Type 2 Diabetes: Causes, Complications and Treatment

Type 2 Diabetes: Causes, Complications and Treatment

Type 2 diabetes mellitus (T2DM) is the most common form of diabetes. The IDF Diabetes Atlas 10th edition estimated that approximately 537 million adults aged 20–79 had diabetes in 2021 and projected 783 million by 2045. These historical figures cover diabetes overall, not type 2 diabetes alone. It is the leading cause of kidney failure, adult-onset blindness, and non-traumatic lower limb amputation, and a major driver of cardiovascular disease and stroke.

China has the largest absolute burden of diabetes of any country — an estimated 140 million adults with diabetes, and a further 350 million with prediabetes. The scale of this epidemic makes diabetes management one of the most urgent healthcare priorities in the region.

What Is Type 2 Diabetes?

Type 2 diabetes is characterised by chronic hyperglycaemia — persistently elevated blood glucose — resulting from two core defects:

1. Insulin resistance: target tissues (muscle, liver, fat) fail to respond normally to insulin, requiring the pancreas to produce more insulin to achieve the same glucose-lowering effect
2. Progressive beta-cell failure: the insulin-secreting beta cells of the pancreatic islets become exhausted and gradually fail, unable to compensate for the increased insulin demand

Unlike type 1 diabetes (an autoimmune condition that destroys insulin-producing beta cells and can leave little or no insulin production), type 2 diabetes has partial insulin production — though this declines over years — and is strongly driven by lifestyle and genetic factors.

Causes and Risk Factors

Modifiable Risk Factors

Overweight and obesity — central (abdominal) obesity is the strongest modifiable risk factor. Visceral adipose tissue releases fatty acids and inflammatory adipokines that promote hepatic insulin resistance and impair beta-cell function. Each 1 kg/m² increase in BMI increases T2DM risk by approximately 9%.

Physical inactivity — skeletal muscle accounts for approximately 80% of postprandial glucose uptake; inactivity impairs glucose transport into muscle independently of weight.

Diet — high intake of refined carbohydrates, sugar-sweetened beverages, processed meats, and saturated fats increases risk; Mediterranean and DASH diets are protective.

Prediabetes — impaired fasting glucose (6.1–6.9 mmol/L) or impaired glucose tolerance (2-hour glucose 7.8–11.0 mmol/L after oral glucose load); 25–50% of individuals with prediabetes progress to T2DM within 5 years without intervention.

Gestational diabetes — diabetes during pregnancy substantially raises subsequent T2DM risk.

Non-Modifiable Risk Factors

• Age (risk rises sharply after 45)
• Family history (first-degree relative with T2DM: 3× increased risk)
• Ethnicity (South Asian, East Asian, Hispanic, Black African: earlier onset, higher risk at lower BMI)
• Polycystic ovary syndrome (PCOS)
• Prior gestational diabetes

Symptoms

Type 2 diabetes often develops insidiously — many patients are diagnosed incidentally on routine blood tests or at the time of a complication.

Classic hyperglycaemic symptoms (occur when glucose is high — typically >10–15 mmol/L):

• Polyuria — excessive urination (osmotic diuresis: glucose in urine draws water)
• Polydipsia — excessive thirst (responding to dehydration from polyuria)
• Polyphagia — increased hunger despite eating
• Unexplained weight loss (glucose lost in urine; cellular starvation despite high blood glucose)
• Fatigue — cells cannot utilise glucose effectively without insulin
• Blurred vision — osmotic changes in the lens with high glucose

Other common presentations:

• Recurrent infections (urinary tract, skin, thrush) — glucose-rich environment promotes bacterial and fungal growth
• Slow-healing wounds
• Peripheral tingling or numbness (early diabetic neuropathy)
• Erectile dysfunction

Diagnosis

Diabetes is diagnosed by any of:

Test	Diabetes Threshold	Prediabetes Range
Fasting plasma glucose	≥7.0 mmol/L	6.1–6.9 mmol/L
2-hour glucose (OGTT)	≥11.1 mmol/L	7.8–11.0 mmol/L
Random plasma glucose + symptoms	≥11.1 mmol/L	—
HbA1c	≥48 mmol/mol (6.5%)	42–47 mmol/mol (6.0–6.4%)

A single abnormal result in an asymptomatic patient requires confirmation with a repeat test on a different day. HbA1c reflects average blood glucose over the preceding 2–3 months and is the preferred monitoring tool.

Long-Term Complications

Chronic hyperglycaemia damages blood vessels and nerves throughout the body through several mechanisms — protein glycation, oxidative stress, inflammation, and polyol pathway activation.

Microvascular Complications (small vessel disease)

• Diabetic retinopathy — the most common cause of blindness in working-age adults; affects virtually all T1DM patients and 60–80% of T2DM patients after 20 years; annual eye screening is essential
• Diabetic nephropathy — progressive kidney damage; 20–40% of diabetic patients develop chronic kidney disease; leading cause of end-stage renal disease requiring dialysis
• Diabetic neuropathy — damage to peripheral nerves; affects 50% of patients with long-standing diabetes; causes peripheral sensory neuropathy (tingling, numbness, pain in feet and hands), autonomic neuropathy (erectile dysfunction, gastroparesis, orthostatic hypotension), and Charcot foot

Macrovascular Complications (large vessel disease)

• Cardiovascular disease — the leading cause of death in diabetic patients; 2–4× increased risk of myocardial infarction and stroke compared to non-diabetic individuals
• Peripheral arterial disease — reduced circulation to the limbs; contributes to diabetic foot ulcers and the risk of amputation

Diabetic Foot

Peripheral neuropathy (loss of protective sensation) combined with peripheral arterial disease (poor healing) creates the diabetic foot — susceptible to unrecognised trauma, ulceration, infection, and osteomyelitis. Annual foot inspection is mandatory.

Treatment

Lifestyle Intervention

Weight loss — can improve glycaemic control and lead to remission in some people with T2DM. DiRECT enrolled adults with relatively recent type 2 diabetes who were not using insulin. In its 1-year analysis across both study groups, remission was observed in 57% of participants who lost 10–15 kg and 86% of those who lost at least 15 kg. These are separate observed weight-loss strata, not a guaranteed response to a prescribed amount of weight loss. Remission used HbA1c <48 mmol/mol after at least 2 months without glucose-lowering medication; this does not mean stopping other necessary medicines. Even 5–10% weight loss significantly improves glycaemic control.

Physical activity — 150 minutes/week of moderate aerobic exercise (brisk walking) reduces HbA1c by 0.5–1%, independent of weight loss. Resistance training additionally improves insulin sensitivity.

Dietary modification — choose an individualised, sustainable eating plan, which may include a Mediterranean or lower-carbohydrate pattern, with less refined carbohydrate and fewer sugar-sweetened beverages and more vegetables and fibre. Very-low-calorie diets require a clinically assessed indication, a specialist-supervised programme and review of medicines, including glucose-lowering treatment. They are not a routine self-directed or long-term diet.

Glucose-Lowering Medications

Treatment is typically stepped up over time as beta-cell function declines.

Metformin — first-line in most guidelines; reduces hepatic glucose output; lowers HbA1c by 1–2%; weight-neutral or modest weight loss; 60+ years of evidence; cheap; the backbone of T2DM pharmacotherapy.

GLP-1 receptor agonists (semaglutide — Ozempic/Wegovy; liraglutide — Victoza/Saxenda; dulaglutide — Trulicity; exenatide):

• Stimulate glucose-dependent insulin secretion, suppress glucagon, slow gastric emptying, reduce appetite
• HbA1c reduction 1–2%; significant weight loss (5–15% with semaglutide)
• Cardiovascular outcome evidence is specific to the medicine and studied population. Benefits shown for liraglutide, semaglutide and dulaglutide in LEADER, SUSTAIN-6 and REWIND should not be assumed for every GLP-1 receptor agonist, including exenatide.
• Available as weekly subcutaneous injection (semaglutide) or daily/weekly pens
• For cardiovascular disease or obesity, treatment is individualised; select an agent with demonstrated benefit for the relevant condition rather than assuming all medicines in this group have the same evidence.

SGLT-2 inhibitors (empagliflozin — Jardiance; dapagliflozin — Forxiga; canagliflozin — Invokana):

• Block glucose reabsorption in the kidneys, causing glycosuria (glucose lost in urine)
• HbA1c reduction 0.7–1%; weight loss 2–3 kg; blood pressure reduction
• Significant heart failure prevention and renoprotection (EMPA-REG, DECLARE, CREDENCE trials)
• Preferred in patients with heart failure or chronic kidney disease

DPP-4 inhibitors (sitagliptin — Januvia; saxagliptin; vildagliptin):

• Prolong endogenous GLP-1 action; glucose-dependent; weight-neutral
• HbA1c reduction 0.5–1%; well tolerated; convenient oral tablets

Sulfonylureas (glibenclamide, gliclazide, glipizide):

• Stimulate insulin secretion regardless of glucose level; risk of hypoglycaemia and weight gain
• Inexpensive; still widely used but falling out of favour with newer agents

Thiazolidinediones (pioglitazone):

• Improve insulin sensitivity; durable effect; weight gain and fluid retention limit use

Insulin therapy:

• Insulin may be needed when other treatment does not achieve individualised glycaemic goals, or when symptoms or severe hyperglycaemia make insulin appropriate. The clinician chooses the regimen and monitoring plan.
• Basal insulin (for example, glargine, detemir or degludec) helps control fasting glucose. Dosing frequency depends on the preparation and the individual prescription; detemir may be given once or twice daily. Follow the prescribed product instructions rather than assuming that every basal insulin is once daily.
• Premixed insulin — twice-daily injections; convenient but less flexible
• A basal-bolus regimen combines background and mealtime insulin and may be appropriate for some people. Marked hyperglycaemia requires prompt clinical assessment, but does not mean everyone needs this particular multiple-injection regimen; selection depends on severity, symptoms, other treatment and individual circumstances.

Target HbA1c

Patient Group	HbA1c Target
Most adults with T2DM	<53 mmol/mol (7%)
Young, fit, no complications	<48 mmol/mol (6.5%)
Elderly, frail, hypoglycaemia risk	<58–64 mmol/mol (7.5–8%)
Established cardiovascular disease	<53 mmol/mol; use GLP-1 or SGLT-2
Chronic kidney disease	Individualised HbA1c target and monitoring; an SGLT-2 inhibitor with demonstrated kidney or cardiovascular benefit may be appropriate when eligible. The specific medicine depends on kidney function, contraindications and the individual treatment plan.

Cardiovascular and Renal Risk Reduction

Glycaemic control alone is insufficient — the majority of diabetes-related mortality is cardiovascular:

• Statin therapy — eligibility, treatment intensity and LDL cholesterol goals depend on age, overall cardiovascular risk and whether atherosclerotic cardiovascular disease is established. The treating clinician should apply current risk-specific guidance, account for tolerability and reassess response; the same LDL target does not apply to everyone with diabetes.
• Antihypertensive therapy — individualised blood-pressure target, generally <130/80 mmHg when safely attainable; the choice of medicine depends on albuminuria, kidney function, cardiovascular conditions, pregnancy status and tolerability. An ACE inhibitor or ARB is not automatically preferred solely because a person has diabetes
• Aspirin — low-dose for secondary prevention in those with established CVD
• Smoking cessation — stopping smoking helps reduce cardiovascular risk; ask the care team for cessation support

Bariatric / Metabolic Surgery

Metabolic surgery, such as gastric bypass or sleeve gastrectomy, may improve glucose control and lead to remission in selected people with type 2 diabetes and obesity. Eligibility requires specialist assessment under current applicable guidance, including previous treatment, operative risks and long-term follow-up needs. Remission rates and durability vary, and diabetes can recur. Compare treatment options individually rather than describing surgery as universally superior to all medicines. Mechanisms include weight loss, gut hormone changes, and changes in bile acid signalling.

Diabetes Care in China

China's diabetes and endocrinology centres offer:

• Assessment and follow-up: ask the treating team which glucose tests, kidney and cardiovascular checks and complication assessments are appropriate for the individual case.
• Team and monitoring: confirm the specialists and education support involved and whether a proposed continuous glucose monitor is suitable, available and supported for your visit.
• Metabolic surgery: specialist assessment must establish suitability, the proposed procedure, individual risks and follow-up; do not infer outcomes from a centre’s location or an unverified comparison with other centres.
• Medicines: confirm the exact product, local indication, suitability and current supply with the hospital; do not assume that all basal insulins or a domestic version are available.
• Costs and language support: obtain a current written hospital quote and confirm the language of appointments, consent, reports and follow-up, including what separate coordination support covers. No general saving against another country or entirely English clinical pathway is assured.

Contact a PriumCare care navigator to arrange a diabetes assessment, medication review, or metabolic surgery consultation.

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Medical content based on MSD Manuals and international diabetes guidelines (ADA Standards of Care 2025). Evidence reviewed 2025.

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Targeted editorial source check — 26 October 2026: Only the blood-pressure unit and safety qualification, smoking-cessation wording and medication scope of remission were checked against the ADA cardiovascular guidance and international remission consensus. The trial outcome figures elsewhere in the paragraph were not reassessed in this targeted update. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.

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Targeted editorial source check — 26 October 2026: Only the population and date attached to the historical IDF diabetes estimates, the product-dependent frequency of basal insulin, and the need for current risk-specific lipid treatment were checked against IDF explanatory information, U.S. insulin detemir labeling and the 2026 AHA dyslipidemia guideline summary. The historical figures are not a new prevalence estimate. Product labeling and individual treatment decisions must be checked with the prescribing team. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.

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Targeted editorial source check — 26 October 2026: Only the CKD row’s need for individualised glucose targets and medicine selection, and the metabolic-surgery paragraph’s eligibility and remission/comparison wording, were checked against KDIGO diabetes and CKD guidance, NIDDK surgery information and the ARMMS-T2D trial report. These sources do not establish one treatment or guaranteed remission for every patient. This is not a whole-article medical review, adds no named clinical reviewer and retains the original publication date.

Scoped editorial source check — 26 October 2026: The agent-specific cardiovascular evidence and insulin-selection statements above were checked against the sources below. This limited correction is not a whole-article medical review.

• https://pmc.ncbi.nlm.nih.gov/articles/PMC12690185/

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Targeted editorial source check — 26 October 2026: The summary’s population wording, supervision and medicine review for very-low-calorie diets, and institution-specific service assertions were checked against IDF historical estimate information, NIDDK type 2 diabetes information and NICE dietary guidance. Historical all-diabetes figures are not a new type-2-only prevalence estimate. Actual hospital products, prices and language arrangements require confirmation. This is not a whole-article medical review, does not verify every retained trial or risk statistic and retains the original publication date.

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Targeted editorial source check — 26 October 2026: Only the type-1 beta-cell comparison and DiRECT population, remission definition and separate weight-loss strata were checked against NIDDK information and the original DiRECT trial report. Trial strata are not individual predictions or instructions to stop prescribed medicines. This is not a whole-article medical review, does not verify other retained statistics or treatment statements and retains the original publication date.

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Targeted editorial source check — 26 October 2026: Only the selection of blood-pressure medicines was checked against the primary reference. This is not a whole-article medical review, does not establish local hospital availability and retains the original publication date.