Diabetes - its role in cognitive impairment and dementia

There was an alarming article recently in the Guardian newspaper. It said that in the UK, diabetes is now nearly four times as common as all forms of cancer combined. Some 3.6 million people in the UK are thought to have type 2 diabetes (2.8 are diagnosed, but there’s thought to be a large number undiagnosed) and nearly twice as many people are at high risk of developing it. The bit that really stunned me? Diabetes costs the health service roughly 10% of its entire budget. In north America, one in five men over 50 have diabetes. In some parts of the world, it’s said as much as a quarter of the population have diabetes or even a third (Nauru)! Type 2 diabetes is six times more common in people of South Asian descent, and three times in people of African and African-Caribbean origin.

Why am I talking about diabetes in a blog dedicated to memory and learning? Because diabetes, if left untreated, has a number of complications, several of which impinge on brain function.

For example, over half of those with type 2 diabetes will die of cardiovascular disease, and vascular risk factors not only increase your chances of heart problems and stroke (diabetes doubles your risk of stroke), but also of cognitive impairment and dementia.

Type 2 diabetes is associated with obesity, which can bring about high blood pressure and sleep apnea, both of which are cognitive risk factors.

Both diabetes and hypertension increases the chances of white-matter lesions in the brain (this was even evident in obese adolescents with diabetes), and the degree of white-matter lesions in the brain is related to the severity of age-related cognitive decline and increased risk of Alzheimer’s.

Mild cognitive impairment is more likely to develop into Alzheimer’s if vascular risk factors such as high blood pressure, diabetes, cerebrovascular disease and high cholesterol are present, especially if untreated. Indeed it has been suggested that Alzheimer’s memory loss could be due to a third form of diabetes. And Down syndrome, Alzheimer's, diabetes, and cardiovascular disease, have been shown to share a common disease mechanism.

So diabetes is part of a suite of factors that act on the heart and the brain.

But treatment of such risk factors (e.g. by using high blood pressure medicines, insulin, cholesterol-lowering drugs and diet control, giving up smoking or drinking) significantly reduces the risk of developing Alzheimer’s. Bariatric surgery has been found to improve cognition in obese patients. And several factors have been shown to make a significant difference as to whether a diabetic develops cognitive problems.

Older diabetics are more likely to develop cognitive problems if they:

  • have higher (though still normal) blood pressure,
  • have gait and balance problems,
  • report themselves to be in bad health regardless of actual problems (this may be related to stress and anxiety),
  • have higher levels of the stress hormone cortisol,
  • don’t manage their condition (poor glucose control),
  • have depression,
  • eat high-fat meals.

Glucose control / insulin sensitivity may be a crucial factor even for non-diabetics. A study involving non-diabetic middle-aged and elderly people found that those with impaired glucose tolerance (a pre-diabetic condition) had a smaller hippocampus and scored worse on tests for recent memory. And some evidence suggests that a link found between midlife obesity and increased risk of cognitive impairment and dementia in old age may have to do with poorer insulin sensitivity.

Exercise and dietary changes are of course the main lifestyle factors that can turn such glucose impairment around, and do wonders for diabetes too. In fact, a recent small study found that an extreme low-calorie diet (don’t try this without medical help!) normalized pre-breakfast blood sugar levels and pancreas activity within a week, and may even have permanently cured some diabetics after a couple of months.

Diabetes appears to affect two cognitive domains in particular: executive functioning and speed of processing.

You can read all the research reports on diabetes that I’ve made over the years in my new topic collection.

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