Condition

Diabetes

Diabetes is a metabolic disorder characterised by a persistently elevated blood glucose level. It arises from problems with insulin secretion (insulin deficiency), insulin action (insulin resistance) or a combination of the two.

First published: 21 Mar 2025

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Definition

Diabetes is associated with the development of macrovascular problems (eg myocardial infarction, stroke and peripheral vascular disease) and microvascular problems (eg retinopathy, nephropathy and neuropathy). Other complications associated with diabetes include:

periodontitis
gastroparesis
fatty liver disease
erectile dysfunction
depression
dementia (National Institute for Health and Care Excellence, 2024a; 2024b)

An estimated 5.6 million people in the UK have diabetes, and this prevalence is increasing (Diabetes UK, 2025). Overall, 4.4 million people have a formal diagnosis of diabetes, with an additional 1.2 million thought to be undiagnosed (Diabetes UK, 2025). A further 6.4 million people are at high risk of diabetes, based on blood glucose readings indicating prediabetes or non-diabetic hyperglycaemia (Diabetes UK, 2025).

Type 2 diabetes is the most common form of diabetes, accounting for around 90% of cases in the UK (Diabetes UK, 2025). Type 1 diabetes represents approximately 8% of cases in the UK (Diabetes UK, 2025).

Classifications of diabetes include:

type 1 diabetes
latent autoimmune disease in adults (LADA)
type 2 diabetes
monogenic diabetes (eg maturity-onset diabetes of the young (MODY))
pancreatogenic diabetes
gestational diabetes
other endocrine disorders (eg Cushing’s syndrome,
hyperthyroidism)
drug-induced diabetes (eg corticosteroids, anti-psychotics) (American Diabetes Association, 2024; World Health Organization, 2025)

Symptoms

Presenting symptoms of diabetes include:

polyuria (excessive urination)
polydipsia (excessive thirst)
polyphagia (feeling of extreme, insatiable hunger)
weight loss
fatigue
blurred vison
recurrent infections

Symptoms tend to evolve gradually in type 2 diabetes, whereas they are typically more apparent in type 1 diabetes, often with additional symptoms and signs that reflect the onset of diabetic ketoacidosis, including:

vomiting
abdominal pain
confusion
fruity breath smell
deep laboured breaths (Kussmaul respiration) with signs of dehydration and shock (National Institute for Health and Care Excellence, 2024a; 2024b)

Symptoms of MODY are often mild, so diagnosis may be a chance finding from routine testing (Urakami, 2019).

If pancreatogenic diabetes is suspected, it is important to ask about gastrointestinal symptoms, as pancreatic exocrine function may also be affected. Gastrointestinal symptoms can include:

upper abdominal pain
steatorrhoea (too much fat in the stool)
bloating
weight loss (Morris and Moulik, 2024)

Pancreatic enzyme insufficiency usually predates diabetes onset (Morris and Moulik, 2024).

Aetiology

Type 1 diabetes

Type 1 diabetes is an autoimmune disorder, where antibodies are directed against the insulin-producing pancreatic beta-cells that lead to insulin deficiency, often arising in children and young people. Risk factors for type 1 diabetes include a family history of the condition or a personal or family history of other related autoimmune conditions, for example:

thyroid disorders
pernicious anaemia
coeliac disease
vitiligo
Addison’s disease (National Institute for Health and Care Excellence, 2024b)

Type 2 diabetes

Insulin resistance is the hallmark of type 2 diabetes, and is linked to central adiposity (collection of fat around abdominal area). Insulin levels may increase initially in an attempt to overcome insulin resistance, but when this compensatory mechanism fails, hyperglycaemia (where blood sugar levels are too high) ensues. Pancreatic beta cell function declines over time and ultimately exogenous insulin may be required to optimise glucose levels.

Risk factors for type 2 diabetes include:

overweight or obesity (critical factor is central adiposity)
family history of type 2 diabetes
Asian, African, Afro-Caribbean or Chinese ethnicity
gestational diabetes
polycystic ovarian syndrome
low-fibre, high-glycaemic index diet
certain drugs (eg corticosteroids, antipsychotics) (National Institute for Health and Care Excellence, 2024a)

The incidence of type 2 diabetes increases with age, but with rising levels of obesity in children and young people, the condition is becoming increasingly diagnosed in younger age groups. Waist circumference is a more accurate measure of central adiposity than body mass index; the National Institute for Health and Care Excellence (2025) recommends measuring waist-to-height ratio in people with a body mass index <35 kg/m2.

Maturity-onset diabetes of the young

Individuals with MODY possess a single gene defect that affects beta cell insulin production. There is a 50% chance of passing on the genetic mutation from parent to child (autosomal dominant inheritance) (Urakami, 2019).

Pancreatogenic diabetes

Possible causes of pancreatogenic diabetes (type 3c diabetes) include:

pancreatitis
pancreatectomy
trauma
pancreatic carcinoma
cystic fibrosis
haemochromatosis (Morris and Moulik, 2024)

Alcohol, smoking and pancreatic duct obstruction are important risk factors for pancreatitis.

Diagnosis

Type 1 diabetes

Characteristic diagnostic features of type 1 diabetes include rapid weight loss and osmotic symptoms of diabetes, often with clinical features of diabetic ketoacidosis with a random plasma glucose level >11.0 mmol/L. Ketone testing is essential if type 1 diabetes is suspected or for those with type 1 diabetes who have high glucose levels, acute illness and as part of ‘sick day advice rules’ where diabetic ketoacidosis is a possibility (National Institute for Health and Care Excellence, 2022a).

C-peptide levels (a measure of insulin reserve) and pancreatic autoantibody testing can help determine the type of diabetes. C-peptide levels will be low in type 1 diabetes.

Type 2 diabetes

Type 2 diabetes is suspected on the finding of hyperglycaemia that may be accompanied by the clinical features (see ‘Symptoms’ above). Diagnosis can be made by:

glycated haemoglobin (HbA1c) ≥48 mmol/mol
fasting plasma glucose ≥7.0 mmol/L
random plasma glucose ≥11.1 mmol/L with symptoms or signs of diabetes (National Institute for Health and Care Excellence, 2024a)

If a person is symptomatic, a single HbA1c or fasting plasma glucose test is sufficient to make the diagnosis. If the person is asymptomatic, then testing should be repeated within 2 weeks, preferably using the same test (National Institute for Health and Care Excellence, 2024a).

Maturity-onset diabetes of the young

It is challenging to distinguish MODY from type 1 or type 2 diabetes. Genetic testing is required to prove the diagnosis. The diagnostic criteria for MODY are:

diabetes in two consecutive generations
absence of beta cell autoantibodies
sustained endogenous insulin secretion
onset before 25 years of age in one family member (Hattersley et al, 2018)

Pancreatogenic diabetes

Pancreatogenic diabetes is frequently misclassified, often as type 2 diabetes. Proposed diagnostic criteria for pancreatogenic diabetes are:

pancreatic exocrine insufficiency (faecal elastase-1 testing)
pathological pancreatic imaging (endoscopic ultrasound,
computed tomography or magnetic resonance imaging scan)
absence of type 1 diabetes-associated antibodies (Ewald and Hardt, 2013)

Management

If type 1 diabetes is suspected, immediate (same-day) referral to the diabetes specialist team must be arranged (National Institute for Health and Care Excellence, 2024b).

An individualised approach to managing diabetes is advised (National Institute for Health and Care Excellence, 2022a; American Diabetes Association, 2024). An evidence-based, structured education programme that is appropriate to the individual’s circumstances should be offered at the point of diagnosis. Longer-term goals of managing diabetes are to reduce complications and improve quality of life.

Lifestyle change

Lifestyle change is fundamental to the management of type 2 diabetes. Goals should be achievable and sustainable in the context of the person’s circumstancess.

The National Institute for Health and Care Excellence (2022a) and Diabetes UK (Dyson et al, 2018) offer similar dietary advice for people with type 2 diabetes:

eat more wholegrains, fruit, vegetables, fish, nuts and legumes (high-fibre, low-glycaemic index sources of carbohydrates)
eat less red and processed meat, refined carbohydrates and sugar
sweetened drinks
have two portions of oily fish per week
reduce salt intake
eat low-fat dairy products
replace saturated fats with unsaturated fats and limit intake of trans fatty acids
limit alcohol to <14 units/week

Intensive weight management and lifestyle support for people with type 2 diabetes can achieve high rates of diabetes remission, defined as an HbA1c level of <48 mmol/mol (< 6.5%), measured at least 3 months after discontinuation of all glucose-lowering medication (Lean et al, 2018; 2019).

Dietary advice in type 1 diabetes centres on understanding the glycaemic effect of different foods and drinks, and carbohydrate counting should be offered as part of the education programme (National Institute for Health and Care Excellence, 2022a). For all forms of diabetes, the importance of a healthy diet to reduce cardiovascular risk should be emphasised.

Physical activity is a useful adjunct to dietary change and can improve glycaemic levels, cardiovascular morbidity and mortality, and depression in people with type 2 diabetes (National Institute for Health and Care Excellence, 2022b). The National Institute for Health and Care Excellence (2022b) recommends at least 150 minutes of moderate to vigorous physical activity per week, spread over at least 3 days. In type 1 diabetes, the importance of exercise in reducing cardiovascular risk should be explained, along with the need for careful glucose monitoring and adjustment of insulin doses (National Institute for Health and Care Excellence, 2022a).

HbA1c targets for glycaemic management

HbA1c targets should be individualised and may need to be relaxed to take account of comorbidities, duration of diabetes, life expectancy and frailty. Risk of hypoglycaemia must be considered, with special consideration for people taking insulin or oral medications that induce hypoglycaemia (where blood sugar levels are too low), people with hypoglycaemic unawareness and those who drive or operate machinery (National Institute for Health and Care Excellence, 2022a; 2022b).

Monitoring glucose levels

Self-monitoring of blood glucose or continuous glucose monitoring should be offered to all people who are taking insulin. Consideration should also be given to self-monitoring of blood glucose for people taking oral medication that can induce hypoglycaemia, such as sulfonylureas sulphonylureas (National Institute for Health and Care Excellence, 2022b).

Monitoring should be intensified during pregnancy or for those planning a pregnancy, if episodes of hypoglycaemia are being experienced and during acute illness (National Institute for Health and Care Excellence, 2022a).

All adults with type 1 diabetes should be offered a choice of real-time glucose monitoring or intermittently scanned continuous glucose monitoring, commonly referred to as flash glucose monitoring, which measures interstitial glucose levels (National Institute for Health and Care Excellence, 2022a). All sensors can now provide real-time glucose monitoring if used with a smart phone. Continuous glucose monitoring offers improved glycaemic values and time in a range of glucose readings, with reduced hypoglycaemic burden. Alerts can be set for both hypoglycaemia and hyperglycaemia (Subramanian et al, 2024).

Intermittently scanned continuous glucose monitoring is an option for people with type 2 diabetes on multiple daily insulin injections if they meet one of the below criteria:

experience recurrent or severe hypoglycaemia
have impaired hypoglycaemic awareness
have a condition that prevents them from using self-monitoring of
blood glucose, but flash monitoring is feasible (including people with learning disability or cognitive impairment)
are using self-monitoring of blood glucose eight or more times a day (National Institute for Health and Care Excellence, 2022b)

Pharmacological intervention for glycaemic management

Type 2 diabetes

Pharmacological treatment for type 2 diabetes is outlined below:

First-line treatment: metformin
Second-line treatment: sulfonylureas, dipeptidyl peptidase-4 inhibitors, pioglitazone or sodium-glucose cotransporter 2 inhibitors, depending on individual requirements (first-line if metformin is not tolerated or contraindicated)
Triple oral therapy if necessary
Offer sodium-glucose cotransporter 2 inhibitors as initial dual therapy with metformin for people with atherosclerotic heart disease and those at high cardiovascular risk (assessed using QRISK3), or add to existing therapy if these situations arise subsequently

Sodium-glucose cotransporter 2 inhibitors with evidence of benefit should be used in cases of heart failure with or without reduced ejection fraction. For chronic kidney disease in the context of diabetes, appropriately licensed sodium-glucose cotransporter 2 inhibitors are recommended alongside angiotensin cotransporter enzyme-inhibitor or angiotensin receptor blockers therapy for individuals with an albumin-creatinine ratio >30 mg/mmol and considered for those with an albumin-creatinine ratio in the range of 3–30 mg/mmol (National Institute for Health and Care Excellence, 2022a).

Glucagon-like peptide 1 and combined glucagon-like peptide 1/glucose-dependent insulinotropic peptide receptor agonists offer large reductions in haemoglobin A1C levels and substantial weight reduction. They are usually considered when triple oral therapy has not achieved the necessary haemoglobin A1C target and when weight loss is a priority. In type 2 diabetes, they hold an advantage over a basal insulin as the first injectable therapy because they:

achieve at least as large a reduction in haemoglobin A1C
are available as a once-weekly formulation
carry a low risk of hypoglycaemia
induce weight loss

A daily oral preparation of the glucagon-like peptide 1 receptor agonist, semaglutide, has been developed with stringent administration requirements.

Insulin can be used for glycaemic management in type 2 diabetes when other medications are insufficient, poorly tolerated or contraindicated.

Insulin use

A basal bolus insulin regimen is favoured for type 1 diabetes (National Institute for Health and Care Excellence, 2022a). In other forms of diabetes, including type 2 diabetes, a basal insulin is often the starting point, but this can progress to a two–three times daily mixed insulin regimen or a basal-bolus insulin regimen.

Porcine and bovine insulins have been largely superseded by human insulins produced by recombinant DNA technology. Analogue insulins in which the structure of human insulins has been altered to provide favourable pharmacokinetic properties are increasingly used. As a result, very long-acting basal insulin analogues and ultra-rapid acting prandial insulin analogues have been developed recently.

Patient education and empowerment are key to the success of insulin therapy. Essential points to be covered include:

injection technique
sharps disposal
blood glucose monitoring
self-adjustment of insulin dose
recognition and response to hypoglycaemia
sick day management rules
insurance and driving implications
point of contact if problems occur

Continuous subcutaneous insulin infusion (CSII, ‘pump’ therapy) has been demonstrated to improve levels of glycaemia and reduce the risk of severe hypoglycaemia compared to multiple daily insulin injections (Subramanian et al, 2024).

Hybrid closed loop systems, also referred to as the artificial pancreas, allow data from the continuous glucose monitor to direct insulin delivery from an insulin pump by means of a control algorithm adapted to an individual’s insulin requirements. Benefits have been demonstrated in improved glycaemic outcomes and quality of life (Subramanian et al, 2024).

Managing hypoglycaemia

People using insulin to manage their diabetes should use a fast-acting source of glucose (eg dextrose gel or tablets, jelly babies, honey or jam, sweetened fruit juice) to counter hypoglycaemia. This should be repeated after 10 minutes if there is no clinical improvement, or if blood glucose levels remain less than 4 mmol/L. Consumption of a longer-acting carbohydrate (eg sandwich, banana, cereal bar) helps to prevent recurrence of hypoglycaemia (National Institute for Health and Care Excellence, 2022a).

If hypoglycaemia results in a decreased level of consciousness, intramuscular glucagon administered by a family member or friend who has been shown how to use it is recommended. Beyond this, urgent medical attention is required.

Bariatric surgery for people with type 2 diabetes

For people with type 2 diabetes, bariatric surgery can achieve significant weight loss and diabetes remission, particularly with recent-onset type 2 diabetes (National Institute for Health and Care Excellence, 2022a). Weight loss referral should be made to a multidisciplinary team who will incorporate lifestyle changes and behavioural interventions.

Managing other forms of diabetes

The management for different types of diabetes are usually based on guidelines for type 1 and type 2 diabetes. Management of lifestyle and cardiovascular risk generally applies to all forms of diabetes.

For certain cases of MODY, first-line pharmacotherapy may involve prescription of sulphonylurea, although ultimately insulin may be required (Urakami, 2019).

Oral hypoglycaemic agents can be given in cases of pancreatogenic diabetes, but insulin is needed in most cases to deal with insulin deficiency and may be required from the outset. Pancreatic enzyme replacement therapy is likely to be needed alongside treatment for diabetes (Gupte et al, 2018).

Managing cardiovascular risk

Treating hypertension

Raised blood pressure is a major risk factor for both macrovascular and microvascular disease. Diabetes and hypertension commonly co-exist, especially in type 2 diabetes. See Table 1 for National Institute for Health and Care Excellence (2021; 2023) blood pressure targets.

Table 1. Blood pressure targets for people with diabetes
Condition	Clinic blood pressure (mmHg)
Type 1 or type 2 diabetes, <80 years old	<140/90
Type 1 or type 2 diabetes, ≥80 years	<150/90
Type 1 or type 2 diabetes with albumin-creatinine ratio >70 mg/mmol	<130/80
From: National Institute for Health and Care Excellence, 2021; 2023

Angiotensin converting enzyme inhibitors and angiotensin receptor blockers are first-line antihypertensive agents for people with diabetes, because of their cardio-renal benefits (Table 2). An angiotensin receptor blocker is preferred to an angiotensin converting enzyme inhibitor in people with Black African or African-Caribbean ethnicity, because it is less likely to induce coughing and angioedema (National Institute for Health and Care Excellence, 2024a; 2024b).

For people with chronic kidney disease and type 1 or type 2 diabetes, angiotensin converting enzyme inhibitors and angiotensin receptor blockers should be offered for renoprotection, but not in combination if albumin-creatinine ratio is ≥3mg/mmol whether or not hypertension is present, with up-titration to the highest possible dose (National Institute for Health and Care Excellence, 2021).

Table 2. Stepwise approach to treating hypertension in adults with diabetes
Step in treatment algorithm	Intervention	Details
Step 1	ACE-I, eg ramipril or ARB (eg losartan)	Choose ARB for people with Black African or African-Caribbean ethnicity
Step 2	Dihydropyridine CCB, eg amlodipine or thiazide-like diuretic (eg indapamide)	Other cardiovascular co-morbidities may direct selection between these two choices
Step 3	ACE-I/ARB, CCB and thiazide-like diuretic	Add agent not used in step two
Step 4	MRA, eg spironolactone or beta-blocker (eg bisoprolol) or alpha blocker (eg doxazosin)	Avoid MRA if blood potassium levels are >4.5 mmol/L
From: National Institute for Health and Care Excellence, 2023. ACE-I=angiotensin converting enzyme inhibitor; ARB=angiotensin receptor blocker; CCB=calcium channel blocker; MRA=mineralocorticoid receptor antagonist

Smoking cessation

People who smoke should be encouraged and supported to quit smoking, to reduce the risk of cardiovascular disease and other problems. Adults who do not smoke should be advised never to start.

Resources

American Diabetes Association. Diabetes care: standards of care in diabetes – 2024. 1st issue. Arlington County (VA): American Diabetes Association; 2024

Diabetes UK. Diabetes UK: know diabetes, fight diabetes. 2025. https://www.diabetes.org.uk/ (accessed 20 February 2025)

Dyson PA, Twenefour D, Breen C et al. Diabetes UK evidence-based nutrition guidelines for the prevention and management of diabetes. Diabet Med. 2018;35(5):541–547. https://doi.org/10.1111/dme.13603

Ewald N, Hardt PD. Diagnosis and treatment of diabetes mellitus in chronic pancreatitis. World J Gastroenterol. 2013;19(42):7276–7281. https://doi.org/10.3748/wjg.v19.i42.7276

Gupte A, Goede D, Tuite R, Forsmark CE. Chronic pancreatitis. BMJ. 2018;361:k2126. https://doi.org/10.1136/bmj.k2126

Hattersley AT, Greeley SAW, Polak M et al. ISPAD Clinical Practice Consensus Guidelines 2018: The diagnosis and management of monogenic diabetes in children and adolescents. Pediatr Diabetes. 2018;19 Suppl 27:47–63. https://doi.org/10.1111/pedi.12772

Lean ME, Leslie WS, Barnes AC et al. Primary care-led weight management for remission of type 2 diabetes (DiRECT): an open-label, cluster-randomised trial. Lancet. 2018;391(10120):541–551. https://doi.org/10.1016/S0140-6736(17)33102-1

Lean MEJ, Leslie WS, Barnes AC et al. Durability of a primary care-led weight-management intervention for remission of type 2 diabetes: 2-year results of the DiRECT open-label, cluster-randomised trial. Lancet Diabetes Endocrinol. 2019;7(5):344–355. https://doi.org/10.1016/S2213-8587(19)30068-3

Morris D, Moulik P. Case report: pancreatic cancer – assessing diabetes in a thin elderly person. Diabetes & Primary Care. 2024;26(1):5–9

National Institute for Health and Care Excellence. Chronic kidney disease: assessment and management. 2021. https://www.nice.org.uk/guidance/ng203 (accessed 20 February 2025)

National Institute for Health and Care Excellence. Type 1 diabetes in adults: diagnosis and management. 2022a. https://www.nice.org.uk/guidance/ng17 (accessed 20 February 2025)

National Institute for Health and Care Excellence. Type 2 diabetes in adults: management. 2022b. https://www.nice.org.uk/guidance/ng28 (accessed 20 February 2025)

National Institute for Health and Care Excellence. Hypertension in adults: diagnosis and management. 2023. https://www.nice.org.uk/guidance/ng136 (accessed 20 February 2025)

National Institute for Health and Care Excellence. Diabetes – type 2. 2024a. https://cks.nice.org.uk/topics/diabetes-type-2/ (accessed 20 February 2025)

National Institute for Health and Care Excellence. Diabetes – type 1. 2024b. https://cks.nice.org.uk/topics/diabetes-type-1/ (accessed 20 February 2025)

National Institute for Health and Care Excellence. Obesity: identification, assessment and management. 2025. https://www.nice.org.uk/guidance/ng246 (accessed 20 February 2025)

Subramanian S, Khan F, Hirsch IB. New advances in type 1 diabetes [published correction appears in BMJ. 2024;385:q1224. https://doi.org/ 10.1136/bmj.q1224]. BMJ. 2024;384:e075681. https://doi.org/10.1136/bmj-2023-075681

Urakami T. Maturity-onset diabetes of the young (MODY): current perspectives on diagnosis and treatment. Diabetes Metab Syndr Obes. 2019;12:1047–1056. https://doi.org/10.2147/DMSO.S179793

World Health Organization. Diabetes. 2025. https://www.who.int/health-topics/diabetes#tab=tab_1 (accessed 20 February 2025)