Drinking less alcohol and reducing the risk of type 2 diabetes are strong factors in helping people cut their chances of dementia, research suggests.
Limiting exposure to traffic-related air pollution could also reduce the risk of developing the condition, according to the study.
It has been suggested that the findings could also help explain why certain groups may be more vulnerable to dementia.
The scientists have previously identified a weak spot in the brain which is a specific area that develops later during adolescence, and also shows earlier degeneration in old age.
In the new study, 161 risk factors for dementia were examined, and ranked according to their impact on this brain network, over and above the natural effects of age.
The University of Oxford researchers classified these so-called modifiable risk factors – as they can potentially be altered throughout life to reduce the risk of dementia – into 15 broad categories.
These were blood pressure, cholesterol, diabetes, weight, alcohol consumption, smoking, depressive mood, inflammation, pollution, hearing, sleep, socialisation, diet, physical activity, and education.
The findings suggest that when it comes to risk factors that people can do something about, alcohol intake, diabetes and traffic-related air pollution are the most harmful.
According to Diabetes UK, the main things someone can do to lower their chance of developing type 2 diabetes is to eat more healthily, lose weight if needed so they have a healthy weight and healthy waist size and to move more.
The researchers investigated the genetic and modifiable influences on these brain regions by looking at the brain scans of 40,000 people in the UK Biobank database aged over 45.
Professor Gwenaelle Douaud, who led the study, said: “We know that a constellation of brain regions degenerates earlier in ageing, and in this new study we have shown that these specific parts of the brain are most vulnerable to diabetes, traffic-related air pollution – increasingly a major player in dementia – and alcohol, of all the common risk factors for dementia.
“We have found that several variations in the genome influence this brain network, and they are implicated in cardiovascular deaths, schizophrenia, Alzheimer’s and Parkinson’s diseases, as well as with the two antigens of a little-known blood group, the elusive XG antigen system, which was an entirely new and unexpected finding.”
The XG blood group system is a classification of blood based on the presence of proteins called Xg antigens – substances capable of stimulating an immune response – on the surfaces of red blood cells.
It is the only blood group system located on the X chromosome.
The researchers suggest it has been largely neglected, and while its main contribution related to the mapping of the X chromosome itself, its clinical role remains elusive.
The study analysed the unique contribution of each controllable risk factor by looking at all of them together to assess the resulting degeneration of this particular brain weak spot.
Professor Anderson Winkler, a co-author from the National Institutes of Health and the University of Texas Rio Grande Valley in the US, said: “It is with this kind of comprehensive, holistic approach – and once we had taken into account the effects of age and sex – that three emerged as the most harmful: diabetes, air pollution, and alcohol.”
Dr Susan Mitchell, head of policy at Alzheimer’s Research UK, said: “With no treatments yet available in the UK that can stop or slow the diseases that cause dementia, there has never been a more pressing need to promote good brain health and to gain a deeper understanding on how dementia can be prevented.
“It’s generally accepted that up to 40% of dementia cases are potentially preventable, so there is an enormous opportunity to reduce the personal and societal impact of dementia.
“These intriguing findings, based on retrospective analysis of brain scans and other data from 40,000 people who took part in the UK Biobank project, help shed light on this further.
“The results will need confirming, both in forward-looking studies that follow participants over time, and in a more diverse study population.
“But they could help explain why certain groups may be more vulnerable to dementia – such as those living in highly polluted areas.
“As we head towards a general election, we want all political parties to acknowledge the concept and importance of brain health, and make commitments that will address these drivers of dementia risk across the UK.”
The study is published in Nature Communications.