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Diabetes Mellitus Type 2

Diabetes mellitus type 2 – formerly non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes – is a metabolic disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency.[2] Diabetes is often initially managed by increasing exercise and dietary modification. If the condition progresses, medications may be needed. Often affecting the obese, diabetes requires patients to routinely check their blood sugar.

Unlike type 1 diabetes, there is very little tendency toward ketoacidosis although it is not unheard of.[3] One effect that can occur is nonketonic hyperglycemia. Long-term complications from high blood sugar can include increased risk of heart attacks, strokes, diabetic retinopathy where eye sight is affected, and kidney failure. For extreme cases, circulation of limbs is affected, potentially requiring amputation. Loss of hearing, eyesight, and cognitive ability has also been linked to this condition.

Signs and Symptoms

The classic symptoms of diabetes are polyuria (frequent urination), polydipsia (increased thirst), polyphagia (increased hunger), fatigue and weight loss.[4] Type 2 diabetes has been associated with an increased risk of cognitive dysfunction and dementia through disease processes such as Alzheimer's disease and vascular dementia. Researchers have shown that reduced glucose tolerance has deleterious effects on memory in the elderly, and concomitant hippocampal atrophy.[5]


Type 2 diabetes is due to a combination of lifestyle and genetic factors.[6][7] Recently, intrauterine growth restriction (IUGR) or prenatal undernutrition (macro- and micronutrient) was identified as another probable factor [8] A clue for this concept was the Dutch Hunger Winter (1944–1945) during World War II, and the pioneering work of Professor Barker.


A number of lifestyle factors are known to be important to the development of type 2 diabetes. In one study, those who had high levels of physical activity, a healthy diet, did not smoke, and consumed alcohol in moderation had an 82% lower rate of diabetes. When a normal weight was included, the rate was 89% lower. In this study, a healthy diet was defined as one high in fiber, with a high polyunsaturated to saturated fat ratio, and a lower mean glycemic index.[9] Obesity has been found to contribute to approximately 55% of cases of type 2 diabetes,[10] and decreasing consumption of saturated fats and trans fatty acids while replacing them with unsaturated fats may decrease the risk.[6] The increased rate of childhood obesity between the 1960s and 2000s is believed to have led to the increase in type 2 diabetes in children and adolescents.[11] Dietary fat intake is linked to diabetes risk.[12]

A 2010 meta-analysis of eleven studies involving 310,819 participants and 15,043 cases of type 2 diabetes[13] found that "SSBs [sugar-sweetened beverages] may increase the risk of metabolic syndrome and type 2 diabetes not only through obesity but also by increasing dietary glycemic load, leading to insulin resistance, ?-cell dysfunction, and inflammation."

Environmental toxins may contribute to recent increases in the rate of type 2 diabetes. A weak positive correlation has been found between the concentration in the urine of bisphenol A, a constituent of some plastics, and the incidence of type 2 diabetes.[14]

Medical conditions

There are many factors which can potentially give rise to, or exacerbate, type 2 diabetes. These include obesity, hypertension, elevated cholesterol (combined hyperlipidemia), and with the condition often termed metabolic syndrome (it is also known as Syndrome X, Reavan's syndrome, or CHAOS). Other causes include acromegaly, Cushing's syndrome, thyrotoxicosis, pheochromocytoma, chronic pancreatitis, cancer, and drugs. Additional factors found to increase the risk of type 2 diabetes include aging,[15] high-fat diets[16] and a less active lifestyle.[17]

Subclinical Cushing's syndrome (cortisol excess) may be associated with type 1 diabetes.[18] The percentage of subclinical Cushing's syndrome in the diabetic population is about 9%.[19] Diabetic patients with a pituitary microadenoma can improve insulin sensitivity by removal of these microadenomas.[20]

Hypogonadism is often associated with cortisol excess, and testosterone deficiency is also associated with type 2 diabetes,[21][22] even if the exact mechanism by which testosterone improves insulin sensitivity is still not known.


There is also a strong inheritable genetic connection in type 2 diabetes: having relatives (especially first degree) with type 2 increases risks of developing type 2 diabetes substantially. Genetic risk for type 2 diabetes decreased as humans first began migrating around the world, implying a strong environmental component has affected the genetic-basis of type 2 diabetes.[23][24] In addition, there is also a mutation to the Islet Amyloid Polypeptide gene that results in an earlier onset, more severe, form of diabetes.[25][26]

About 55 percent of type 2 diabetes patients are obese at diagnosis[27] —chronic obesity leads to increased insulin resistance that can develop into type 2 diabetes, most likely because adipose tissue (especially that in the abdomen around internal organs) is a source of several chemical signals, hormones and cytokines, to other tissues. Inflammatory cytokines for example may activate the NF-?B pathway which has been linked to the development of insulin resistance.[28]

Other research shows that type 2 diabetes causes obesity as an effect of the changes in metabolism and other deranged cell behavior attendant on insulin resistance.[29]

However, environmental factors (almost certainly diet and weight) play a large part in the development of type 2 diabetes in addition to any genetic component. This can be seen from the adoption of the type 2 diabetes epidemiological pattern in those who have moved to a different environment as compared to the same genetic pool who have not. Immigrants to Western developed countries, for instance, as compared to lower incidence countries of origins.[30] Such developments can also be found in environments which have had a recent increase in social wealth, increasingly common throughout Asia.

There is a stronger inheritance pattern for type 2 diabetes. Those with first-degree relatives with type 2 diabetes have a much higher risk of developing type 2 diabetes, increasing with the number of those relatives. Concordance among monozygotic twins is close to 100%, and about 25% of those with the disease have a family history of diabetes. Genes significantly associated with developing type 2 diabetes, include TCF7L2, PPARG, FTO, KCNJ11, NOTCH2, WFS1, CDKAL1, IGF2BP2, SLC30A8, JAZF1, and HHEX.[31][32] KCNJ11 (potassium inwardly rectifying channel, subfamily J, member 11), encodes the islet ATP-sensitive potassium channel Kir6.2, and TCF7L2 (transcription factor 7–like 2) regulates proglucagon gene expression and thus the production of glucagon-like peptide-1.[33] Moreover, obesity (which is an independent risk factor for type 2 diabetes) is strongly inherited.[34]

Monogenic forms, e.g., MODY, constitute 1–5 % of all cases.[35]

Various hereditary conditions may feature diabetes, for example myotonic dystrophy and Friedreich's ataxia. Wolfram's syndrome is an autosomal recessive neurodegenerative disorder that first becomes evident in childhood. It consists of diabetes insipidus, diabetes mellitus, optic atrophy, and deafness, hence the acronym DIDMOAD.[36]

Gene expression promoted by a diet of fat and glucose, as well as high levels of inflammation related cytokines found in the obese, results in cells that "produce fewer and smaller mitochondria than is normal," and are thus prone to insulin resistance.[37]


Insulin resistance means that body cells do not respond appropriately when insulin is present.[38]

This is a more complex problem than type 1, but is sometimes easier to treat, especially in the early years when insulin is often still being produced internally. Severe complications can result from improperly managed type 2 diabetes, including renal failure, erectile dysfunction, blindness, slow healing wounds (including surgical incisions), and arterial disease, including coronary artery disease. The onset of type 2 diabetes has been most common in middle age and later life, although it is being more frequently seen in adolescents and young adults due to an increase in child obesity and inactivity. A type of diabetes called MODY is increasingly seen in adolescents, but this is classified as a diabetes due to a specific cause and not as type 2 diabetes.

In the 2008 Banting Lecture of the American Diabetes Association, DeFronzo enumerates eight main pathophysiological factors in the type 2 diabetic organism [39]

Diabetes mellitus with a known etiology, such as secondary to other diseases, known gene defects, trauma or surgery, or the effects of drugs, is more appropriately called secondary diabetes mellitus or diabetes due to a specific cause. Examples include diabetes mellitus such as MODY or those caused by hemochromatosis, pancreatic insufficiencies, or certain types of medications (e.g., long-term steroid use).

Recent studies of pancreatic beta cells have indicated a molecular connection between diet, obesity that involves the role of fat in activating a pathway to type 2 diabetes.[40] In this mechanism, loss of beta cell glucose sensing contributes substantially to the early manifestation of diabetes, and beta cell dysfunction is responsible for the onset and severity of multiple systemic disease signs including impaired glucose tolerance, hyperglycemia, hepatic steatosis and insulin resistance in muscle and adipose cells. Previous work published in past decades by the laboratories of Roger Unger, Jerrold Olefsky, and Bernard Thorens alluded to the possibility of the importance of beta cell function and glucose sensing in these disease signs. This mechanism of beta cell dysfunction may be contributing substantially to the current epidemic of type 2 diabetes.

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