What Is Insulin Resistance? Causes and NHS Advice

Insulin resistance is a common metabolic condition in which the body's cells stop responding properly to insulin, causing the pancreas to produce ever-increasing amounts to compensate. Over time, this disrupts blood glucose regulation and raises the risk of prediabetes, type 2 diabetes, cardiovascular disease and fatty liver disease. Despite affecting millions of people in the UK, it often causes no obvious symptoms in its early stages, making awareness of risk factors and routine testing essential. This article explains what insulin resistance is, what causes it, how it is diagnosed on the NHS, and when to seek medical advice.

What is insulin resistance and how does it affect your body?

Insulin resistance occurs when cells fail to respond to insulin, so the pancreas produces more, raising both glucose and insulin levels. Over time this can cause fatty liver disease, prediabetes and type 2 diabetes.

Insulin resistance is a condition in which the body's cells do not respond effectively to insulin, meaning the hormone cannot do its job of moving glucose from the bloodstream into cells for energy. Insulin is produced by the pancreas and acts like a key, unlocking cells so they can absorb glucose. When cells become resistant, the pancreas compensates by producing more insulin, leading to higher circulating levels of both glucose and insulin over time.

This disruption affects multiple organ systems. In the liver, excess glucose is converted to fat, contributing to non-alcoholic fatty liver disease (NAFLD), also referred to in newer clinical literature as metabolic dysfunction-associated steatotic liver disease (MASLD). In muscle tissue, reduced glucose uptake impairs energy metabolism. In fat cells, particularly around the abdomen, resistance promotes further fat storage and inflammation, creating a cycle that worsens the condition.

Over time, if the pancreas cannot keep up with the demand for extra insulin, blood glucose levels rise persistently. This progression can lead to prediabetes and, if unaddressed, to type 2 diabetes. Insulin resistance is also closely linked to a cluster of metabolic abnormalities known as metabolic syndrome, which includes raised blood pressure, abnormal cholesterol levels and central obesity.^[1] Understanding this mechanism is important because insulin resistance is often present for years before any formal diagnosis is made.

What causes insulin resistance and who is most at risk in the UK?

Visceral obesity and physical inactivity are the strongest modifiable causes. South Asian, Black African and Black Caribbean populations face higher risk at lower BMI thresholds, recognised in NICE guidance PH46.

Insulin resistance develops through a combination of genetic predisposition, lifestyle factors and underlying health conditions, with excess body fat, particularly visceral fat stored around the abdomen, being one of the strongest modifiable drivers. Physical inactivity reduces the ability of muscle cells to take up glucose, while diets high in refined carbohydrates and heavily processed foods are associated with elevated blood glucose and insulin levels, though the strength of this relationship varies between individuals.

Several groups in the UK face a higher risk. People of South Asian, Black African, Black Caribbean, Chinese, Middle Eastern and other Asian heritage develop insulin resistance and type 2 diabetes at lower body mass index thresholds than white European populations, a pattern recognised in NICE public health guidance (NICE PH46).^[4][3] NICE recommends using a lower BMI threshold of 27.5 kg/m² rather than 30 kg/m² when assessing obesity-related risk in these groups.

Other risk factors include:

• Age over 40 (or over 25 in higher-risk ethnic groups, in line with NHS guidance)

• Polycystic ovary syndrome (PCOS), which is strongly associated with insulin resistance in women^[5][6]

• A family history of type 2 diabetes

• Gestational diabetes during a previous pregnancy

• Obstructive sleep apnoea, which disrupts hormonal regulation

• Certain medications, including long-term corticosteroids and some antipsychotics, if you have been prescribed any of these, do not stop or alter your medication without speaking to your clinician first

Chronic stress and poor sleep quality also impair insulin sensitivity through their effects on cortisol and other hormones.^[15] Because many of these risk factors interact, a person may have several simultaneously, compounding their overall risk. Identifying modifiable factors early offers the best opportunity for intervention before the condition progresses.

How do doctors diagnose insulin resistance on the NHS?

NHS diagnosis uses HbA1c, fasting plasma glucose and lipid profiles rather than a direct insulin resistance test. Prediabetes is defined as HbA1c 42 to 47 mmol/mol or fasting glucose 6.1 to 6.9 mmol/l.

There is no single NHS test that directly measures insulin resistance in routine clinical practice; instead, doctors use a combination of blood tests and clinical assessment to identify it and its consequences. The most commonly used markers are fasting plasma glucose, HbA1c (a measure of average blood glucose over approximately three months) and a fasting lipid profile. Raised triglycerides alongside low HDL cholesterol are a characteristic pattern associated with insulin resistance.

In England, NHS guidance defines prediabetes as an HbA1c of 42 to 47 mmol/mol or a fasting plasma glucose of 6.1 to 6.9 mmol/l, and diabetes as an HbA1c of 48 mmol/mol or above (or fasting plasma glucose of 7.0 mmol/l or above) on two separate occasions in the absence of symptoms, or once if symptoms are present. These thresholds are consistent with WHO and NICE criteria. An oral glucose tolerance test (OGTT) may be used when prediabetes or gestational diabetes is being evaluated; a two-hour plasma glucose of 7.8 to 11.0 mmol/l indicates impaired glucose tolerance.

The NHS Health Check programme, offered every five years to adults aged 40 to 74 in England who do not already have a relevant diagnosis, includes blood pressure measurement, cholesterol testing and a diabetes risk assessment.^[9] This is often the first point at which insulin resistance-related abnormalities are identified. Your GP may also use validated risk tools such as the Leicester Risk Assessment (available via Diabetes UK's Know Your Risk tool) or the QDiabetes score to estimate your likelihood of developing type 2 diabetes.

In some clinical settings, particularly where PCOS or metabolic syndrome is suspected, a fasting insulin level may be measured alongside fasting glucose to calculate a surrogate marker called HOMA-IR (Homeostatic Model Assessment of Insulin Resistance). This is not a standardised NHS diagnostic test, its interpretation varies between laboratories, and it should not be used alone to diagnose or guide treatment in routine NHS care.

If you are concerned about your metabolic health, speaking to your GP is the appropriate first step. They can arrange relevant blood tests and, where results suggest prediabetes, refer you to the NHS Diabetes Prevention Programme, a structured lifestyle intervention with good evidence for reducing progression to type 2 diabetes.^[13][14]

What are the symptoms and long-term health risks to watch for?

Insulin resistance is often symptom-free early on, but acanthosis nigricans, persistent fatigue and abdominal weight gain may occur. Long-term risks include type 2 diabetes, cardiovascular disease and fatty liver disease.

Insulin resistance itself often produces no obvious symptoms in its early stages, which is why it frequently goes undetected until blood tests reveal abnormal glucose or lipid levels. When symptoms do occur, they tend to be non-specific and can be caused by many other conditions; they are not diagnostic on their own and should prompt testing rather than self-diagnosis. These may include:

• Persistent fatigue, particularly after meals

• Difficulty concentrating or mental fogginess

• Increased hunger shortly after eating

• Weight gain around the abdomen, which may occur as part of the metabolic changes associated with insulin resistance

• Acanthosis nigricans, a darkening and thickening of the skin in folds such as the neck, armpits or groin, which reflects the effect of high insulin levels on skin cells

In women with PCOS, insulin resistance may contribute to irregular periods, excess hair growth and difficulty conceiving.

The long-term health risks are significant if insulin resistance is not addressed. The most direct consequence is progression to prediabetes and then type 2 diabetes, which itself carries risks of cardiovascular disease, kidney disease, nerve damage and sight loss. Insulin resistance is also associated with an increased risk of cardiovascular disease through its effects on blood pressure, cholesterol and inflammation.

NAFLD (also referred to as MASLD) is closely linked to insulin resistance and can progress to more serious liver disease in a minority of cases, according to NICE guidance on NAFLD (NG49).^[11][12] There is also emerging evidence of associations with certain cancers and with cognitive decline, though these relationships are still being studied and no firm causal conclusions can be drawn at this stage. Addressing insulin resistance through lifestyle change, and where appropriate medication, can help reduce these long-term risks, though the degree of benefit will vary between individuals.

When should you speak to a GP about insulin resistance?

Speak to your GP if you have risk factors such as a family history of type 2 diabetes, belong to a higher-risk ethnic group, or are aged 40 or over, even without symptoms. Urgent symptoms like extreme thirst or confusion require same-day contact.

You should speak to your GP about insulin resistance if you have one or more recognised risk factors and have not had a recent metabolic health check, particularly if you are aged 40 or over, have a family history of type 2 diabetes, or belong to an ethnic group with a higher baseline risk. You do not need to wait for symptoms to appear, as early identification allows for lifestyle interventions that can meaningfully reduce the risk of progression.

Contact your GP promptly if you notice any of the following:

• Unexplained weight gain, especially around the abdomen, that is not responding to dietary changes

• Persistent fatigue or difficulty concentrating that is affecting daily life

• Skin changes consistent with acanthosis nigricans

• Irregular periods or signs of PCOS in women of reproductive age

• A previous diagnosis of gestational diabetes, which significantly raises future risk

If you have already been told your blood glucose or HbA1c is in the prediabetes range, follow-up with your GP is important to discuss referral to the NHS Diabetes Prevention Programme and to monitor your results over time.

For urgent symptoms such as extreme thirst, frequent urination, unexplained weight loss or blurred vision, which may suggest blood glucose has risen to diabetic levels, contact your GP as soon as possible or call NHS 111 for advice if your surgery is closed. If you or someone else experiences severe drowsiness, confusion, vomiting, or deep and laboured breathing, call 999 immediately, as these may indicate a serious hyperglycaemic emergency requiring urgent medical attention.

Managing insulin resistance typically involves structured lifestyle change, including increased physical activity, dietary modification and, where relevant, weight management support. Your GP can discuss whether any of these pathways, including referral to specialist services, are appropriate for your circumstances. Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support, for those exploring clinical options alongside lifestyle change.

Scientific References

1. Metabolic syndrome.
2. Type 2 diabetes: prevention in people at high risk (PH38).
3. Overweight and obesity management (NG246) – Identifying and assessing overweight, obesity and central adiposity.
4. Appendix A1: Summary of evidence from surveillance (PH46).
5. Polycystic ovary syndrome: assessment and management (GID-NG10436) – consultation comments and responses.
6. Polycystic ovary syndrome | Treatment summaries – BNF.
7. Punjabi NM et al. Obstructive sleep apnea is independently associated with insulin resistance. American Journal of Respiratory and Critical Care Medicine..
8. Diabetes | Treatment summaries – BNF.
9. NHS Health Check.
10. Hermanns-Lê T et al. Acanthosis nigricans associated with insulin resistance..
11. Metabolic dysfunction-associated steatotic liver disease (NG49).
12. Non-alcoholic fatty liver disease (NAFLD).
13. McManus E et al. Population level impact of the NHS Diabetes Prevention Programme..
14. Health matters: preventing Type 2 Diabetes.
15. Sleep loss as a cardiometabolic risk factor: a narrative review of clinical and public health implications. Journal of Clinical Sleep Medicine..

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