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Type 1 and type 2 diabetes were identified as separate conditions for the first time by the Indian physicians Sushruta and Charaka in 400–500 CE with type 1 associated with youth and type 2 with being overweight.[108] The term "mellitus" or "from honey" was added by the Briton John Rolle in the late 1700s to separate the condition from diabetes insipidus, which is also associated with frequent urination.[108] Effective treatment was not developed until the early part of the 20th century, when Canadians Frederick Banting and Charles Herbert Best isolated and purified insulin in 1921 and 1922.[108] This was followed by the development of the long-acting insulin NPH in the 1940s.[108]
WELL-CONTROLLED DIABETES MELLITUS: Daily blood sugar abstracted from the records of a patient whose DM is well controlled (hemoglobin A1c=6.4). The average capillary blood glucose level is 104 mg/dL, and the standard deviation is 19. Sixty-five percent of the readings are between 90 and 140 mg/dL; the lowest blood sugar is 67 mg/dL (on April 15) and the highest is about 190 (on March 21).
After a diagnosis of diabetes mellitus has been made, and treatment with insulin therapy has begun, a so-called ‘honeymoon stage’ may develop. This stage is characterised by a reduction in insulin requirements which may last from weeks to months. Some patients may require no insulin at all. This stage is always transient (short-lasting) and is due to production of insulin by the remaining surviving pancreatic beta cells. Eventually, these cells will be destroyed by the on-going auto-immune process, and the patient will be dependent on exogenous (artificial) insulin.

American Diabetes Association Joslin Diabetes Center Mayo Clinic International Diabetes Federation Canadian Diabetes Association National Institute of Diabetes and Digestive and Kidney Diseases Diabetes Daily American Heart Association Diabetes Forecast Diabetic Living American Association of Clinical Endocrinologists European Association for the Study of Diabetes

Type 1 diabetes is partly inherited, with multiple genes, including certain HLA genotypes, known to influence the risk of diabetes. In genetically susceptible people, the onset of diabetes can be triggered by one or more environmental factors,[41] such as a viral infection or diet. Several viruses have been implicated, but to date there is no stringent evidence to support this hypothesis in humans.[41][42] Among dietary factors, data suggest that gliadin (a protein present in gluten) may play a role in the development of type 1 diabetes, but the mechanism is not fully understood.[43][44]
Progression toward type 2 diabetes may even be self-perpetuating. Once a person begins to become insulin resistant, for whatever reason, things may snowball from there. The increased levels of circulating insulin required to compensate for resistance encourage the body to pack on pounds. That extra weight will in turn make the body more insulin resistant. Furthermore, the heavier a person is, the more difficult it can be to exercise, continuing the slide toward diabetes.
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. 
Previously, CGMs required frequent calibration with fingerstick glucose testing. Also their results were not accurate enough so that people always had to do a fingerstick to verify a reading on their CGM before calculating a dose of insulin (for example before meals or to correct a high blood sugar). However, recent technological advances have improved CGMs. One professional CGM can be worn for up to 14 days without calibration. Another personal CGM can be used to guide insulin dosing without confirmation by fingerstick glucose. Finally, there are now systems in which the CGM device communicates with insulin pumps to either stop delivery of insulin when blood glucose is dropping (threshold suspend), or to give daily insulin (hybrid closed loop system).
It is especially important that persons with diabetes who are taking insulin not skip meals; they must also be sure to eat the prescribed amounts at the prescribed times during the day. Since the insulin-dependent diabetic needs to match food consumption to the available insulin, it is advantageous to increase the number of daily feedings by adding snacks between meals and at bedtime.

Because people with type 2 diabetes produce some insulin, ketoacidosis does not usually develop even when type 2 diabetes is untreated for a long time. Rarely, the blood glucose levels become extremely high (even exceeding 1,000 mg/dL). Such high levels often happen as the result of some superimposed stress, such as an infection or drug use. When the blood glucose levels get very high, people may develop severe dehydration, which may lead to mental confusion, drowsiness, and seizures, a condition called hyperosmolar hyperglycemic state. Currently, many people with type 2 diabetes are diagnosed by routine blood glucose testing before they develop such severely high blood glucose levels.
So what determines where fat is stored, and thus a person's propensity for insulin resistance and type 2 diabetes? Well, just having more fat in the body increases the risk that some of it will get misplaced. But exercise may also have a role in fat placement. Exercise is known to reduce insulin resistance; one way it may do this is by burning fat out of the muscle. Because of this, getting enough exercise may stave off type 2 in some cases. Genes may also help orchestrate the distribution of fat in the body, which illustrates how lifestyle and genetics interact.
A 2018 study suggested that three types should be abandoned as too simplistic.[57] It classified diabetes into five subgroups, with what is typically described as type 1 and autoimmune late-onset diabetes categorized as one group, whereas type 2 encompasses four categories. This is hoped to improve diabetes treatment by tailoring it more specifically to the subgroups.[58]

Studies in type 1 patients have shown that in intensively treated patients, diabetic eye disease decreased by 76%, kidney disease decreased by 54%, and nerve disease decreased by 60%. More recently the EDIC trial has shown that type 1 diabetes is also associated with increased heart disease, similar to type 2 diabetes. However, the price for aggressive blood sugar control is a two to three fold increase in the incidence of abnormally low blood sugar levels (caused by the diabetes medications). For this reason, tight control of diabetes to achieve glucose levels between 70 to120 mg/dl is not recommended for children under 13 years of age, patients with severe recurrent hypoglycemia, patients unaware of their hypoglycemia, and patients with far advanced diabetes complications. To achieve optimal glucose control without an undue risk of abnormally lowering blood sugar levels, patients with type 1 diabetes must monitor their blood glucose at least four times a day and administer insulin at least three times per day. In patients with type 2 diabetes, aggressive blood sugar control has similar beneficial effects on the eyes, kidneys, nerves and blood vessels.
Glycated hemoglobin (A1C) test. This blood test indicates your average blood sugar level for the past two to three months. It measures the percentage of blood sugar attached to hemoglobin, the oxygen-carrying protein in red blood cells. The higher your blood sugar levels, the more hemoglobin you'll have with sugar attached. An A1C level of 6.5 percent or higher on two separate tests indicates you have diabetes. A result between 5.7 and 6.4 percent is considered prediabetes, which indicates a high risk of developing diabetes. Normal levels are below 5.7 percent.
People with type 2 diabetes have insulin resistance, which means the body cannot use insulin properly to help glucose get into the cells. In people with type 2 diabetes, insulin doesn’t work well in muscle, fat, and other tissues, so your pancreas (the organ that makes insulin) starts to put out a lot more of it to try and compensate. "This results in high insulin levels in the body,” says Fernando Ovalle, MD, director of the multidisciplinary diabetes clinic at the University of Alabama in Birmingham. This insulin level sends signals to the brain that your body is hungry.