Back in 2013 (when this post was first published), it was quite fashionable to ‘quit sugar’.
Health and well-being messages have moved on in the past decade, but limiting refined sugar is still a wise choice.
Here in Australia, we’re reminded that eating a diet high in added sugar can lead to a person becoming overweight or obese, increasing the risk of type 2 diabetes and some cancers and stroke.
Diabetes is linked to poor brain health.
Diabetes, especially type 2 diabetes, is not the cause of dementia, rather, it is a risk factor for dementia.
Using language we’ve become used to hearing since the COVID pandemic: dementia is a comorbidity of type 2 diabetes.
To put the information into numbers: people with diabetes have a 1.4-2-fold increased risk for developing Alzheimer’s disease.
And if you have diabetes, you’re also at greater risk for general cognitive decline as you age.
Scientists are still unravelling the exact molecular pathways and mechanisms that link diabetes and dementia, but it’s most likely a combination of the effects of insulin resistance, vascular pathology, oxidative stress, glucocorticoid excess and inflammation.
Not too worried because you don’t have diabetes? Well, hold back on that chocolate…
You don’t need to have diabetes to be at risk of dementia.
Higher blood sugar levels are associated with higher dementia risk, even among people who do not have diabetes
A 2013 report in the New England Journal of Medicine followed 2000 over-65-year-olds for five years in the Adult Changes in Thought (ACT) study. The participant’s blood sugar levels were taken 17 times and averaged out over the course of the study.
The finding was clear: high blood sugar levels were associated with an increased risk of developing dementia.
In people WITH diabetes, dementia risk was 40% higher for people with an average glucose level of 190 mg/dl than those with an average glucose level of 160 mg/dl.
For people WITHOUT diabetes, those with an average glucose level of 115 mg/dl were compared to people with an average glucose level of 100 mg/dl (normal is 70-100 mg/dl). The higher blood sugar group had an 18% higher risk of developing dementia.
Associate Professor Paul K. Crane, one of the authors from the University Washington School of Medicine, said,
“What we found was that people with higher levels of glucose had a higher risk of dementia, on average, than did people with lower levels of glucose …
There was no threshold value for lower glucose values where risk levelled off.”
Paul K. Crane
Rather depressingly, the authors reported that they have not yet found evidence that dementia risk could be lowered even if people ate less sugar.
“Your body turns your food into glucose, so your blood sugar levels depend not only on what you eat but also on your individual metabolism: how your body handles your food…
While that is interesting and important, we have no data to suggest that people who make changes to lower their glucose improve their dementia risk.”
Paul K. Crane
It’s not all bad news.
Professor Crane and the ACT study group have previously found that exercise lowers the risk of dementia developing (as have numerous other studies).
It turns out exercise is one of the best ways to regulate your blood sugar levels and prevent the development of diabetes.
2023 Research Updates
New research published in 2022, has shown that brain ageing speeds up by 26% in people with type 2 diabetes. The most dramatic change occurs in parts of the brain critical for learning, decision making and other executive functions.
The relationship between glucose levels and Alzheimer’s disease is seen in adults as young as 35. In a 40-year study, elevated blood glucose levels in healthy people from age 35 onwards increased Alzheimer’s disease risk. Once study participants reached middle age, every 15 mg/dL increase in blood glucose caused a 14.5% increased risk of Alzheimer’s disease.
The people within the higher blood sugar group in this ACT study could also be labelled as having prediabetes. Further research has now shown that middle-aged people with prediabetes have a similar rate of cognitive decline as those with diabetes. Prediabetic people were also found to be 54% more likely to develop vascular dementia over an 8-year period than healthy individuals.
Experiencing a physically and cognitively active life can significantly reduce dementia risk, even if you don’t have diabetes. But interestingly, active older people with diabetes have a similar dementia risk to highly active individuals without diabetes. Meanwhile, inactive people with diabetes have a nearly 30% greater risk of dementia compared to diabetic people with active lifestyles. In short: staying active matters!
Important New Research
One interesting mechanism that likely links Alzheimer’s disease to diabetes is the accumulation of a protein called amyloid-beta. Build-ups of amyloid-beta within the brain are a known contributor to Alzheimer’s disease. This protein is also immediately released into the bloodstream in response to increased glucose and insulin by other organs, like the pancreas and liver.
The higher glucose and insulin levels in people with diabetes mean that the level of amyloid-beta in the blood is more consistently raised. Increases of this protein within the blood can prevent it from being removed from the brain at blood vessels. Increased insulin also prevents any excess amyloid-beta in the brain from being broken down and detoxified. This can all cause an accumulation of amyloid-beta in the brains of people with diabetes which could increase their risk of later developing Alzheimer’s disease.
Though controlling glucose with diet can be difficult, emerging research suggests that taking diabetes medications can protect against dementia. Unmedicated diabetic people develop Alzheimer’s disease six times faster than people who don’t have diabetes. Meanwhile, people who are medicated for their diabetes develop dementia at a similar rate to non-diabetic individuals.
The Sydney Memory and Ageing Study found older people who treat their type 2 diabetes with the anti-diabetic drug metformin experience slower cognitive decline and decreased rates of dementia.
However, the lead researcher of this study Professor Katherine Samaras believes that metformin may additionally protect non-diabetic people at greater risk of dementia:
“This study has provided promising initial evidence that metformin may protect against cognitive decline. The intriguing question is whether metformin is helpful in people in those with normal glucose metabolism. We are now planning a large, randomised controlled trial of metformin in individuals at risk of dementia and assess their cognitive function over three years. This may translate to us being able to repurpose this cheap medication with a robust safety profile to assist in preventing against cognitive decline in older people.”
Professor Katherine Samaras
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