The latest figures are all too clear: we are in the middle of an epidemic of diabetes.

The chronic condition, driven by obesity and persistently high blood sugar levels, now affects 4.6 million people in the UK – a record high, according to the charity Diabetes UK.

It's a deadly illness which costs the NHS £10 billion a year to treat, causing damage to organs, nerves and cells, and dramatically increases the risk of heart disease, kidney disease, amputations and sight loss.

This means, understandably, there has been a drive to diagnose people at risk – with the ambitious aim to slow down or even prevent the slide towards full-blown diabetes.

In recent years, doctors have warned patients with elevated blood sugar that they are at a higher risk of a type 2 diabetes diagnosis, the most common form of the condition triggered by poor diet and lifestyle. 

In some cases patients are told they have prediabetes. This affects 6.3 million people – nearly one in eight adults in England – and typically has no symptoms.

The UK has invested in a Diabetes Prevention Programme (DPP) which encourages those diagnosed with prediabetes to lose weight and reduce their blood sugar readings.

About 1.7 million people have been referred to the DPP since it was launched in 2018, but not everyone agrees these cases should be identified.

In fact, the man who coined the term 'prediabetes' in 2001 recently claimed that doing so was 'a big mistake'.

Dr Richard Kahn, former chief scientific adviser to the American Diabetes Association, now says diagnosing and treating prediabetes causes unnecessary anxiety and only serves to line the pockets of drugs companies. 

He adds that millions spent on government programmes focused on weight loss and exercise have been a 'terrible waste of money' with lacklustre results.

It's quite the U-turn, given that last week the chief executive of Diabetes UK, Colette Marshall, called for more cases of prediabetes and type 2 diabetes to be diagnosed. 'The sooner we can find and get them the care they need, the more harm we can prevent,' she said.

Last week, when The Mail on Sunday's resident GP, Dr Ellie Cannon, asked readers whether being diagnosed with prediabetes had been helpful, the responses were mixed.

Some said the knowledge had 'saved' them – while others diagnosed in their 80s said it had left them 'frightened to death' about what they could eat.

One reader, Reverend Lynne Morris, 71, from Telford, Shropshire, said she dropped four dress sizes after changing her diet when her prediabetes was diagnosed. 'I'm convinced that without that initial prediabetes diagnosis, and consequent diet change, I would certainly be a type 2 now,' she wrote.

Su Watts, 76, from South Gloucestershire, also turned her health around after being offered a place on the DPP last year.

Referring to Dr Kahn, she said: 'I am no longer prediabetic, so where's the mistake?' But others were more sceptical. 

Lina Tan, 69, from Hampshire, said she was slim, active and a vegetarian when she was diagnosed, and added: 'How much more can I improve on my lifestyle and diet?'

And an 80-year-old from Bedfordshire, who received an 'alarming' text from her GP saying she was prediabetic, said: 'This initiative must mean extra work for already time-strapped GPs and surgery staff, with all the 'prediabetics' calling in response to texts urging them to book blood tests.'

So, what's the truth about prediabetes – and are you better off not knowing your risk?

UK experts say Dr Kahn's comments don't reflect the huge gains made to the nation's health by intervening early.

Kamlesh Khunti, professor of primary care diabetes and vascular medicine at the University of Leicester, said: 'There is overwhelming evidence that we can prevent diabetes in high-risk individuals.

'Some longer-term studies have shown reductions in strokes, deaths from heart disease and eye complications which can cause blindness.'

It's important to note the differences between the UK and the USA when it comes to diagnosing and treating prediabetes, which means some of what Dr Kahn suggests may not apply here.

The US has a broader definition of what counts as prediabetes, so more people – and many who'd be considered healthy in the UK – fall into the bracket.

The UK uses the the same criteria as the World Health Organisation, which classes it as an HbA1c reading of between 42mmol/mol and 47mmol/mol. 

This is an average measurement of the amount of glucose, a type of sugar, in the blood over the previous two to three months. In the US it is between 39 and 47mmol/mol (although doctors there prefer to assess blood sugar in milligrams per deciliter (mg/dl) which measures the weight of the glucose in the blood).

Professor Naveed Sattar, an expert in diabetes at the University of Glasgow, says: 'The definition in the US is too broad – ours gives a better idea of who is actually at risk.'

This is borne out in statistics which indicate how many people with prediabetes go on to develop type 2. In countries which use the WHO's criteria it's about 24 per cent. In the US, it's 14 per cent – so more people are being treated when they don't need to be, or who may never develop the disease.

However, experts say its important that patients are informed that a prediabetes diagnosis does not mean they will go on to develop diabetes.

Dr Chirag Bakhai, NHS England's national clinical adviser for diabetes, says: 'The term prediabetes can suggest developing type 2 diabetes is inevitable, when that isn't the case. Some people with slightly raised sugar levels, but below the diabetes range, find these stay steady or revert to normal on their own.'

Some studies found blood sugar levels can rise naturally with age.

In fact, a US review found older adults (aged between 71 and 90) with prediabetes were much less likely to progress to type 2 than younger adults.

One of the study authors, Elizabeth Selvin, at Johns Hopkins Bloomberg School of Public Health, said the results suggested prediabetes 'is just not a robust diagnosis' for older adults.

For this reason, some experts argue that many older adults should only be told of their risk if they are in immediate danger of developing diabetes.

Another difference between the UK and the US is the use of medicines to treat prediabetes. In the US, prediabetes are given drugs, including even weight-loss jabs such as Ozempic.

But, in the UK, the vast majority of these patients receive only lifestyle and diet advice. Some patients on the cusp of diabetes may receive the blood sugar-lowering drug metformin.

However, experts say that, since metformin tablets cost pennies, drug companies do not make vast profits from NHS prediabetes diagnoses, unlike in the US.

But what of Dr Kahn's other claim, made six years ago, that there is no good evidence that intervention programmes work in the longer term?

One study from China, which followed participants for 30 years, showed that lifestyle changes delayed the onset of diabetes by an average of nearly four years.

This might not sound like much, but even that was enough to cause 26 per cent fewer heart problems and 35 per cent fewer additional complications such as blindness. 

It also reduced deaths from all causes by 26 per cent, and boosted average life expectancy by an average of one-and-a- half years.

However, in the UK, experts say one major problem is that many prediabetes patients do not stick with the NHS advice they receive.

In the UK, anyone with prediabetes over the age of 18 can be referred to

the DPP by their GP, which involves nine months of personalised support to eat healthy, exercise, improve sleeping habits and lose weight.

An analysis in 2022 found those completing the course reduced their risk of type 2 by 37 per cent after two years – a substantial reduction on the clinical trial results. But most people don't complete the course.

In fact, of the 1.8 million referred to the DPP, just 840,000 – 46 per cent – have actually taken part. And even fewer finish it.

Despite this, many experts argue that a prediabetes diagnosis can help patients avoid diabetes – and even save them from other life-threatening conditions.

'Early analyses show an association between completing the programme and reducing the risk of other long-term conditions, such as cardiovascular disease,' says Dr Chirag Bakhai.

'Even if you can just delay the onset by a couple of years, you'll still be delaying the damage it can cause, which will likely have a benefit to your health in the longer term.'