What is it?
Note: This article addresses diabetes mellitus, not diabetes insipidus. Although the two share the same reference term "diabetes" (which means increased urine production), diabetes insipidus is much rarer and has a different underlying cause.
Diabetes mellitus is a condition in which the level of glucose (sugar) in an individual's blood becomes too high because the body cannot use it properly. This results either from an inability to produce insulin or because the individual's body has become resistant to the insulin produced. About 2.8 million people in the United Kingdom (4.45% of the population) are known to have diabetes and a further ¾ million may have the condition and not know it. Insulin is a hormone, produced by beta cells of the pancreas, which controls the movement of glucose into most of the body's cells and maintains blood glucose levels within a narrow concentration range. Most tissues in the body rely on glucose for energy production, and all but a few - such as the brain and nervous system - are entirely reliant on insulin to deliver this essential fuel. Diabetes disrupts the normal balance between insulin and glucose. Usually after a meal, carbohydrates are broken down into glucose and other simple sugars. This causes blood glucose levels to rise and stimulates the pancreas to release insulin into the bloodstream. Insulin allows glucose into the cells, where it also promotes storage of excess glucose - either as glycogen in the liver or as triglycerides in adipose (fat) cells.
If there is insufficient or ineffective insulin, glucose levels remain high in the bloodstream and the body's cells "starve." Since glucose is not available to the cells with severe insulin deficiency, the body may attempt to provide an alternate energy source by breakind down fatty acids from fat cells. This less efficient process leads to a build-up of ketones (by-products that result from the use of fat as an alternative energy source when glucose is unavailable) and upsets the body’s acid-base balance, producing a state known as ketoacidosis.
This can cause both short term and long term problems depending on the severity of the imbalance. In the short term it can upset the body's electrolyte balance, causing dehydration as high blood glucose levels increase the amount of urine produced. If unchecked, this can eventually lead to loss of consciousness, kidney failure and death. In the longer term, sustained high glucose levels can damage blood vessels, nerves, and organs throughout the body, contributing to other problems such as high blood pressure, heart disease, kidney failure and loss of vision in addition to diabetes.