Keeping blood glucose levels in the low-normal range is reflected by a low glycosylated haemoglobin (HbA1C). A low HbA1c is usually a proxy for improved insulin sensitivity, which is associated with reduced risk for dementia in several studies. Type 2 diabetes, the net result of losing blood sugar control, almost doubles risk for dementia. Diabetes is also associated with more rapid brain shrinkage. Even people in the upper normal range of blood glucose have increased brain atrophy, impaired cognition and increased risk of dementia. 

One research trial measured HbA1c and glucose levels in several thousand elderly people over the course of almost seven years. In that time, slightly more than a quarter of the participants developed dementia, and the bottom line was that rising glucose levels were associated with increased risk of developing the condition, irrespective of whether the participants also had diabetes. Non-diabetics who experienced a modest increase in blood sugar levels had an 18 per cent increased risk of dementia, whereas those who already had diabetes at the start of the study or developed it within the trial period had a 40 per cent increased risk.

Of higher important that the of glucose control is the loss of insulin control. Back in 2004, researchers at Columbia University stated that people with high insulin levels – the principal hallmark of metabolic dysfunction – were twice as likely to develop dementia as those with healthy levels. Moreover, those with the highest insulin levels had the worst memories. The same year, an Italian study also established a link between heightened insulin levels and declining mental function.. Similarly, a Puerto Rican study found that people who consumed the large amounts of sugar doubled their risk of suffering poor cognitive function, whilst another US study discovered a strong correlation between blood sugar level and memory loss. Two studies – one in Ireland and the other in the United States –established a link between high dietary glycemic load (GL) and cognitive decline. Indeed, both of these reports suggested that high GL is even more predictive of the pathological changes associated with Alzheimer’s than either high carb or high sugar intake. A high GL diet is also associated with more amyloid plaque and cognitive decline, especially in those with the ApoE4 gene. A long-term study found evidence that this sort of shrinkage is more common among people with high blood glucose levels, even when those levels are still within what are considered ‘normal’ (i.e. non-diabetic) limits. This cognitive decline starts young. Cognitive decline in overweight children is associated with a high GL diet and adolescents with metabolic dysfunction driven by a high GL diet have been shown to have shrinkage of the hippocampal area of the brain, as well as other structural changes and cognitive deficits .

Practical Steps for Reducing Risk of Cognitive Decline

In practical terms this means:

avoiding sugar as much as possible, and consume wholegrains because the fibre in these foods helps ‘slow release’ the sugars.
Eating white bread is associated with a poorer cognitive test performance, whereas high fibre bread is associated with better performance, so always choose wholegrain varieties of bread and pasta .
Eating carbohydrate foods with protein, for example brown rice with fish, or porridge oats with seeds, or fruit with nuts, as this helps to reduce the glycaemic load (GL) of a meal.
Choose fruits that are low GL, such as berries, cherries and plums and consume grapes, raisins and bananas sparingly, as these are high GL.
Aim to base your meals and snacks around a wide array of vegetables and fruits, lean meats, oily fish, wholegrains, nuts, seeds, beans and pulses. A study in Finland and Sweden compared those with a healthy versus unhealthy diet, including the above criteria, in mid-life for future risk of developing Alzheimer’s disease and dementia 14 years later. Results showed that those who had the healthiest diets had an 88% decreased risk of developing dementia, and a 92% reduced risk of developing Alzheimer’s disease specifically.