Prediabetes

Key points

What it is

Prediabetes is a state in which blood glucose (blood sugar) is raised above the normal range but has not yet reached the level used to diagnose type 2 diabetes. It sits partway between normal blood-sugar control and diabetes. You may also hear it called "non-diabetic hyperglycaemia", "impaired fasting glucose", or "impaired glucose tolerance", depending on which test identified it.

What causes it, and who is at risk

The underlying cause is usually insulin resistance, where the body's cells respond less readily to insulin, so the pancreas makes more of it to keep blood sugar controlled. For a time this compensation works and glucose stays normal. Prediabetes is the point at which it begins to fall behind and blood sugar starts to rise.

Several factors raise the risk, and many people have more than one:

• Carrying excess weight, especially around the middle (visceral fat).
• Lower muscle mass. This is a common contributor in older people.
• Physical inactivity and long periods of sitting.
• A diet high in sugar, refined carbohydrate and ultra-processed food.
• Increasing age.
• A family history of type 2 diabetes.
• Certain ethnic backgrounds (for example South Asian, African, African-Caribbean), often at a lower body weight.
• PMOS, polyendocrine metabolic ovarian syndrome (previously called PCOS).
• A past history of gestational diabetes.
• Poor sleep, shift work and chronic stress.
• Some medications, such as long-term steroids.

Symptoms and signs

The high sugar level in prediabetes usually causes no symptoms. This is why it may go unnoticed until it is found by chance on a blood test taken for another reason. However, there are other symptoms and signs of the insulin resistance that underlies it:

• A larger waistline or central weight gain, with greater difficulty losing weight.
• Acanthosis nigricans (dark, velvety patches of skin, often at the neck or armpits), or skin tags, which can both be signs of high insulin.
• Low energy and tiredness.
• Sometimes low mood.
• Higher blood pressure.
• If there is excess thirst and frequent urination it is more likely the blood sugar has moved in to the diabetes range.

How it is diagnosed

Prediabetes is diagnosed with a blood test, most often HbA1c (a measure of average blood sugar over the previous two to three months) or a fasting glucose. In the UK the commonly used thresholds are:

• HbA1c of 42–47 mmol/mol (6.0–6.4%).
• A fasting blood glucose in the impaired range (6.1–6.9 mmol/L).
• On an oral glucose tolerance test, a 2-hour glucose of 7.8–11.0 mmol/L (impaired glucose tolerance).

Exact cut-offs vary slightly between guidelines. For example, some international bodies begin the prediabetes range at an HbA1c of 39 mmol/mol (5.7%), and use a lower fasting glucose threshold of 5.6 mmol/L. The result is always interpreted by a clinician alongside a wider health assessment.

The metabolic health perspective

Prediabetes reflects early difficulty with metabolic health. The raised blood sugar is a sign of an underlying process, namely insulin resistance and the rising insulin levels that accompany it. The same factors often seen in other metabolic conditions are usually present, including a larger waist, fat building up in the liver, and an increased level of long-term body-wide inflammation. By the time it rises into the prediabetes range, the underlying strain has usually been developing for some years.

Because prediabetes is largely driven by lifestyle factors, it often responds well to lifestyle changes. Benefits can be achieved within weeks to a few months. Reducing foods that directly raise blood sugar, and building and using muscles to take up glucose, can reduce insulin resistance and bring blood sugar down. Prediabetes is therefore often considered a reversible condition if the correct lifestyle actions are taken. This is especially true for younger people.

Treatment and management

The aim is to make lifestyle changes to bring blood sugar back toward normal and to prevent progression to type 2 diabetes. This is effective for many people and often leads to significant wellbeing benefits such as more energy, a slimmer waist, and better blood pressure. Other non-drug measures and, in some cases, medication can support it. This is best done with the guidance of your healthcare team, who can also monitor your results over time.

Lifestyle and the Health Foundations

This is the most effective approach for most people.

Nutrition

Reduce sugar, sugary drinks, refined carbohydrate and ultra-processed food. Build meals around sources of protein (at least a palm-sized portion), fill most of the rest of the plate with non-starchy vegetables, and add natural fats for flavour. Treat starchy carbohydrate such as bread, rice, pasta and potatoes as an optional extra sized to you, rather than a fixed portion. Lowering the overall carbohydrate and insulin load is the key idea: some people find keeping total carbohydrate under about 130g a day is enough, while others, especially with more marked insulin resistance, do better going lower, toward 70g a day or less. These are starting points to test rather than fixed rules.

Movement

Aim for at least 150 minutes of moderate activity a week. A walk after meals is particularly useful for reducing blood-sugar rises. Add two to three resistance sessions of 20 to 30 minutes a week to build muscle, which takes up glucose, and break up long periods of sitting.

Sleep

Aim for adequate, regular sleep (most adults need seven to nine hours), as poor sleep worsens insulin resistance.

Stress

Reduce the chronic stress load where you can, as stress hormones raise blood sugar.

Environment

Set up your kitchen and routine so the healthy choice is the easier one.

Tracking your waist and re-checking your HbA1c over the following months is a simple way to follow your progress. You can also monitor your blood glucose with sensors, which show how your levels respond to individual meals.

Other non-pharmaceutical options

Some non-drug options have supporting evidence. These should be considered as complementary to the lifestyle changes, and usually best discussed with a clinician:

• Vitamin D3. Deficiency is common and is associated with insulin resistance. Correcting a genuine deficiency is sensible, though the direct effect on blood sugar is modest.
• Magnesium. Low levels are linked to insulin resistance, and supplementation may help modestly in those who are deficient.
• Other supplements. Some, such as berberine and (particularly in PMOS-related cases) inositol, have shown glucose-lowering effects in trials, though study quality varies and some can interact with medication. Others sometimes promoted, such as cinnamon or chromium, have weaker or less consistent evidence. These are best regarded as possible additions rather than substitutes for the basics. People should not take excessive amounts of any supplement.
• Stopping smoking and reducing alcohol. Both improve the overall metabolic picture and cardiovascular risk.

Medical and pharmaceutical treatments

• Metformin is the medication most often considered in prediabetes, particularly for people at higher risk or whose blood sugar continues to rise despite lifestyle change. It lowers blood sugar and modestly reduces progression to diabetes, though lifestyle change is generally more effective. It is not licensed for prediabetes in the UK, so where it is used for this it is prescribed off-label and at a clinician's discretion.
• Weight-loss medications, including the newer GLP-1 receptor-based treatments, are increasingly relevant where excess weight is the main driver. Their licensing and use are decided by a clinician and current guidelines.
• Where appropriate, related risk factors such as blood pressure and blood lipids (fats) may also be managed as part of reducing overall cardiovascular risk.

These are prescribed and monitored by a clinician; the above is a summary for understanding, not prescribing guidance.

Complications and outlook

Without changes, a significant proportion of people with prediabetes could go on to develop type 2 diabetes over the following years. The insulin resistance that leads to prediabetes can cause many health and wellbeing challenges.

Older people who are slimmer, usually with a low muscle mass (less body-wide muscle), may see the prediabetes remain stable over years, especially if they follow the helpful nutrition approaches.

But for many people prediabetes is often reversible, and acting early reduces the chance of developing diabetes and the complications that can follow. Many people return their blood sugar to the normal range. Where it is not fully reversed, slowing or halting the progression is still worthwhile.

When to see a doctor

• If you have been told you have prediabetes or a raised HbA1c, arrange follow-up so you can agree a plan and a schedule for monitoring.
• See a doctor promptly if you develop symptoms that can signal diabetes, such as excessive thirst, passing a lot of urine, unexplained weight loss, persistent fatigue or blurred vision.
• Speak with your clinician before starting supplements or making major dietary changes if you take medication, including for blood pressure or warfarin, as doses may need adjusting.

Summary