Diabetes mellitus is a group of metabolic diseases characterized by high blood sugar (glucose) levels, that result from defects in insulin secretion, or action, or both. Diabetes mellitus, commonly referred to as diabetes (as it will be in this article) was first identified as a disease associated with "sweet urine," and excessive muscle loss in the ancient world. Elevated levels of blood glucose (hyperglycemia) lead to spillage of glucose into the urine, hence the term sweet urine.

There are two major types of diabetes, called type 1 and type 2.
Type 1 diabetes was also called insulin dependent diabetes mellitus (IDDM), or juvenile onset diabetes mellitus. In type 1 diabetes, the pancreas undergoes an autoimmune attack by the body itself, and is rendered incapable of making insulin.

Type 2 diabetes was also 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.

•    Insufficient production of insulin (either absolutely or relative to the body's needs)
•    Production of defective insulin (which is uncommon),
•    The inability of cells to use insulin properly and efficiently leads to hyperglycemia and diabetes

•    The early symptoms of untreated diabetes are related to elevated blood sugar levels, and loss of glucose in the urine. High amounts of glucose in the urine can cause increased urine output and lead to dehydration. Dehydration causes increased thirst and water consumption.
•    The inability of insulin to perform normally has effects on protein, fat and carbohydrate metabolism. Insulin is an anabolic hormone, that is, one that encourages storage of fat and protein.
•    A relative or absolute insulin deficiency eventually leads to weight loss despite an increase in appetite.
•    Some untreated diabetes patients also complain of fatigue, nausea and vomiting.
•    Patients with diabetes are prone to developing infections of the bladder, skin, and vaginal areas.
•    Fluctuations in blood glucose levels can lead to blurred vision. Extremely elevated glucose levels can lead to lethargy and coma.

The fasting blood glucose (sugar) test is the preferred way to diagnose diabetes. It is easy to perform and convenient. After the person has fasted overnight (at least 8 hours), a single sample of blood is drawn and sent to the laboratory for analysis. This can also be done accurately in a doctor's office using a glucose meter.

•    Normal fasting plasma glucose levels are less than 100 milligrams per deciliter (mg/dl).
•    Fasting plasma glucose levels of more than 126 mg/dl on two or more tests on different days indicate diabetes.
•    A random blood glucose test can also be used to diagnose diabetes. A blood glucose level of 200 mg/dl or higher indicates diabetes.

Sulfonylureas

• Glipizide
• Glyburide
• Glimepiride
• Gliclazide

Biguanides

• Metformin
• Thiazolidinediones
• Rosiglitazone
• Pioglitazone
• Troglitazone

Alpha-glucosidase inhibitors

•    Miglitol
•    Acarbose
Insulin is used medically to treat some forms of diabetes mellitus. Patients with Type 1 diabetes mellitus depend on external insulin(most commonly injected subcutaneously) for their survival because the hormone is no longer produced internally.

•    Cardiovascular disease. Diabetes dramatically increases the risk of various cardiovascular problems, including coronary artery disease with chest pain (angina), heart attack, stroke and narrowing of arteries (atherosclerosis). If you have diabetes, you are twice as likely to have heart disease or stroke.
•    Nerve damage (neuropathy). Excess sugar can injure the walls of the tiny blood vessels (capillaries) that nourish your nerves, especially in the legs. This can cause tingling, numbness, burning or pain that usually begins at the tips of the toes or fingers and over a period of months or years gradually spreads upward. Left untreated, you could lose all sense of feeling in the affected limbs
•    Kidney damage (nephropathy). The kidneys contain millions of tiny blood vessel clusters (glomeruli) that filter waste from your blood. Diabetes can damage this delicate filtering system. Severe damage can lead to kidney failure or irreversible end-stage kidney disease, requiring dialysis or a kidney transplant.
•    Eye damage. Diabetes can damage the blood vessels of the retina (diabetic retinopathy), potentially leading to blindness.
•    Foot damage. Nerve damage in the feet or poor blood flow to the feet increases the risk of various foot complications. Left untreated, cuts and blisters can become serious infections. Severe damage might require toe, foot or even leg amputation.
•    Skin and mouth conditions. Diabetes may leave you more susceptible to skin problems, including bacterial infections, fungal infections and itching. Gum infections also may be a concern, especially if you have a history of poor dental hygiene.
•    Bone and joint problems. Diabetes may put you at risk of bone and joint problems such as osteoporosis.

Type 1 diabetes can't be prevented. However, the same healthy lifestyle choices that help treat prediabetes, type 2 diabetes and gestational diabetes can help prevent them.

•    Eat healthy foods: Choose foods low in fat and calories. Focus on fruits, vegetables and whole grains. Strive for variety to prevent boredom.
•    Get more physical activity: Aim for 30 minutes of moderate physical activity a day. Take a brisk daily walk. Ride your bike. Swim laps. If you can't fit in a long workout, break it up into smaller sessions spread throughout the day.
•    Lose excess weight:  If you're overweight, losing even 5 percent of your body weight — for example, 10 pounds (4.5 kilograms) if you weigh 200 pounds (90.7 kilograms) — can reduce the risk of diabetes. To keep your weight in a healthy range, focus on permanent changes to your eating and exercise habits. Motivate yourself by remembering the benefits of losing weight, such as a healthier heart, more energy and improved self-esteem.