Understanding diabetes: types, causes, symptoms and treatments

Almost five million people in the UK live with diabetes, a condition that was discovered over 2,250 years ago by an ancient Greek physician called Aretaeus of Cappadocia. Diabetes literally translates as ‘syphon’ in ancient Greek — a name Aretaeus thought appropriate when he noticed people with the condition were passing lots of urine, a symptom that remains a key indicator for diabetes today. 

There are several different types of diabetes but all of them are long-term conditions with significant implications for your health. Here we’ll explore the types, causes, symptoms and treatments for diabetes.

Types of diabetes

The two main types of diabetes are diabetes mellitus and diabetes insipidus. The vast majority of diabetes cases in the UK and worldwide are diabetes mellitus. Mellitus means ‘sweet’ in Latin and refers to the high levels of a sugar called glucose that is found in the blood and urine of individuals with uncontrolled diabetes mellitus. Diabetes insipidus is a very rare form of diabetes, which is completely unrelated to diabetes mellitus and is most often caused by the lack of a hormone in the brain called vasopressin.

Diabetes mellitus can be further split into different types; type 1 and type 2 diabetes.

Type 1 diabetes

Type 1 diabetes is an autoimmune disease, which means your body’s own immune system mistakenly attacks and destroys your healthy cells. In type 1 diabetes, beta-cells in your pancreas are destroyed — these cells produce the hormone insulin. In a healthy body, insulin is released to tell your cells to absorb glucose from your bloodstream. This doesn’t occur in people with type 1 diabetes and consequently, from the moment they are diagnosed, they need treatment with insulin. 

Type 1 diabetes is most often diagnosed in young people under the age of 40, who are a healthy weight. There is usually no history of type 1 diabetes in the family but often there is a family or personal history of other autoimmune conditions, such as those affecting the adrenal glands (eg Addison’s disease), the skin (eg vitiligo) or the gut (eg coeliac disease, vitamin B12 deficiency causing pernicious anaemia). Type 1 diabetes only accounts for around 10% of all cases of diabetes, making type 2 diabetes the most common type of diabetes. 

Type 2 diabetes

Type 2 diabetes occurs when your pancreas can’t make enough insulin to deal with the amount of glucose in your blood and/or your cells have become less responsive to insulin. 

It most often occurs in individuals who are overweight or obese. You can determine whether you are overweight or obese by calculating your body mass index (BMI) ie your weight in kilograms divided by your height in metres squared. For individuals of Caucasian descent, a healthy BMI is generally considered between 18 to 25. For individuals of Asian, Afro-Caribbean or African descent, a healthy BMI is generally considered between 18 to 23. A BMI above these ranges means you are overweight, with a BMI of 30 or more meaning you are obese. 

Other risk factors for type 2 diabetes include long-term use of steroids (eg prednisolone, hydrocortisone or dexamethasone) and a family history of the disease. Unlike type 1 diabetes, it is not associated with a family or personal history of other autoimmune conditions. 

For women, another risk factor is gestational diabetes — diabetes that develops for the first time in pregnancy due to changes in hormones that make cells less responsive to insulin during pregnancy. Although after birth gestational diabetes goes away, these women are still at greater risk of developing type 2 diabetes in later life and therefore need an annual blood test to check for this. 

Symptoms of diabetes

Type 1 and type 2 diabetes share the same symptoms. Diabetes UK defined them as the four Ts: 

  • Thinner — unintentionally losing weight or looking thinner than usual
  • Thirsty — often feeling thirsty and not being able to quench your thirst despite drinking
  • Tired — feeling more tired than usual
  • Toilet — needing to urinate very often; in children, bedwetting after they have already learned to control their urination, or in babies, very heavy nappies

As type 2 diabetes often occurs in older individuals, some of these symptoms, such as tiredness and urinating more often, are easily dismissed as part of getting older, while weight loss doesn’t occur in everyone with undiagnosed diabetes. It is, therefore, important to see your doctor if you’re concerned about any of these symptoms. 

Why do these symptoms occur?

When you eat a meal, glucose from your food is dissolved in your blood and in your urine. From an evolutionary standpoint, your body sees glucose as a very precious commodity, which is why your kidneys are so efficient at absorbing as much glucose as possible from your urine.

However, when there is too much glucose in your blood and subsequently in your urine, your kidneys become overwhelmed and can’t absorb all the glucose in your urine. This result is ‘sweet urine’ — in ancient Greek times the only way to test whether someone had diabetes was to taste their urine to check if it was sweet.

‘Sweet urine’ causes the bacteria that live in your genitals and urinary system to overgrow as they feed on the abundance of glucose. This causes the yeast infection, thrush. Weight loss is similarly caused by passing out urine high in glucose. Glucose is a form of energy, so losing glucose in your urine means you are losing calories. This will also make you tired as your cells fail to get the energy they need from the glucose passing through your body.

Finally, thirst can also be explained by the large amounts of glucose in your body. Your body can’t get rid of this glucose unless it’s dissolved in fluid and so it pulls as much water as it can out of your body to dissolve the glucose. This results in you urinating more and becoming dehydrated.

Why treating diabetes is essential

In the case of type 1 diabetes, where no insulin is produced, without treatment with insulin, individuals develop diabetic ketoacidosis (DKA). This is a life-threatening condition and needs prompt emergency medical treatment to prevent death. 

In the case of type 2 diabetes, a lack of treatment doesn’t result in DKA but your blood glucose levels can become dangerously high. Before eating, a healthy blood glucose level should be in the range of 3.5–6 mmol/l. In those with undiagnosed type 2 diabetes who then take medications that can further raise their blood glucose levels (eg steroids), levels can rise to 80–120 mmol/l. This severe hyperglycaemia can be life-threatening.

Undiagnosed or poorly managed diabetes can also have long-term consequences due the effects of the disease on your blood vessels. Damage to small blood vessels (microvascular disease) affects your eyes (retinopathy), kidneys (nephropathy) and nerves (neuropathy). Damage to large blood vessels affects your heart and brain, increasing your risk of heart attacks and stroke

Diabetes is a leading cause of sight loss, the most common cause of end-stage kidney disease and the most common cause of foot amputations, which is caused by diabetic nerve damage.

The steps taken to control and treat your diabetes in the first 10 years after your diagnosis can significantly decrease your risk of these diseases and therefore affect the quality of the rest of your life. As soon as you are diagnosed, it is, therefore, important to get treatment and keep up with your follow-up appointments to monitor your condition. 

Monitoring your diabetes

On a day-to-day basis, you can measure your blood glucose levels with a simple pin prick blood test. However, your care team will also take a long-term view to monitoring your diabetes. Once you are diagnosed, you will need to have a special blood test every few months called the HbA1c test. This measures your average blood glucose levels for the past two to three months by detecting levels of glycated haemoglobin ie glucose that has stuck to your red blood cells. Your red blood cells are renewed every two to three months, which is why this blood test is usually only performed quarterly. 

If your diabetes is well-controlled, your HbA1c result should be between 45–55 mmol/mol and never higher than 60 mmol/mol. Studies show that when these levels are maintained for the first 10 years after diagnosis, the risk of developing disease due to damage to your small or large blood vessels is significantly reduced for the rest of your lifetime. 

In addition to blood tests to monitor your diabetes, you will also need to have annual diabetic eye screenings, urine tests and examinations of your feet to check for nerve damage — your feet are usually the first part of your body to show diabetic nerve damage. 

Early detection of diseases caused by diabetes means you can get appropriate treatment. In the case of diabetic eye and kidney diseases, damage can be stopped and often reversed. However, without regular monitoring, damage becomes irreversible and all that can be done is to slow down the damaging effects. 

How to reduce your risk of diabetes

You can’t prevent type 1 diabetes. However, there are several steps you can take to reduce your risk of developing type 2 diabetes. Specifically, maintain a healthy weight, follow a healthy, balanced diet and exercise regularly. Exercise doesn’t have to mean going to the gym or playing a sport; it can be as simple as getting off the bus a stop earlier to increase the distance you walk or taking the stairs instead of the lift. Incorporating regular physical activity into your daily routine is often a more achievable and maintainable way to stay fit. 

Somebody walking up a staircase

Dispelling diabetes myths

There is a commonly held myth that if you develop diabetes it is “all your fault”. This is completely untrue for type 1 diabetes and even with type 2 diabetes, there is a strong genetic component, which you have no control over. So although there are clear steps you can take to reduce your risk of developing type 2 diabetes, there shouldn’t be any guilt associated with getting a diagnosis.

In terms of the genetic contribution to type 2 diabetes, there is a well-established theory called the thrifty genotype hypothesis or the Barker hypothesis, which was proposed by the British epidemiologist David Barker. It suggests that if a mother became pregnant during a time when there was a lack of nutritious food available (eg during WW2 and post-war rationing), the way her baby’s genes work would have changed to prepare the baby to be born into an environment where food is scarce.

The baby becomes better at efficiently storing energy as fat. However, if the baby subsequently doesn’t live through a time of food scarcity and has easy access to ample amounts of food, the changes in the way their genes work will now put them at an increased risk of obesity. Not only that, it is thought that these changes can be passed down to the next generation. It is, therefore, possible that many individuals today are carrying these genetic changes, which makes them more likely to become overweight, a major risk factor for developing type 2 diabetes.

Current and future diabetes treatments

Currently, the main treatment for type 1 diabetes is insulin, while for type 2 diabetes there’s a wide range of medications that can be prescribed to control your blood glucose levels and in some cases, also help you lose weight. 

Researchers continue to develop innovative new treatments for diabetes. One in particular that could have a big impact on diabetes management is a new drug to be launched near the end of 2023. Given once a week as an injection, it not only offers excellent control of blood glucose levels but also results in considerable weight loss, almost equivalent to weight loss achieved through weight loss surgery

As treatments advance, it will nonetheless continue to be vital that diabetes is diagnosed and treated early. So if you are concerned that you have diabetes, see your GP as soon as possible. 

Author biography

Professor Ketan Dhatariya is a Consultant in Diabetes and Endocrinology & General Medicine at Spire Norwich Hospital and is the world's leading specialist in diabetic ketoacidosis (DKA) according to Expertscape. He also specialises in perioperative diabetes care, the management of diabetes-related emergencies and the ‘diabetic foot’. In addition to his clinical expertise, Professor Dhatariya holds a PhD in Inpatient Diabetes from the University of East Anglia (UEA) and is an Honorary Professor of Medicine at the UEA. He is an active member of the research community and has published over 160 peer-reviewed papers.