Not for nothing has type 2 diabetes been dubbed ‘a 21st Century epidemic’. Year after year, numbers continue to spiral upward. At the last count, one in ten Britons over 40 are living with a diagnosis – and this condition eats up a tenth of the annual £134billion NHS budget.
And, over the past decade, studies have revealed something even more alarming: scientists believe that the cascade of deadly problems which lead to type 2 diabetes – caused by too much body fat – may also lead to Alzheimer’s disease.
So strong are the associations between the two illnesses that some describe the incurable brain disease as ‘type 3 diabetes’.
One study of people with Alzheimer’s found 81 per cent had either diabetes or raised blood sugar levels, known as prediabetes, which puts them on the cusp of developing the full-blown condition.
Sophia Husbands, whose mother Caroline developed type 2 diabetes in her late 50s and now, just a few decades on, aged 75, has symptoms which point to dementia
But, shocking as this new twist is, it also offers a potentially game-changing opportunity to prevent the brain disease for the first time – by tackling type 2 diabetes early. And it opens the door to potential new treatments for dementia, too. Studies have found cheap diabetes drugs could be used for Alzheimer’s, and may even slow the progress of disease.
The science is still in its early stages, but it could be revolutionary because of the huge numbers it may benefit. At present, Alzheimer’s drugs only manage symptoms, and in a limited way slightly slow disease progression.
But researchers now think of dementia as part of the spectrum of illnesses linked to metabolic disease – an umbrella term often used to describe the triad of heart disease, high blood pressure and type 2 diabetes, which commonly occur together and are inextricably linked, each exacerbating the other.
That means, suddenly, there may be a more obvious way to prevent and treat it. And it could be as easy as losing weight and eating healthily.
‘Thinking about dementia as a metabolic disease shows a clear way forward,’ says Dr Ivan Koychev, senior clinical researcher in dementia at the University of Oxford. ‘While the term type 3 diabetes is a bit simplistic, there’s little doubt conditions such as diabetes make the dementia process worse.’
Dr Koychev is clear we can all take steps to mitigate this risk, and it is vital to think ahead. ‘Given the whole dementia process starts ten to 15 years before the first symptoms emerge, we need to start controlling these factors in middle age,’ he says.
Family heartbreak: Sophia's parents Caroline, centre, and Wilson, who died with Alzheimer's 14 years ago, far right. ‘It was very hard – we were very close’, said Sophia
‘Prevent diabetes and metabolic disease and you might also prevent dementia.’
As Stephen Wharton, professor of neuropathology at Sheffield University, puts it: ‘So far we’ve focused on finding a cure for dementia, which is great. But another way of looking at it is to say, “Don’t have heart disease, high blood pressure, and diabetes. Instead, control your weight, don’t smoke and have a good diet.”’
The mechanism linking vascular dementia, a less common form of the disease that occurs due to problems with blood flow to the brain, and metabolic disease, including diabetes, is well established. High blood pressure, which often features with these conditions, places more force on the artery walls, making them stiff.
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This makes it hard for oxygen-rich blood to flow freely through the small blood vessels into the brain. If brain cells receive fewer essential nutrients, they eventually die off, causing problems with memory and normal thinking. Blockages can also trigger mini-strokes, causing further damage.
The link between diabetes and Alzheimer’s, however, was found by studying brain cells. To understand this, it’s important to understand how type 2 diabetes works.
In those who suffer from the condition, it’s believed that weight gain and inactivity leads to fat accumulating in the liver and pancreas. This, in turn, affects production of the hormone insulin.
Normally, when we eat foods containing carbohydrates, they’re broken down into single molecules of sugar – usually glucose – during digestion and these molecules are absorbed into the blood.
At the same time, insulin is released by the pancreas, and the hormone helps move glucose from the blood and into cells, where it’s used for energy. But fat in the liver blocks the signalling that leads to the release of insulin and, without sufficient insulin, the body’s cells can’t take up glucose.
This leads to dangerously high levels of sugar in the blood, which over time causes damage to the heart and other organs.
The body pumps out more insulin from the pancreas to compensate, and this can also cause damage.
So strong are the associations between type 2 diabetes and Alzheimer's disease that some describe the incurable brain disease as ‘type 3 diabetes’ (file photo)
In people with Alzheimer’s, tests showed their brain cells were resistant to insulin. In the brain, if the cells can’t take up glucose they can’t communicate properly and die – which leads directly to problems with memory and thinking.
But excess insulin, as is found in those with type 2 diabetes, may also reduce the amount of an enzyme in the brain responsible for controlling a substance called amyloid in the body. Amyloid can flow naturally through the body. But less of the enzyme means more amyloid accumulates, causing it to become sticky and form clumps. In the brain, these clumps, known as plaques, interfere with brain function and ultimately, scientists believe, lead to irreversible damage and Alzheimer’s.
‘If you mess around with your body’s insulin levels, which is what happens with type 2 diabetes, you could be influencing the ability of the brain to clear amyloid,’ says Professor Tara Spires-Jones, of the UK Dementia Research Institute at The University of Edinburgh.
Specialist scanning techniques show that even before symptoms of dementia appear, those with type 2 diabetes already have insulin resistance in their brain cells.
Sophia Husbands’ mum Caroline developed type 2 diabetes in her late 50s.
‘She said to us, firmly, “This stops here,” ’ Sophia recalls. ‘She’d watched her mum, Janey, suffer a stroke after living with type 2 diabetes and high blood pressure.’
Caroline had taken her diabetes diagnosis seriously. She had gained weight after having children but she transformed her diet, cutting back on salt and baking instead of frying. She was adamant her children shouldn’t suffer the same fate.
But now, just a few decades on, Caroline, 75, has symptoms which point to dementia. She is set to have tests. It is all the