Diabetes mellitus is a group of conditions that cause persistently high blood sugar levels. The most common type is type 2 diabetes, but type 1 diabetes, gestational diabetes, and rarer forms can also affect how the body controls blood sugar.
In this article, you’ll learn about the different types of diabetes, what causes them, their symptoms, and how you and your GP can work together to manage and treat the condition.
Three key takeaways
Diabetes mellitus refers to a group of conditions that cause persistently high blood sugar levels that are hard to control.
Type 2 diabetes mellitus is the most common type, but type 1 diabetes, gestational diabetes, and others can also impact daily life.
Early understanding and management can help reduce long-term complications.
What is diabetes mellitus?
Diabetes mellitus refers to a group of health conditions that affect how your body controls blood sugar, also known as glucose. Most people simply call it “diabetes,” although healthcare professionals may use the full medical term.
Diabetes causes blood sugar levels to remain too high over time, a state known as hyperglycaemia. Blood sugar is essential for energy and helps fuel your body’s cells. However, when levels stay high for long periods, it can damage organs and tissues, including the kidneys, eyes, blood vessels, and heart.
Diabetes is linked to problems with insulin, a hormone that helps move sugar from your bloodstream into your cells so it can be used for energy. If your body does not produce enough insulin, or cannot use it effectively, sugar builds up in the blood instead. Over time, this can lead to serious health complications.
Blood sugar levels naturally rise after eating or drinking and fall during physical activity. This balance is a normal and healthy process. But when blood sugar remains consistently high, it can result in diabetes and increase the risk of long-term health problems.
Types of diabetes mellitus
The main types of diabetes mellitus are type 1, type 2, and gestational diabetes. Other types can develop, but they’re far less common.
Type 1 diabetes mellitus
People with type 1 diabetes have high blood sugar because they can’t make insulin. Their immune systems (usually the first line of defence against disease, infection, and injury) attack the cells that make insulin in the pancreas by mistake. This makes type 1 diabetes an autoimmune disease.
Around 8–10% of people with diabetes in the UK have type 1 diabetes. They willneed to take insulin for the rest of their lives. This is why doctors used to call it insulin-dependent diabetes mellitus, but that term is no longer used because it caused confusion.
Most people are diagnosed in childhood or adolescence, but type 1 diabetes can develop at any age. Having type 1 diabetes is more likely if your mum, dad, or siblings have it.
Type 2 diabetes mellitus
Type 2 diabetes mellitus happens when your blood sugar levels become too high because your body does not make enough insulin, or your cells do not respond to insulin properly. As a result, glucose builds up in the bloodstream instead of being used for energy. Over time, this leads to persistently high blood sugar levels.
Around 9 in 10 of the 5.8 million people living with diabetes in the UK have type 2 diabetes. It is also estimated that around 1.3 million people may have the condition without knowing it.
Type 2 diabetes is more common because it is linked to factors such as excess weight, diet, physical activity, age, and family history.
Gestational diabetes
Gestational diabetes can develop during pregnancy in women who do not already have diabetes. It is usually diagnosed between 24 and 28 weeks of pregnancy. Unlike other types of diabetes, gestational diabetes is temporary, and blood sugar levels often return to normal after giving birth.
It can usually be managed through healthy eating and regular, gentle physical activity. Your pregnancy care team will support you and help you understand what is safe for both you and your baby.
However, having gestational diabetes does increase your risk of developing type 2 diabetes later in life. Research from the University of Cambridge suggests that around 1 in 3 women who have had gestational diabetes will go on to develop type 2 diabetes within 15 years if no preventive steps are taken.
Other forms of diabetes mellitus
Other types of diabetes do exist, but they are rare. Around 2 in every 100 people with diabetes have a type that is not type 1 or type 2.
Some rarer forms of diabetes are genetic, meaning they are passed from parents to children. These include:
Alström syndrome, a rare inherited condition that can affect insulin production and blood sugar control
Maturity onset diabetes of the young (MODY)
Neonatal diabetes, which is diagnosed in babies under 6 months old
Wolfram syndrome, also known as DIDMOAD syndrome, a rare genetic disorder
Latent autoimmune diabetes in adults (LADA), sometimes called type 1.5 diabetes, can also develop. It shares features of both type 1 and type 2 diabetes and usually appears later in adulthood.
Diabetes can also develop as a result of other health conditions, particularly those that damage the pancreas. The pancreas produces insulin, so damage to this organ can affect how much insulin your body makes. Conditions linked to this type of diabetes include:
Acute pancreatitis
Chronic pancreatitis
Pancreatic cancer
Cystic fibrosis
Haemochromatosis
Some medicines can also raise blood sugar levels. For example, steroids prescribed for other health conditions may increase blood sugar and, in some cases, lead to diabetes.
Type 1 diabetes vs type 2 diabetes mellitus
Type 1 and type 2 diabetes affect people in different ways, develop for different reasons, and are treated differently.
People with type 1 diabetes cannot produce insulin at all. In type 2 diabetes, the body either does not make enough insulin or cannot use it effectively. Symptoms of type 1 diabetes usually appear quickly and can be severe. By contrast, type 2 diabetes often develops slowly, with symptoms that may take years to appear and are easy to miss.
There is currently no cure for type 1 diabetes, and doctors do not fully understand why it develops, although certain genes are known to increase risk. For type 2 diabetes, a number of risk factors are well established, including age, family history, ethnicity, waist size, and having overweight or obesity.
Because of this, there is no known way to prevent type 1 diabetes. However, evidence shows that many cases of type 2 diabetes can be delayed or prevented through lifestyle changes.
Treatment also differs between the two types. Healthy eating, regular physical activity, and routine health checks are important for everyone with diabetes. People with type 1 diabetes need insulin and careful monitoring of carbohydrate intake. Some people with type 2 diabetes will also need medication or insulin, while others can manage their condition without medication.
Type 1 Diabetes
Type 2 Diabetes
Making insulin
The body cannot make any insulin.
The body doesn't make enough or insulin doesn't work well.
Symptom onset
Symptoms appear very quickly.
Early symptoms are often easy to miss and develop slowly.
Causes
Autoimmune destruction of insulin‑producing cells. The cause of this is unknown, but specific genes may increase risk.
Insulin resistance and progressive insulin deficiency influenced by diet, age, family history, ethnicity, waist circumference, and body weight
Prevention
No known way to prevent or cure it.
Steps can be taken to prevent it or bring blood sugar down to healthy levels.
Healthy eating, exercise, and regular GP check-ins.
What causes diabetes mellitus?
The cause of diabetes mellitus depends on the type. The high blood sugar levels linked to every type of diabetes happen because of problems with either making or using insulin. Known causes or risk factors of some types might include:
Genetics
Ethnicity
Other health conditions
Taking certain medications, like steroids
Pregnancy
For some types of diabetes, such as type 1, the exact cause is not fully understood. Diet, body weight, and physical activity do not influence whether someone develops type 1 diabetes. However, lifestyle factors such as diet, weight, and activity levels can increase the risk of developing other types, including type 2 diabetes.
Causes of type 2 diabetes mellitus
Type 2 diabetes develops when insulin does not work effectively. This can happen because the body does not produce enough insulin, or because cells do not respond properly to it, meaning glucose stays in the bloodstream. This reduced response to insulin is known as insulin resistance. Over time, the pancreas may no longer be able to produce enough insulin to overcome this resistance.
Age and family history can increase the likelihood of developing type 2 diabetes. People from African-Caribbean, Black African, Chinese, and South Asian backgrounds are also at higher risk.
You cannot change these risk factors. However, factors such as body weight, diet, and physical activity can also affect risk, and these are within your control. Making changes in these areas can help improve blood sugar control and reduce the risk of developing type 2 diabetes.
Is diabetes mellitus genetic?
Parents can pass on a higher risk of developing certain types of diabetes, including the two most common forms, type 1 and type 2. However, having a family history does not mean you will definitely develop diabetes. For example, you are around 2 to 6 times more likely to develop type 2 diabetes if a close family member, such as a parent or sibling, has it.
Type 1 and type 2 diabetes are thought to develop due to a combination of genetic and environmental factors. For type 1 diabetes, many of the triggers are still unknown. In type 2 diabetes, risk is influenced by factors such as family history and ethnicity, alongside lifestyle factors like diet and physical activity.
Some very rare forms of diabetes, such as Alström syndrome or Wolfram syndrome, are inherited directly from one generation to the next.
Diabetes mellitus and complications
Without treatment, diabetes mellitus can harm other organs and cause serious health issues over time. This can damage the kidneys, eyes, heart, nerves, feet, teeth, gums, and lungs, as well as increase your risk of stroke. But staying on top of diet, lifestyle, and medications can prevent these complications.
Diabetes mellitus and kidney disease
Diabetes is an extremely common cause of kidney disease. In fact, one in three people with diabetes develop kidney disease, and diabetes is the second most common cause of kidney failure in the UK, according to Kidney Research UK.
The kidneys’ job involves filtering harmful stuff from your blood. They do this with tiny, delicate filters called glomeruli. Constantly high blood sugar damages these filters. Eventually, the damage can be severe enough to mean you need a kidney transplant or a process called dialysis to keep your blood clean.
Plus, if you’re older and have type 2 diabetes, high blood pressure, blood vessel issues, or heart disease might already have damaged the kidneys. This may mean kidney problems occur even quicker.
Doctors will test for kidney disease as part of your check-ins for diabetes treatment. Keeping on top of blood sugar control can protect your kidneys’ long-term ability to filter your blood.
Ketoacidosis in diabetes mellitus
Diabetic ketoacidosis (DKA) is another life-threatening diabetes mellitus complication, mainly in those with type 1 diabetes. If you don’t make any insulin, a waste product called ketones can build up in your blood and make it acidic.
You can test for ketones at home. If you have type 1 diabetes or manage type 2 diabetes with insulin and feel any of the following symptoms, use either a meter or strips to test your wee for ketones:
Breath that smells like fruit, similar to nail polish remover, or like pear drops
Extreme tiredness or confusion
Blurry vision
Having a meter reading of over 3 millimoles per litre (mmol/L) or a strip reading of over 2+, head to your nearest accident and emergency. DKA is a medical emergency. Even if your ketones are slightly high (0.6-1.5 mmol/L) and you feel a little unwell, or quite high (1.6-3 mmol/L) and you feel fine, call your GP or 111.
DKA is treatable in a hospital with a drip that feeds you fluids, nutrients, and insulin.
Diabetes mellitus treatments and medications
Your diabetes mellitus treatment will depend on the type of diabetes you have. While there is no cure, diabetes can be effectively managed to control blood sugar levels and reduce the risk of complications.
Regular check-ins with a doctor are important for all types of diabetes, alongside paying attention to diet and physical activity. If you have type 1 diabetes, you will need insulin therapy for life, given either by injection or through an insulin pump to replace the insulin your body no longer makes.
People with type 2 diabetes may need medication to help control blood sugar, taken either by mouth or as injections. Many people with type 2 diabetes can manage their condition through healthy eating and regular physical activity alone, and most will not need insulin.
People with type 1 diabetes also need to balance food and physical activity. Insulin doses must be adjusted to match what you eat and how active you are, which helps keep blood sugar levels within a safe range.
A GP, diabetes educator, dietitian, and other healthcare professionals can work with you. Together, they can create a diabetes management plan that fits your lifestyle and needs.
What is the treatment for type 2 diabetes mellitus?
Type 2 diabetes is treated using a step-by-step approach that focuses on controlling blood sugar, reducing health risks, and supporting long-term wellbeing. Treatment is tailored to you and adjusted over time based on how well your blood sugar is controlled and whether you have other health conditions, such as heart or kidney disease.
Doctors usually follow a structured treatment pathway. Each step builds on the last, rather than replacing it. For example, adding medication does not mean stopping healthy eating or physical activity.
First-line treatment
Healthy eating, regular physical activity, and metformin are usually the starting point for type 2 diabetes treatment. If someone already has heart failure or cardiovascular disease, doctors may also prescribe SGLT2 inhibitors at this stage.
Dual therapy
If blood sugar targets are not met, a second medication is added. This may be an oral or injectable treatment, such as:
Sulfonylureas
DPP-4 inhibitors
SGLT2 inhibitors (if not already added)
GLP-1 receptor agonists
Triple therapy
If further control is needed, a third medication may be introduced. This can include injectable treatments such as insulin. If triple therapy is ineffective, not tolerated, or contraindicated, your specialist may consider switching one of the treatments for a GLP-1 receptor agonist for certain patient groups.
Many type 2 diabetes medicines work by lowering blood sugar throughout the day or after meals. Some treatments, such as GLP-1 receptor agonists, can also support weight loss in people with type 2 diabetes and obesity. Doctors may also prescribe medications that help protect kidney health and reduce the risk of diabetes-related complications.
Most importantly, treatment is personalised. Your doctor will work with you to create a plan that fits your body, lifestyle, and health goals, and will support you to stick with it over time.
Diabetes mellitus diets and lifestyle management
Diet and lifestyle changes are a core part of managing diabetes mellitus. Different foods affect blood sugar at different speeds, so adjusting what you eat and how active you are can help keep blood sugar levels within a healthy range.
Diet and blood sugar control
Foods high in sugar and refined carbohydrates, such as sweets, chocolate, white bread, and pasta, can cause rapid blood sugar spikes. Reducing these foods and choosing more balanced meals can help improve blood sugar control.
Eating well also supports weight management. Around 9 in 10 adults newly diagnosed with type 2 diabetes have obesity, and losing a significant amount of weight can reduce the risk of complications and, in some cases, lead to type 2 diabetes going into remission.
You can learn more about which foods and drinks to limit and which to include on our diabetes diet page.
Weight management support
Weight management can play a major role in improving blood sugar control. Your GP can discuss support options with you, including referrals to a dietitian for personalised meal planning. For some people with type 2 diabetes, weight loss medications may also be available through the NHS.
Physical activity and diabetes
Regular physical activity helps your body use blood sugar for energy, making it easier to keep levels under control. Exercise does not need to mean structured workouts or running. Starting small and building activity into daily life can be just as effective.
Simple changes like walking part of your commute, dancing at home, or doing gardening or housework all count. If you use insulin or other blood-sugar-lowering medications, check your blood sugar before and after activity to help prevent low blood sugar episodes.
“Making lifestyle changes when you have diabetes mellitus isn't just about managing blood sugar - it's about taking charge of your overall health and wellbeing. When you combine healthier eating with more movement, they work together like a team.
Exercise helps your body use the food you eat more effectively, whilst a balanced diet gives you the energy to stay active. These changes can also help protect your heart, improve your mood, and boost your energy levels throughout the day.
What's really encouraging is that for many people with type 2 diabetes, sticking with these lifestyle changes can mean needing fewer medications over time, or lower doses. Your body responds really well to the care you give it!”
Ian Budd, Prescribing Pharmacist
Can diabetes mellitus be prevented?
Some types of diabetes, particularly type 2, can be prevented or delayed. In fact, around half of all diabetes diagnoses could be prevented or pushed back with early action. Small, everyday changes to diet and physical activity can make a meaningful difference over time.
Getting the right support is one of the most effective ways to reduce your risk. This might include joining a weight loss programme, speaking with a dietitian or exercise specialist, or taking part in a type 2 diabetes prevention programme.
Acting early can help you take control of your health. If you begin to notice symptoms of diabetes or are found to have high blood sugar during a health check, making changes sooner can lower your risk and help prevent diabetes-related complications.
How to prevent type 2 diabetes mellitus
Type 2 diabetes can often be prevented or delayed by improving diet, increasing physical activity, managing weight, and having regular health checks. Small, realistic changes made consistently can significantly reduce your risk.
Eat a balanced, diabetes-friendly diet
Choosing foods that support steady blood sugar levels can help lower your risk. Eating more of the following may reduce diabetes risk for some people:
Fruit and vegetables
Whole grains
Cheese and yoghurt
Unsweetened coffee and tea
It can also help to eat less of foods linked to a higher diabetes risk, including:
Sugary drinks
Processed red meats, such as sausages, ham, and bacon
Refined carbohydrates, like white bread, sugary cereals, and sweets
Potatoes, especially chips
Be physically active in ways you enjoy
Regular movement helps your body use blood sugar for energy. This does not have to mean intense exercise. Walking, cycling, gardening, dancing, or taking the stairs all count. Finding activities you enjoy makes them easier to stick with long term.
Aim for gradual, sustainable weight loss
Losing as little as 5% of your body weight can reduce your risk of type 2 diabetes, particularly if you have raised blood sugar levels. You do not need to change everything at once. Small daily habits can add up over time.
Get regular health checks
Many people do not realise they are at risk of type 2 diabetes. Regular health checks are the best way to monitor blood sugar levels and spot problems early.
If you are between 40 and 75 years old and do not already have diabetes or cardiovascular disease, you are eligible for a free NHS Health Check. Contact your GP surgery to arrange one and learn more about your diabetes risk.
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