Medical professionals are advising people to be aware of the less obvious indicators of diabetes, which include blurred vision, recurring yeast infections, tingling sensations in the extremities, and even crusty skin areas in the armpits.

They caution that these signs are frequently mistaken for natural aging, putting individuals in jeopardy of serious health issues like vision loss, limb amputation, heart attacks, and strokes.

This warning is issued as a recent study, featured in The Lancet, reveals that nearly 25% of diabetes cases go undiagnosed in the UK—a particularly high rate by European standards. Researchers from the University of Washington in Seattle estimate that while about 4.6 million individuals in the UK are aware of their diabetes, roughly 1.5 million are unknowingly living with it.

Specialists note that the overwhelming majority of these cases are type 2 diabetes, which makes up 90% of diagnoses and is frequently associated with a lack of physical activity and an unhealthy diet.

Type 2 diabetes arises when the body either does not produce sufficient insulin or develops resistance to it. Insulin is the hormone responsible for controlling blood sugar, or glucose levels. In its absence, glucose can rise to dangerously high levels, causing damage to blood vessels and organs.

The other prevalent type, type 1 diabetes, is an autoimmune disorder where the body attacks its insulin-producing cells and is typically identified earlier in life.

‘The trouble for many patients with type 2 diabetes is that the symptoms come on slowly and become part of everyday life,’ says Professor Andrew Hattersley, a diabetes expert at the University of Exeter.

‘The other challenge is that the common symptoms are easy to ignore as something we all suffer from at one point in time.

‘However, early treatment is crucial for preventing complications and long-term consequences – for example, heart disease is twice as likely to occur in patients with unmanaged diabetes – so it is important that you see a doctor if you are concerned.’

For 47-year-old gardener Mark McGovern the clues were all there, but, he admits, he simply ignored them.

Waking in the night to go to the loo, feeling constantly tired, always sipping water and suffering pins and needles in his feet all seemed like part of getting older. ‘I was just being a typical bloke,’ says Mark. ‘I realised that these things had changed but I brushed them off – it didn’t feel like it could be anything serious.’

But in 2016, while driving to work, he suddenly began to see double.

Terrified, he pulled over and was taken to hospital, where doctors told him he had suffered a stroke caused by undiagnosed type 2 diabetes.

‘I was in shock when they told me,’ he recalls. ‘I had never even considered that those signs could have been diabetes – or that they could have such a serious impact on my life.’

Nearly a decade on, Mark is still living with the consequences. ‘I am a shell of the man I used to be,’ he admits. ‘I have lost my job because I can no longer operate the machines, and I can suffer mini strokes three times a week, which has led me to become a hermit and stay indoors.’

Left untreated, fluctuating blood sugar can lead to a range of long-term complications: permanent eye problems, nerve damage that causes pain or numbness, kidney failure, heart disease and, in the most serious cases, limb amputations.

In 2013 actor Tom Hanks revealed he had type 2 diabetes, which he blamed on his ‘lazy American diet’ and unhealthy eating in childhood.

A 2022 study published in the BMJ found failing to diagnose and manage diabetes raises the risk of dying from any cause by 13 per cent.

Doctors often advise looking out for the ‘four Ts’: thirst, thinner, tired and toilet – meaning excessive thirst, unexplained weight loss, fatigue and frequent urination. But experts warn there are many subtler red flags, and one of the most overlooked is changes in eyesight.

‘If patients are experiencing fluctuations in their vision throughout the day – for example, periods of blurriness around mealtimes – this may be a sign of diabetes and they should get tested,’ says Dr Louise Gow, head of optometry and low vision at the Royal National Institute of Blind People. ‘One of the tell-tale signs is if people come back complaining their prescription for their glasses is suddenly wrong soon after being seen – then it may be that diabetes is causing the fluctuations.’

She adds: ‘It is so upsetting to see patients who have lost their eyesight from something completely preventable. Changes in vision are a common sign of diabetes that people really need to be aware of.’

Recurrent infections are another giveaway. High sugar levels create the perfect breeding ground for yeast and bacteria.

‘If a patient, particularly women, are suffering from three or more episodes of thrush in a year, then they should get their blood sugar checked,’ says Dr David Strain, an expert in cardiometabolic health at the University of Exeter medical school.

Other subtle signs include slow-healing cuts, tingling or numbness in the hands and feet – caused by nerve damage from raised sugar – and crusty, brownish patches of skin, especially in the armpits or on the neck.

Known medically as acanthosis nigricans, these patches develop when high levels of insulin in the blood stimulate skin cells to multiply more rapidly, creating areas that are darker, thicker and sometimes slightly rough or velvety to the touch. They are not harmful, but are a visible marker of insulin resistance – the stage before diabetes when the body struggles to use insulin effectively.

To the untrained eye, they can easily be mistaken for eczema, a persistent rash, or even dirt that won’t wash off.

‘These are incredibly common, particularly in black and Asian people,’ says Dr Strain. ‘While these patches are usually harmless, if they appear alongside other symptoms, it is a red flag.’

He adds: ‘Catching diabetes early is key to preventing complications.

‘Even a brief period of undiagnosed diabetes, like a year or two, can have long-term consequences on the body. The impact of high blood sugar during this time can last seven years, raising the risk of heart attacks or strokes even once it is being treated.’

In some people, however, there can be few, if any, symptoms at all. College tutor Ken Heard, 64, is a case in point. ‘One of the only symptoms I had was dehydration – I would always be sipping a glass of water on my desk,’ he says. ‘Then I was always having to go to the toilet, but I thought that was just because I was healthy and drinking lots of water.’

It was only by chance that he spotted a poster at a pharmacy offering diabetes checks, listing the very symptoms he was experiencing. He took the test – and discovered he had type 2 diabetes.

‘I had a healthy BMI, so having diabetes never even crossed my mind,’ he says. ‘However my dad had it, and I now know that is a factor as well.

‘I feel incredibly lucky it was caught when it was, as I hadn’t developed any serious complications – and who knows how long I would have gone on for.’

Ken’s experience underlines why the NHS now offers free health checks, via GP services, to everyone aged 40 and over. These are designed to pick up early warning signs of conditions such as high blood pressure, heart disease and type 2 diabetes.

Once diagnosed, type 2 diabetes can often be managed and complications avoided. Doctors urge patients to shed excess weight, eat a diet rich in vegetables and whole grains, and exercise regularly. Even a brisk daily walk makes a difference.

Research shows losing just 5 to 10 per cent of body weight can dramatically improve blood sugar control, and in some cases even put the condition into remission.

If lifestyle changes aren’t enough, tablets such as metformin are typically prescribed to help the body use insulin more effectively. Over time, other drugs may be required to boost insulin production or inhibitors used to slow down sugar absorption.

In more advanced cases, daily insulin injections may be needed. Patients are also monitored closely with blood tests, eye checks and foot exams to catch complications early.

Experts say patients who suspect diabetes should ask for a specific diagnostic test.

Known as the HbA1c blood test, it measures average blood sugar levels over the past two to three months, rather than at a single moment in time.

It does this by looking at haemoglobin – the protein in red blood cells that carries oxygen. Sugar sticks to haemoglobin molecules, and the more sugar in the blood the more that becomes glycated.

Because red blood cells live for around three months, the test provides a reliable long-term picture of blood sugar control.

‘If patients are concerned then they should ask their GP for this test,’ says Professor Hattersley. ‘Especially if they are younger, as it may not necessarily be considered.’

Experts fear that younger people are the most likely to be suffering from undiagnosed diabetes.

The Lancet study found people under 35 were least likely to be diagnosed – with just one in five aware they had the condition.

‘There are a few reasons why this is the case,’ says Professor Hattersley. ‘Young people are less likely to go to the doctor regularly, but also there is still a perception that this is a disease that affects old people, so often GPs fail to request the necessary test to ensure a timely diagnosis.’

Commenting on the research, Nikki Joule, policy manager at Diabetes UK, said: ‘Despite improvements over the past 20 years, underdiagnosis of type 2 diabetes remains a major challenge in the UK, particularly in young people.

‘With one in five adults now living with diabetes or prediabetes in the UK, this research shows there is still a long way to go in improving diagnosis and treatment.’

Even marathon men run risk of getting diabetes 

Veteran marathon runner Tony Pidgeon, right, was shocked to be diagnosed with type 2 diabetes.

The father-of-two, 57, was a healthy weight and had no symptoms when it was revealed by a routine blood test in 2021.

‘For me it was a completely hidden disease, with no signs or symptoms,’ says Tony from Oxfordshire, pictured right, who has completed 18 marathons around the world.

‘Years earlier I had been told I was prediabetic, but I had been eating well and was extremely active so I never thought I would tip into the diabetic zone.’

He did, however, have a family history of type 2 diabetes, with his grandfather and mother also having suffered with it. Following his diagnosis he took part in a research trial run by the University of Oxford that looked into whether a low-calorie and low-carbohydrate diet can lead to remission for type 2. The study involves participants maintaining a low-carbohydrate diet of 800 to 1,000 calories a day for three months.

‘The diet was brutal, but it has allowed me to control my blood sugar levels,’ says Tony.

‘And when I start to put weight back on I have been taught the skills to manage my condition.’