Prediabetes is a critical — and largely reversible — stage between normal blood sugar and type 2 diabetes. An estimated 5–7 million people in the UK are living with prediabetes, and the majority are unaware of it. Understanding what it is and acting early can make the difference between developing type 2 diabetes and avoiding it entirely.
What Is Prediabetes?
Prediabetes is defined by blood glucose levels that are above normal but not yet high enough for a diabetes diagnosis. The key diagnostic thresholds are:
- HbA1c: 42–47 mmol/mol (6.0–6.4%)
- Fasting blood glucose: 5.5–6.9 mmol/L (impaired fasting glucose)
- 2-hour glucose tolerance test: 7.8–11.0 mmol/L (impaired glucose tolerance)
Different countries and organisations use slightly different cut-offs — your GP will advise on which thresholds apply in your case.
What Causes Prediabetes?
Prediabetes develops when the body's cells become progressively less responsive to insulin (insulin resistance), and the pancreas can no longer fully compensate by producing more insulin. The root causes are multifactorial:
- Excess body fat — particularly visceral fat around the abdomen — releases inflammatory signals that impair insulin signalling
- Physical inactivity — muscle is the body's primary glucose-storage organ; less muscle mass means less capacity
- Poor dietary patterns — high in refined carbohydrates, ultra-processed foods, and sugary drinks
- Chronic sleep deprivation and stress — both elevate cortisol, which raises blood glucose
- Genetics and ethnicity — South Asian, Black African, and Black Caribbean backgrounds carry a 2–4x higher risk, partly due to differences in fat distribution and insulin secretion
- Age — risk increases significantly after 40
Can Prediabetes Be Reversed?
Yes — in many cases, prediabetes can be fully reversed. The evidence is robust: lifestyle change is more effective than medication (metformin) for prevention in most groups. The three most impactful interventions are:
- Weight loss: Losing 5–7% of body weight (around 4–5kg for someone weighing 75kg) reduces progression risk by over 50% in clinical trials
- Physical activity: 150 minutes of moderate-intensity exercise per week significantly improves insulin sensitivity
- Dietary change: Reducing refined carbohydrates and ultra-processed foods while increasing fibre, vegetables, and lean protein
These changes do not need to be drastic. Small, consistent improvements — a daily walk, fewer sugary drinks, an extra portion of vegetables — compound meaningfully over time. Your GP can refer you to the NHS Diabetes Prevention Programme, which provides free structured support.
Getting Tested
Because prediabetes typically has no symptoms, testing is the only way to know. Ask your GP for a blood glucose test if you are over 40, have a BMI above 25 (or above 23 if South Asian), have a family history of type 2 diabetes, or have previously had gestational diabetes. In England, you can also check your risk in 3 minutes at riskscore.diabetes.org.uk.