you don’t take insulin, you may need it at special times, such as during pregnancy or if you are in the hospital. You also may need medicines for high blood pressure, high cholesterol, or other conditions.

Despite our efforts, patients are still likely to suffer myocardial infarction. The Diabetes mellitus, Insulin Glucose infusion in Acute Myocardial Infarction (DIGAMI) study236,237 reported on treating subjects with acute myocardial infarction and either diabetes or raised random plasma glucose (i.e., not necessarily diabetic) with either an intensive insulin infusion and then a four-times daily insulin regimen or conventional treatment. Over a mean follow-up of 3.4 years, there was a 33% death rate in the treatment group compared with a 44% death rate in the control group, an absolute reduction in mortality of 11%. The effect was greatest among the subgroup without previous insulin treatment and at a low cardiovascular risk. Evidence is continuing to accumulate that the diabetic person should have a glucose/insulin infusion after a myocardial infarction.

The major eye complication of diabetes is called diabetic retinopathy. Diabetic retinopathy occurs in patients who have had diabetes for at least five years. Diseased small blood vessels in the back of the eye cause the leakage of protein and blood in the retina. Disease in these blood vessels also causes the formation of small aneurysms (microaneurysms), and new but brittle blood vessels (neovascularization). Spontaneous bleeding from the new and brittle blood vessels can lead to retinal scarring and retinal detachment, thus impairing vision.

DM affects at least 16 million U.S. residents, ranks seventh as a cause of death in the United States, and costs the national economy over $100 billion yearly. The striking increase in the prevalence of DM in the U.S. during recent years has been linked to a rise in the prevalence of obesity. About 95% of those with DM have Type 2, in which the pancreatic beta cells retain some insulin-producing potential, and the rest have Type 1, in which exogenous insulin is required for long-term survival. In Type 1 DM, which typically causes symptoms before age 25, an autoimmune process is responsible for beta cell destruction. Type 2 DM is characterized by insulin resistance in peripheral tissues as well as a defect in insulin secretion by beta cells. Insulin regulates carbohydrate metabolism by mediating the rapid transport of glucose and amino acids from the circulation into muscle and other tissue cells, by promoting the storage of glucose in liver cells as glycogen, and by inhibiting gluconeogenesis. The normal stimulus for the release of insulin from the pancreas is a rise in the concentration of glucose in circulating blood, which typically occurs within a few minutes after a meal. When such a rise elicits an appropriate insulin response, so that the blood level of glucose falls again as it is taken into cells, glucose tolerance is said to be normal. The central fact in DM is an impairment of glucose tolerance of such a degree as to threaten or impair health. Long recognized as an independent risk factor for cardiovascular disease, DM is often associated with other risk factors, including disorders of lipid metabolism (elevation of very-low-density lipoprotein cholesterol and triglycerides and depression of high-density lipoprotein cholesterol), obesity, hypertension, and impairment of renal function. Sustained elevation of serum glucose and triglycerides aggravates the biochemical defect inherent in DM by impairing insulin secretion, insulin-mediated glucose uptake by cells, and hepatic regulation of glucose output. Long-term consequences of the diabetic state include macrovascular complications (premature or accelerated atherosclerosis with resulting coronary, cerebral, and peripheral vascular insufficiency) and microvascular complications (retinopathy, nephropathy, and neuropathy). It is estimated that half those with DM already have some complications when the diagnosis is made. The American Diabetes Association (ADA) recommends screening for DM for people with risk factors such as obesity, age 45 years or older, family history of DM, or history of gestational diabetes. If screening yields normal results, it should be repeated every 3 years. The diagnosis of DM depends on measurement of plasma glucose concentration. The diagnosis is confirmed when any two measurements of plasma glucose performed on different days yield levels at or above established thresholds: in the fasting state, 126 mg/dL (7 mmol/L); 2 hours postprandially (after a 75-g oral glucose load) or at random, 200 mg/dL (11.1 mmol/L). A fasting plasma glucose of 100-125 mg/dL (5.5-6.9 mmol/L) or a 2-hour postprandial glucose of 140-199 mg/dL (7.8-11 mmol/L) is defined as impaired glucose tolerance. People with impaired glucose tolerance are at higher risk of developing DM within 10 years. For such people, lifestyle modification such as weight reduction and exercise may prevent or postpone the onset of frank DM. Current recommendations for the management of DM emphasize education and individualization of therapy. Controlled studies have shown that rigorous maintenance of plasma glucose levels as near to normal as possible at all times substantially reduces the incidence and severity of long-term complications, particularly microvascular complications. Such control involves limitation of dietary carbohydrate and saturated fat; monitoring of blood glucose, including self-testing by the patient and periodic determination of glycosylated hemoglobin; and administration of insulin (particularly in Type 1 DM), drugs that stimulate endogenous insulin production (in Type 2 DM), or both. The ADA recommends inclusion of healthful carbohydrate-containing foods such as whole grains, fruits, vegetables, and low-fat milk in a diabetic diet. Restriction of dietary fat to less than 10% of total calories is recommended for people with diabetes, as for the general population. Further restriction may be appropriate for those with heart disease or elevated cholesterol or triglyceride levels. The ADA advises that high-protein, low-carbohydrate diets have no particular merit in long-term weight control or in maintenance of a normal plasma glucose level in DM. Pharmaceutical agents developed during the 1990s improve control of DM by enhancing responsiveness of cells to insulin, counteracting insulin resistance, and reducing postprandial carbohydrate absorption. Tailor-made insulin analogues produced by recombinant DNA technology (for example, lispro, aspart, and glargine insulins) have broadened the range of pharmacologic properties and treatment options available. Their use improves both short-term and long-term control of plasma glucose and is associated with fewer episodes of hypoglycemia. SEE ALSO insulin resistance
Over time, a prolonged exposure to high blood sugar can damage the nerves throughout the body — a condition called diabetic neuropathy. Some people may not have any symptoms of the damage, while others may notice numbness, tingling, or pain in the extremities. “At the beginning, [diabetic neuropathy] usually starts in the feet and then it progresses upward,” says Dr. Ovalle. Although most common in people who have had type 2 diabetes for 25 years or more, it can occur in people who have prediabetes as well. In some studies, almost 50 percent of unexplained peripheral neuropathy [in the extremities], whether painful or otherwise, turns out to be caused by prediabetes or diabetes, says Dr. Einhorn.