Ask the expert: what is prediabetes?

Around one in 10 people aged over 40 in the UK have type 2 diabetes. This occurs when the body can’t produce enough of the hormone insulin or the body’s cells don’t respond effectively to the insulin, which results in high blood sugar levels. 

Similar to type 2 diabetes, in prediabetes your blood glucose levels can be above normal values due to the issues related to the reduced action of insulin, which is called insulin resistance. 

However, the raised blood sugar levels in prediabetes aren’t high enough to meet the threshold for type 2 diabetes. Left untreated, prediabetes will develop into type 2 diabetes. 

Who is at risk of prediabetes?

There are two major risk factors for prediabetes: our genetics and our lifestyle. 

If you have a family history of prediabetes and/or type 2 diabetes, you are more at risk. People of South Asian, Afro-Caribbean and Black African descent also have a higher genetic risk of developing the condition. 

Your risk is also raised if you lead a sedentary lifestyle, smoke, drink excessive amounts of alcohol, follow an unhealthy diet and/or are overweight or obese. 

Women with polycystic ovary syndrome (PCOS) also have a higher risk of prediabetes. 

What are the symptoms of prediabetes?

Unfortunately, prediabetes doesn’t usually cause obvious or sudden symptoms. As with type 2 diabetes, it gradually develops over time and often early symptoms only become clear with hindsight after a later diagnosis. 

For example, you may feel very tired after a large meal as your body is struggling to cope with the amount of sugar (glucose) released into your bloodstream or you may generally feel fatigued through the day. 

You may develop darkly pigmented bands around your neck and underarms called acanthosis nigricans. These are clues that your body is trying to keep diabetes at bay by significantly increasing insulin production. 

Candidiasis (ie infection with the fungus candida) can also be a sign that your blood sugar levels are too high. 

If you’re concerned that you’re at risk of prediabetes, it is important to see your GP, who can arrange for you to have a blood test to check whether you have prediabetes. 

How is prediabetes diagnosed?

There are several different blood tests that can be used to test for diabetes and/or prediabetes. However, for prediabetes, the blood test most commonly used is the HbA1c test. 

HbA1c refers to glycated haemoglobin. Haemoglobin is a protein found in our red blood cells; glycated haemoglobin refers to haemoglobin to which blood sugars are attached. This occurs when our blood sugar levels stay raised for too long, allowing them to attach to haemoglobin over time. 

The HbA1c test is, therefore, used as a measure of how high our blood sugar levels have been over the last three months (that is, roughly the lifespan of our red blood cells). If you have prediabetes, a HbA1c test result will be between 42 to 47 mmol/mol; a result of 48 mmol/mol or higher means you have diabetes. 

The other tests that are used sometimes include testing for fasting blood glucose, two hours after a meal. Results in the range of 5.6mmol/l to 6.9mmol/l when fasting and 7.8mmol/l to 11.0mmol/l two hours after a meal are indicative of a defect in your body's ability to manage glucose. 

How is prediabetes treated?

Treatment for prediabetes involves lifestyle changes, rather than medication. The approach is two-fold, that is, treatment to reduce how much glucose you consume and increase how much energy you expend. 

Practically, this means changing your diet to reduce the amount of sugar and carbohydrates you eat, as well as increasing your activity levels. Together, this will help you lose any excess weight and maintain a healthy weight. 

Medication is needed if your prediabetes develops into diabetes. However, it is not inevitable that prediabetes will develop into diabetes — prediabetes is reversible if you take steps to change your lifestyle and stay motivated to maintain these positive changes. 

What are the complications of prediabetes? 

Prediabetes is a warning sign that you are at high risk of developing diabetes, which increases your risk of a host of other diseases, such as heart disease, kidney disease, diabetic retinopathy and peripheral nerve problems. Prediabetes itself can also damage your cardiovascular system, kidneys and eyes.  

Prediabetes can make it harder for you to lose weight and in women, can lead to changes in the menstrual cycle. 

How can prediabetes be prevented?

If you have a family history of diabetes or prediabetes or have acanthosis (a clinical sign of increased skin pigmentation), you can take steps to prevent the onset of prediabetes. 

This involves making the same lifestyle changes that are needed to prevent prediabetes from developing into type 2 diabetes, namely following a healthy, balanced diet low in sugar and carbohydrates, and exercising regularly.