In pre-diabetes (impaired glucose tolerance, now usually referred to by doctors and nurses as non-diabetic hyperglycaemia), your blood sugar (glucose) is raised beyond the normal range. Whilst this raised glucose level is not so high that you have type 2 diabetes, you are at increased risk of developing type 2 diabetes when you have pre-diabetes.
What is pre-diabetes?
If you have pre-diabetes (impaired glucose tolerance), your blood sugar (glucose) is raised beyond the normal range but it is not so high that you have diabetes. However, if you have pre-diabetes you are at risk of developing type 2 diabetes.
Between 1 and 3 out of every 4 people with pre-diabetes will develop diabetes within ten years.
The World Health Organization (WHO) defines someone as having pre-diabetes if they have:
- A fasting blood glucose of less than 7 mmol/L; and
- A blood glucose of 7.8 mmol/L or more but less than 11.1 mmol/L after a two-hour oral glucose tolerance test.
However, the glucose tolerance test is rarely used now. The most commonly used test to identify pre-diabetes is now the HbA1c blood test. The WHO and the National Institute for Health and Care Excellence (NICE) have recommended that an HbA1c blood test level of 42-47 mmol/mol (6.0-6.4%) indicates a high risk of diabetes.
Impaired fasting glycaemia
If you have impaired fasting glycaemia, you are also thought to have an increased risk of developing diabetes.
Your risk of developing cardiovascular disease is also increased but this seems to be lower than if you have pre-diabetes (impaired glucose tolerance).
A person has impaired fasting glycaemia if they have:
- A fasting blood glucose between 6.1 to 6.9 mmol/L; and
- A blood glucose of less than 7.8 mmol/L after a two-hour oral glucose tolerance test.
NICE states that someone with a fasting blood glucose of 5.5-6.9 mmol/L is at high risk of developing type 2 diabetes.
Do I Have Diabetes?
Our quiz will help you discover whether you are exhibiting some of the symptoms and evaluate your risk.
People with pre-diabetes (impaired glucose tolerance) usually have no symptoms.
You are often found to have pre-diabetes after blood tests taken for another reason show that you have a raised blood sugar (glucose) level.
Sometimes, your doctor may suggest that a screening blood test should be taken to check your blood glucose because they are worried that you may have some risk factors for pre-diabetes or diabetes.
How common is pre-diabetes?
Many people have pre-diabetes (impaired glucose tolerance) and because there are no symptoms, they do not know that they have it. Diabetes UK estimates that around seven million people in the UK have pre-diabetes.
What causes pre-diabetes?
Pre-diabetes (impaired glucose tolerance) develops for the same reasons as type 2 diabetes (see above). There are various things that can increase your risk of developing pre-diabetes. They are the same risk factors as those for type 2 diabetes. They include:
- Being overweight or obese (most people with pre-diabetes are overweight or obese).
- Having a family history of diabetes. This refers to a close family member with diabetes - a mother, father, brother or sister.
- Doing little physical activity.
- Having other risk factors for cardiovascular disease such as high blood pressure or high cholesterol levels.
- If a woman has polycystic ovary syndrome and is also overweight.
- If you developed diabetes during pregnancy (called gestational diabetes).
How is pre-diabetes diagnosed?
Pre-diabetes is now most often diagnosed using a blood test called HbA1c. See the separate leaflet called Tests for Blood Sugar (Glucose) and HbA1c for more details.
An HbA1c value of 48 mmol/mol (6.5%) or above is required to diagnose diabetes. People with an HbA1c level of 42-47 mmol/mol (6.0-6.4%) are considered to have pre-diabetes because they are at increased risk of diabetes and cardiovascular disease.
Another test to diagnose pre-diabetes is the glucose tolerance test but this is much less often used now. Read more in the separate leaflet called Glucose Tolerance Test.
- Referral to the Diabetes Prevention Programme.
- Lifestyle changes such as diet and exercise.
There is increasing evidence that if pre-diabetes (impaired glucose tolerance) is treated, it becomes much easier to prevent or delay it progressing to type 2 diabetes. Also, it may be possible to prevent cardiovascular disease from developing.
It is also very important to have a regular blood test to recheck your blood sugar (glucose) level in case you develop diabetes. The frequency of the blood test will vary but you should discuss this with your doctor. A blood glucose test at least once each year is usually recommended.
Referral for help and support
The NHS in England has developed the NHS Diabetes Prevention Programme for people with pre-diabetes. This provides personalised support from a group of healthcare professionals.
If you are diagnosed with pre-diabetes and live in England, you should be offered referral to this service. It involves at least 13 sessions over about 9 months, each lasting 1-2 hours. You will be supported to set and achieve goals and make positive changes to reduce your risk of developing type 2 diabetes. Most of the sessions will be run as face-to-face groups with other people who also have pre-diabetes and led by one or more experts.
Lifestyle changes have been found to be the most effective way to stop pre-diabetes from developing into diabetes. Losing weight if you are overweight, and increasing your levels of physical activity, can help to reduce insulin resistance and therefore make the insulin that is produced more effective at controlling your blood glucose levels.
If you have pre-diabetes, you should:
- Eat a healthy balanced diet. Your practice nurse and/or a dietician will give details on how to eat a healthy diet. The diet is the same as recommended for everyone. The idea that you need special foods if you have pre-diabetes or diabetes is a myth. Basically, you should aim to eat a diet low in sugar high in fibre, with plenty of fruit and vegetables:
- Starchy foods contain carbohydrates. Standard advice is that you should continue to eat some starchy foods, although you should focus on wholegrain and wholewheat versions - so-called 'complex carbohydrates'. These tend to have a lower glycaemic index (GI) which means they are more slowly absorbed and do not raise your blood sugar as rapidly.
- However, what many people don't realise is that starchy carbohydrates like bread, potatoes or breakfast cereals digest down into a surprisingly large amount of sugar. More and more people are discovering that by reducing the carbs (both sugary and starchy) in their diet, it is possible to lose weight and reduce blood sugar (glucose). If you do include carbs in your diet, choose complex carbs.
- See the separate leaflet called Type 2 Diabetes Diet for more details.
- Lose weight if you are overweight. Getting to a perfect weight is unrealistic for many people. However, if you are overweight or obese then losing some weight will help to reduce your blood glucose level (and have other health benefits too). See the separate leaflet called Weight Loss (Weight Reduction).
- Do some physical activity regularly. If you are able, a minimum of 30 minutes of physical activity at least five times a week is advised. For example, walking, swimming, cycling, jogging, dancing - anything that makes you at least mildly out of breath and mildly sweaty. You can start slowly and build up. You can also spread the activity over the day - for example, two 15-minute spells per day. Regular physical activity also reduces your risk of having a heart attack or stroke. Always check with your doctor that it is safe to start exercising if you have been inactive for a long period. See the separate leaflet called Exercise and Physical Activity. The most effective treatment is lifestyle changes, including eating a healthy balanced diet, losing weight if you are overweight, and doing regular physical activity.
Public Health England advises 150 minutes of physical activity each week, in bouts of 10 minutes or more. This might feel like a tall order, but it can be done in a way that becomes an enjoyable part of your life. Honestly.— Dr Mary Harding, The best forms of exercise for those who hate the gym
There are also other lifestyle changes that you can make to reduce your cardiovascular disease risk. These include:
- Stopping smoking if you are a smoker.
- Ensuring that you stick to the recommended alcohol intake. See the separate leaflet called Alcohol and Sensible Drinking for more details.
Make sure that your blood pressure stays within the normal range. Have your blood pressure checked regularly with your practice nurse.
Also, discuss with your doctor or practice nurse if you need a cholesterol check and/or treatment to lower your cholesterol level.
Treatments with medicines
A number of medical trials have looked at the use of various treatments with medicines for people with pre-diabetes to see if they can help to prevent diabetes and cardiovascular disease.
Medicines that have been trialled include:
- Angiotensin-converting enzyme (ACE) inhibitors.
- Angiotensin-II receptor antagonists (also known as angiotensin receptor blockers).
Lifestyle changes (as indicated above) are the most important thing if you are found to have pre-diabetes. However, the National Institute for Health and Care Excellence (NICE) has recommended that metformin should be used if a lifestyle-change programme isn't successful or isn't possible because of a disability or medical reasons. A medicine called orlistat may occasionally also be recommended to help lose weight and therefore reduce the risk of developing diabetes.
What follow-up is needed if you have pre-diabetes?
You will usually need a blood test to check your fasting blood sugar (glucose) level at least once a year.
This is to make sure that you have not developed diabetes. Your doctor is also likely to keep a check on any other risk factors that you may have for cardiovascular disease.
So, they may monitor your weight and your blood pressure and also suggest a blood test to check your cholesterol and triglyceride levels.
In the meantime, if you develop any symptoms of diabetes, you should visit your doctor sooner.
What are the complications of prediabetes?
The main complication of pre-diabetes is progression to type 2 diabetes.
Pre-diabetes also increases your risk of developing:
- Heart disease.
- Peripheral arterial disease.
- Stroke (cardiovascular diseases).
- High blood pressure.
- Raised cholesterol levels.
- Weight issues.
Can pre-diabetes be prevented?
The same things that can help in preventing type 2 diabetes can help prevent pre-diabetes (impaired glucose tolerance). These include:
- Eating a healthy balanced diet.
- Losing weight if you are overweight.
- Doing some physical activity regularly.
If you do develop type 2 diabetes, it's important to go for regular check-ups to ensure it doesn't worsen.
Further reading and references
Type 2 diabetes: prevention in people at high risk; NICE Public Health Guidance (last updated: September 2017)
Ford ES, Zhao G, Li C; Pre-diabetes and the risk for cardiovascular disease: a systematic review of the evidence. J Am Coll Cardiol. 2010 Mar 3055(13):1310-7.
Perreault L, Pan Q, Mather KJ, et al; Effect of regression from prediabetes to normal glucose regulation on long-term reduction in diabetes risk: results from the Diabetes Prevention Program Outcomes Study. Lancet. 2012 Jun 16379(9833):2243-51. doi: 10.1016/S0140-6736(12)60525-X. Epub 2012 Jun 9.
Type 2 Diabetes Know Your Risk; Diabetes UK
Weber MB, Hassan S, Quarells R, et al; Prevention of Type 2 Diabetes. Endocrinol Metab Clin North Am. 2021 Sep50(3):387-400. doi: 10.1016/j.ecl.2021.05.003. Epub 2021 Jul 12.