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Written by Ada’s Medical Knowledge Team

Updated on

What is diabetes?

Diabetes mellitus, commonly referred to as diabetes, is a condition in which the body’s blood glucose, or blood sugar, is too high. Glucose comes from the food we eat and is the body’s main source of energy. It is helped to reach the cells of the body by insulin, a hormone produced in the pancreas. Diabetes occurs when the body produces no or insufficient quantities of insulin to do this, and so glucose builds up in the blood. 1

Read more about diabetes in Ada’s dedicated diabetes guide.

Persistently high blood glucose levels can, over time, cause health problems such as heart disease, stroke, kidney failure and vision loss. 2 With proper treatment, however, diabetes can generally be managed effectively and complications minimised. Treatment will usually be required throughout a person’s life as, currently, there exists no cure for diabetes.

Types of diabetes

There are a number of types of diabetes, though type 1 and type 2 are the most common. Of these, type 2 diabetes is by far the most common, accounting for approximately 90 percent of all cases of diabetes in Europe and North America. 3

Type 1 diabetes

Type 1 diabetes typically develops in children and young people, though it can affect people of any age. It occurs when the body ceases to produce insulin and blood glucose levels become very high. This results from the body’s immune system mistakenly attacking the healthy cells in the pancreas responsible for producing insulin. 4

The underlying cause of type 1 diabetes is not fully understood. Although not classed as a hereditary disorder, a person is more likely to develop type 1 diabetes if a close relative, such as a parent or a sibling, has the condition.

The symptoms of type 1 diabetes typically come on quickly, over a number of days or weeks, and include thirstiness, tiredness and a need to urinate frequently. Treatment generally involves the use of insulin injections. 5 With proper management, type 1 diabetes can usually be controlled effectively.

Type 2 diabetes

Type 2 diabetes typically affects people over the age of 40, though it is becoming increasingly common in those of a younger age. This type of diabetes occurs when the body ceases to produce sufficient amounts of insulin, or when the body does not use insulin properly (something known as insulin resistance). It may also be caused by a combination of the two. 6

Type 2 diabetes is often linked to being overweight or obese. The disorder also tends to run in families and is more common in people of Caribbean, African or South Asian descent. Symptoms typically develop slowly, over a number of months or years, and include thirstiness, tiredness and a need to urinate frequently. Treatment typically involves lifestyle changes such as eating a healthy diet and regular exercise, however in some cases medication may also be required to manage blood sugar levels. 6

Read more about Type 2 Diabetes »

Other types of diabetes

Type 1 and type 2 diabetes are by far the most common forms of the disorder. However, other types do also exist and include the following:

Gestational diabetes is diabetes that occurs for the first time during pregnancy. People with gestational diabetes have an increased risk of miscarriage, premature delivery, and the need for a cesarean section, though with proper management these risks can be significantly reduced. 7

Maturity onset diabetes of the young (MODY) is a rare, hereditary form of diabetes caused by a mutation of a single gene. In many cases, the signs and symptoms of MODY are mild and the condition may go unnoticed, only to be identified through routine testing or testing for another condition. 8

Neonatal diabetes is a very rare form of diabetes, typically diagnosed in children under six months of age. The condition is caused by a gene mutation. 9

Type 3 diabetes is a proposed alternative name for Alzheimer’s disease, as, in some cases, Alzheimer’s can be linked to insulin resistance. 10

While technically not a form of diabetes, pre-diabetes, or impaired glucose intolerance, should also be noted. This condition occurs when blood glucose levels are high, but not high enough to qualify as diabetes, despite giving a similar risk of heart disease, stroke and other complications normally associated with diabetes. Pre-diabetes is typically managed through lifestyle changes such as losing weight or switching to a healthier diet. 11

Symptoms of diabetes

The symptoms of type 1 and type 2 diabetes typically include: 12

  • Excessive thirst
  • A need to urinate frequently
  • Excessive hunger
  • Fatigue or tiredness
  • Blurred vision
  • Wounds that are slow to heal
  • Unexplained weight loss
  • Tingling and/or pain in the extremities

The symptoms of type 1 diabetes typically develop quickly, over a number of days or weeks, while the symptoms of type 2 diabetes typically develop more gradually, normally over months or years. The symptoms of type 2 diabetes may be hard to detect at first and may sometimes be confused with normal signs of aging.

Causes of diabetes

Both type 1 and type 2 diabetes are caused by an insufficiency of insulin. However, what causes this insufficiency differs in each case.

Type 1 diabetes is, in most cases, an autoimmune disorder. This means that the immune system, which usually attacks unwanted germs and bacteria, mistakenly attacks healthy cells. In the case of type 1 diabetes, the immune system attacks insulin-producing beta cells in the pancreas. What triggers the immune system to do this is not known, though a popular theory suggests that it may be triggered by a virus.

There is also a genetic element to type 1 diabetes. Although it is not a hereditary disorder, if a first-degree relative – a parent or sibling, for example – has the condition, a person stands a greater chance of developing it themselves. In rare cases, type 1 diabetes can also be caused by severe inflammation of the pancreas or the surgical removal of the pancreas. 4 13

Type 2 diabetes is generally caused by a combination of lifestyle and genetic factors. Lifestyle factors include being overweight or obese; eating a diet high in carbohydrates, sugars and fats; and physical inactivity. The likelihood of developing type 2 diabetes also increases significantly if a first-degree relative has experienced the condition. 3

Diabetes complications

With appropriate treatment, many people with diabetes are able to prevent possible complications of the condition occurring.

However, if treatment is not received, or if it is ineffective, a variety of complications can occur. These complications can be serious and possibly life-threatening.

Complications of diabetes include: 14

Cardiovascular disease: Diabetes increases the risk of various cardiovascular problems including stroke, heart attack and atherosclerosis (narrowing of the arteries).

Nerve damage: Nerve damage can cause pain, tingling and numbness, especially in the extremities. Left untreated, this can lead to a total loss of feeling in the affected limbs.

Kidney damage: Damage to the kidneys can, in extreme cases, cause kidney failure and may lead to the need for dialysis or a kidney transplant. Read about the Signs of Kindey Problems »

Eye damage: Diabetes can, in extreme cases, lead to blindness and other vision problems such as cataracts and glaucoma.

Foot damage: Poor blood flow to the extremities and nerve damage can cause various complications. Wounds, for example, can be slow to heal, and this may be particularly problematic when the feet are affected. Serious infections may result, and, in severe cases, amputation may be required.

Hypoglycemia: Insulin taken to treat diabetes can, in some cases, cause blood sugar levels to fall too low. This is called hypoglycaemia, and initial symptoms may include feeling shaky, dizzy, tired or irritable. Mild hypoglycemia can typically be treated by oneself, whereas severe cases may require medical attention.

People who suspect that they may be experiencing a complication of diabetes should speak to a doctor. In addition, the free Ada app can be used to carry out a symptom assessment.

Diabetes and COVID-19

Having diabetes can put you at risk of severe illness due to COVID-19. It's essential to take the necessary precautions to prevent an infection with the virus and get tested as soon as possible if you think you may have been infected.

Read more about the link between COVID-19 and diabetes here.

Diagnosing diabetes

Diagnosing diabetes will typically involve an evaluation of the symptoms being experienced and a variety of diagnostic tests. These tests may include: 15 16

  • Random blood glucose test: A reading of 200mg/dL or above will generally indicate diabetes.
  • Fasting plasma glucose (FPG) test: A reading of 126mg/dL or above will generally indicate diabetes.
  • HbA1c test: A reading of 6.5 or above will generally indicate diabetes.
  • Oral glucose tolerance test: A reading of 200mg/dL or above will generally indicate diabetes.

Tests to distinguish between type 1 and type 2 diabetes, such as a urine ketone test or glutamic acid decarboxylase (GAD) autoantibodies tests, may also be necessary.

Whichever test is used, it will usually be repeated several times to allow doctors to gain an accurate picture of a person’s blood glucose levels.

People displaying symptoms of diabetes should be tested. Moreover, people over the age of 40 should also consider testing, even if they are displaying no symptoms. This is especially true for people within the at-risk groups for type 2 diabetes – people who are overweight or of African, Caribbean or South Asian descent, for example. 15

Diabetes treatment

There is no cure for diabetes, meaning treatment is aimed at managing blood glucose levels and controlling the symptoms and possible complications of the condition. In the majority of cases, diabetes can be successfully managed.

People with type 1 diabetes will usually require regular insulin treatment in order to keep their insulin levels normal. This will typically involve insulin injections, which will be required around two to four times a day. Although some people may use a syringe, in most cases, what is known as an insulin pen or auto-injector will be used. A full explanation of how to administer the insulin will be given upon diagnosis with the condition. Family members or friends may also be taught how to properly do this. 17

The blood glucose levels of people with type 1 diabetes will also need to be regularly checked. This can be done with a home monitoring kit, and can help to determine daily insulin needs. The levels will also be reviewed by doctors to ensure that the overall treatment plan is working effectively. 17

Lifestyle changes are the main method of treatment for type 2 diabetes. This will typically involve: 4 18

Dietary changes: Eating a healthy, balanced diet is key to controlling type 2 diabetes. A dietician will be able to provide guidelines on what to eat, though generally a diet low in fat and high in fibre, fruits and vegetables is recommended.

Exercising: Thirty minutes of moderate-intensity exercise five times per week is generally advised for people with type 2 diabetes.

Losing weight: If a person with type 2 diabetes is overweight or obese, losing weight can be helpful in reducing blood glucose levels. Dietary changes and exercise can help with this.

In many cases, lifestyle changes alone are enough to reduce blood glucose to the target level, leading to remission. However, some people may also require medication. Medications that may be prescribed include metformin, sulfonylurea medicines, nateglinide and repaglinide. 4

Diabetes prevention

Only type 2 diabetes is preventable. This is because this type of diabetes is commonly caused or exacerbated by unhealthy lifestyle choices.

Adopting a healthy, balanced diet is the most important factor in helping to prevent type 2 diabetes. This should be a diet low in carbohydrates, sugar and fat, and high in fruits, vegetables and grains. 19

Other ways to help prevent type 2 diabetes include: 19

  • Maintaining a healthy weight
  • Exercising regularly
  • Not smoking
  • Minimising alcohol intake