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" (high blood sugar that is not diabetes), "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 the extra insulin keeps blood sugar normal. Prediabetes is the point where the pancreas can no longer keep up 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, the fat packed around the organs).
• 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 (also known as 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.
• Being very thirsty and passing a lot of urine are not usual in prediabetes. They suggest blood sugar has moved into 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%).¹
• A fasting blood glucose of 5.5–6.9 mmol/L (the range NICE uses for high risk; the World Health Organization's 'impaired fasting glucose' range is narrower, 6.1–6.9 mmol/L).^1,2
• On an oral glucose tolerance test (you drink a measured sugary drink and blood is taken two hours later), a result of 7.8–11.0 mmol/L (impaired glucose tolerance).²

Exact cut-offs vary slightly between guidelines. For example, the American Diabetes Association begins the prediabetes range at an HbA1c of 39 mmol/mol (5.7%), and uses a lower fasting glucose threshold of 5.6 mmol/L.² 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. A focus on building meals with plenty of protein and non-starchy vegetables can be helpful, with starchy carbohydrate such as bread, rice, pasta and potatoes reduced, or adjusted to the amount that suits you. Try this as a starting point and adjust based on how you feel and your blood sugar readings. The 28 Day Plan framework may be a useful approach.

Movement

Aim for at least 150 minutes of moderate activity a week.³ A walk after meals is particularly useful for reducing blood-sugar rises. Add resistance (strengthening) sessions of 20 to 30 minutes at least twice a week to build muscle, which takes up glucose, and break up long periods of sitting.³

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. NICE advises a repeat blood test at least once a year for people in this range, and a check of weight or BMI.¹ You can also use a glucose sensor worn on the arm (a continuous glucose monitor) to see how your blood sugar responds to individual meals.

Other non-drug options

Some non-drug options have supporting evidence. These are additions to lifestyle change, not replacements, and are 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 only glucose-lowering medicine NICE suggests considering in prediabetes. It is for people whose blood results keep worsening despite an intensive lifestyle programme, or who cannot take part in one, particularly if their body mass index (BMI) is over 35.¹
• Metformin lowers blood sugar and modestly reduces progression to diabetes, though lifestyle change is generally more effective. In the US Diabetes Prevention Program, lifestyle change cut the rate of new diabetes by 58% over about three years and metformin by 31%.⁴ A smaller but still significant benefit was seen 15 years later.⁵
• Modified-release metformin is licensed in the UK, for adults aged 18 to 74, to reduce the risk of or delay type 2 diabetes in people at high risk whose blood sugar keeps rising despite three to six months of lifestyle change. Any other use in prediabetes is "off-label": a doctor can still prescribe it, using their own judgement.¹
• Weight-loss medicines, including the newer GLP-1-based injections (such as semaglutide and tirzepatide), may be an option where excess weight is the main driver. Whether they are suitable for you depends on current guidelines and your clinician's advice.
• Your doctor may also treat raised blood pressure or blood fats (lipids) to lower your risk of heart attack and stroke.

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.⁶ The insulin resistance that leads to prediabetes can cause many health and wellbeing challenges.

Some older, slimmer people, often with low muscle mass, find their prediabetes stays stable for years rather than progressing, especially with the nutrition approaches above.

But for many people prediabetes is often reversible, and acting early reduces the chance of developing diabetes and the complications that can follow. In follow-up studies (mostly using glucose tests rather than HbA1c), between a third and over half of people with prediabetes had returned to normal blood sugar within one to five years.⁶ 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