Insulin resistance, which is more common in overweight people, is linked to an increased rate of cognitive decline, according to research by Israel’s Sackler School of Medicine.
Insulin resistance prevents muscle, fat, and liver cells from easily absorbing glucose. As a result, the body requires higher levels of insulin to function normally.
Without sufficient insulin, excess glucose builds up in the bloodstream, which can lead to diabetes and other serious conditions.
The study, published in the Journal of Alzheimer’s Disease, followed 500 patients with cardiovascular disease over 20 years.
The researchers assessed their baseline insulin resistance using the homeostasis model assessment (HOMA), then tested cognitive function with computerised tests that examined memory, executive function, visual spatial processing and attention.
Follow-up assessments were conducted 15 years after the start of the study and then again five years after that.
The researchers found that, having adjusted for external factors, participants who placed in the top quarter of the HOMA index were at an increased risk of poor cognitive performance and accelerated cognitive decline compared to those in the remaining three-quarters of the index.
The study’s lead author, Professor David Tanne, said: ‘These are exciting findings because they may help to identify a group of individuals at increased risk of cognitive decline and dementia in older age.
‘We know that insulin resistance can be prevented and treated by lifestyle changes and certain insulin-sensitising drugs. Exercising, maintaining a balanced and healthy diet, and watching your weight will help you prevent insulin resistance and, as a result, protect your brain as you get older.
‘This study lends support for more research to test the cognitive benefits of interventions such as exercise, diet, and medications that improve insulin resistance in order to prevent dementia.’
This was a retrospective cohort study, helpful for delineating the natural history of a disease and its risk factors.
Accumulating evidence suggests a major role for chronically raised high blood sugar levels (typically seen in both diabetes and pre-diabetes) and the development of cognitive decline.
These diseases may develop as a result of chronic inflammation. Both high blood sugar (hyperglycaemia) and insulin resistance are implicated in causing inflammation in blood vessels which damages both those vessels and the organs/systems supplied by those vessels.
Multiple studies have suggested there may be a link between increased rates of Alzheimer’s and increased levels of obesity and type-2 diabetes. Both are associated with insulin resistance. It is still too early to state that one causes the other.
This paper looked at 489 patients with coronary artery disease who were already part of a major trial looking at the effect of a cholesterol-lowering agent on cardiovascular health and mortality. This is significant, as those with coronary artery disease invariably have evidence of vascular disease elsewhere in the body; inflammation in the vessels is part of the disease process.
Patients were followed up after the trial, assessed on average 15 years after inclusion and a further five years after that, giving ample time for the development of any cognitive decline. The initial 489 patients dropped to 347 at the second evaluation. The majority of study subjects were men.
After statistical adjustment, it was found that insulin resistance was associated with poorer overall mental performance, memory and function, even after people with diabetes were excluded from consideration. This is not a surprise as it is known that disruption of insulin activity in the brain leads to various deleterious changes, including impaired nerve cell function.
This study, like all, has its limits. The results may not be generalisable to women given that 95 per cent of the subjects were men and it is possible that the presence of other risk factors for cardiovascular disease may have confounded the results.
However, there is growing evidence that improving insulin sensitivity in non-diabetic individuals — via weight loss, exercise and potentially the use of medication — may be one method of reducing the risk of Alzheimer’s and other forms of dementia. It certainly can do no harm.
In diabetic patients, though, the picture will be more complex, given the differences between insulin dependent and independent forms. Either way, evidence suggests that optimally controlling blood sugar may be of significant benefit in reducing the risk of dementia.
Take-home message: avoiding hyperglycaemia and insulin resistance by regular exercise, reducing consumption of processed carbohydrates and maintaining a healthy weight and body fat percentage may aid in reducing the risk of Alzheimer’s and other kinds of dementia.
Research score: 3/5