Types of diabetes

Type 1 diabetes

Type 1 diabetes is caused largely by the body's own immune systemThe organs specialised to fight infection. turning on itself; in other words, it is an 'autoimmuneAny condition caused by the body’s immune response against its own tissues.' condition.

Sometimes, type 1 diabetes is called early-onset or juvenile-onset diabetes because it is usually diagnosed in younger people, before the age of 40

Immune cells called lymphocytes enter the pancreas and destroy beta cellsThe cells of the pancreas where insulin is produced., the cells that produce insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels., over the course of many years. The other cells of the pancreas are not harmed. The symptoms of diabetes are seen only when 70 to 90 per cent of the beta cellsThe cells of the pancreas where insulin is produced. have been destroyed.[1,2]

The reduction in insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels. levels leads to high levels of glucoseA simple sugar that is an important source of energy in the body. in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid.. When bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. glucoseA simple sugar that is an important source of energy in the body. levels are high enough, glucoseA simple sugar that is an important source of energy in the body. is also excreted in the urine, drawing increased volumes of water with it.

This means that there is an increase in the amount of urine passed, which results in dehydrationWater deficiency in the body. and reduced salt levels. The symptoms of all this include fatigue, excess urine production, and increased thirst. There is also an increased the risk of genital infections.[1]

Insulin normally prevents fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. breakdown, as well as the breakdown of other compounds such as protein. When insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels. levels are low, fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. and muscleTissue made up of cells that can contract to bring about movement. breakdown is increased, causing wasting and weight loss.[1]

Sometimes, type 1 diabetes is called early-onset or juvenile-onset diabetes because it is usually diagnosed in younger people, before the age of 40. However, it can occur in people of any age.[3]

Type 2 diabetes

Type 2 diabetes usually affects an older age group, often people who are overweight or obese. It is mainly caused by the body becoming resistantA microbe, such as a type of bacteria, that is able to resist the effects of antibiotics or other drugs. to the actions of insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels..[1]

People with type 2 diabetes may feel tired but have no other symptoms at all; because of this, many people with type 2 diabetes do not know they have it.

When this happens, the pancreas produces more insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels. to compensate for the body's poor response to existing insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels., and in the early stages, this will be enough to balance things out.

As time passes, though, the pancreas can no longer produce enough insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels. to compensate, leading to a relative insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels. deficiency. This deficiency gradually becomes worse as, in time, beta cellThe basic unit of all living organisms. function is impaired and the cells are reduced in number by around 20 to 30 per cent.[1]

Resistance to insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels. in the liverA large abdominal organ that has many important roles including the production of bile and clotting factors, detoxification, and the metabolism of proteins, carbohydrates and fats. and muscles leads to:

  • Increased production of glucoseA simple sugar that is an important source of energy in the body. in the liverA large abdominal organ that has many important roles including the production of bile and clotting factors, detoxification, and the metabolism of proteins, carbohydrates and fats.
  • Underuse of glucoseA simple sugar that is an important source of energy in the body. in the muscles.

These cause hyperglycaemiaA high level of glucose in the blood. (high levels of glucoseA simple sugar that is an important source of energy in the body. in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid.) in a similar way to type 1 diabetes.[1]

High glucoseA simple sugar that is an important source of energy in the body. levels in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. lead to glucoseA simple sugar that is an important source of energy in the body. appearing in the urine, along with increased urine production and excessive thirst. These symptoms are more subtle in type 2 than in type 1 diabetes, as hyperglycaemiaA high level of glucose in the blood. develops more slowly. Also, weight loss and wasting are rare.

People with type 2 diabetes may feel tired but have no other symptoms at all; because of this, many people with type 2 diabetes do not know they have it.[1]

Often, people with type 2 diabetes also have high bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. pressure, elevated cholesterolA substance present in many tissues and an important constituent of cell membranes although high concentrations of a certain type of cholesterol in the blood are unhealthy. in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. and abdominal (central) obesityExcess accumulation of fat in the body. as well as insulin resistanceA reduced response of the body to the hormone insulin, resulting in raised blood glucose levels.. Together, these features may be called the 'metabolic syndromeThe combination of insulin resistance, abdominal obesity, high blood pressure and disordered blood lipids that increases the risk of cardiovascular disease.', a clustering of risk factors that increases the risk of stroke and heart disease.[1]

A number of factors may contribute to insulin resistanceA reduced response of the body to the hormone insulin, resulting in raised blood glucose levels.:

  • Abdominal obesityExcess accumulation of fat in the body. leads to higher levels of free fatty acidsThe basic building blocks of many lipids., components of fatOne of the three main food constituents (with carbohydrate and protein), and the main form in which energy is stored in the body. tissue, in the bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid..  The fatty acids compete with glucoseA simple sugar that is an important source of energy in the body. for use by the muscleTissue made up of cells that can contract to bring about movement. cells. Furthermore, the fatty acids are processed by the liverA large abdominal organ that has many important roles including the production of bile and clotting factors, detoxification, and the metabolism of proteins, carbohydrates and fats., increasing glucoseA simple sugar that is an important source of energy in the body. production[4]
  • Lack of exercise also plays a role, partly because inactivity can lead to the accumulation of free fatty acidsThe basic building blocks of many lipids. within the muscles[1]
  • Abdominal fatty tissue releases a number of hormones - for example, steroids such as cortisolA steroid hormone important for helping to regulate carbohydrate metabolism and the stress response.. These influence insulinA hormone produced by the beta cells of the pancreas that acts to lower blood glucose levels. sensitivity in other parts of the body, such as the muscles and liverA large abdominal organ that has many important roles including the production of bile and clotting factors, detoxification, and the metabolism of proteins, carbohydrates and fats..[1]

However, although obesityExcess accumulation of fat in the body. increases insulin resistanceA reduced response of the body to the hormone insulin, resulting in raised blood glucose levels., most people who are obese do not develop diabetes.[5] This is because genes also play a part in whether or not you develop diabetes.[3,6]

References: 
  1. Boon NA, Colledge NR and Walker BR. Davidson's Principles and Practice of Medicine Churchill Livingstone Elsevier. 2006; 20th edition.
  2. Translational mini-review series on type 1 diabetes: immune-based therapeutic approaches for type 1 diabetes. Staeva-Vieira T, Peakman M and von Herrath M. Clinical and Experimental Immunology. 2007;148:17-31.
  3. Longmore M, Wilkinson I and Török E. Oxford Handbook of Clinical Medicine 2002; 5th edition.
  4. Islet cellThe basic unit of all living organisms. dysfunction in progression to diabetes mellitusDisordered energy metabolism and high levels of glucose in the blood owing to a lack of insulin, or poor response of the body to insulin.. Spellman CW. J Am Osteopath Assoc. 2007;107(suppl 3):S1-5.
  5. Beta-cellThe basic unit of all living organisms. apoptosisA natural process of programmed cell death, for example, when cells are old or damaged. in the pathogenesis of human type 2 diabetes mellitusDisordered energy metabolism and high levels of glucose in the blood owing to a lack of insulin, or poor response of the body to insulin.. Leonardi O, Mints G and Hussain MA. European Journal of Endocrinology. 2003;149:99-102.
  6. Beta-cellThe basic unit of all living organisms. failure in diabetes and preservation by clinical treatment. Wajchenberg BL. Endocrine Reviews. 2007;28:187-218.