One in three cases of Alzheimer’s disease worldwide is preventable, according to research from the University of Cambridge.
The main risk factors for the disease are a lack of exercise, smoking, depression and poor education, it says.
Previous research from 2011 put the estimate at one in two cases, but this new study takes into account overlapping risk factors.
Alzheimer’s Research UK said age was still the biggest risk factor.
Writing in The Lancet Neurology, the Cambridge team analysed population-based data to work out the main seven risk factors for Alzheimer’s disease.
- Mid-life hypertension
- Mid-life obesity
- Physical inactivity
- Low educational attainment
They worked out that a third of Alzheimer’s cases could be linked to lifestyle factors that could be modified, such as lack of exercise and smoking.
The researchers then looked at how reducing these factors could affect the number of future Alzheimer’s cases.
Simply tackling physical inactivity, for example, will reduce levels of obesity, hypertension and diabetes, and prevent some people from developing dementia”
Prof Carol BrayneUniversity of Cambridge
They found that by reducing each risk factor by 10%, nearly nine million cases of the disease could be prevented by 2050.
In the UK, a 10% reduction in risk factors would reduce cases by 8.8%, or 200,000, by 2050, they calculated.
Current estimates suggest that more than 106 million people worldwide will be living with Alzheimer’s by 2050 – more than three times the number affected in 2010.
Healthier old age
Prof Carol Brayne, from the Institute of Public Health at the University of Cambridge, said: “Although there is no single way to treat dementia, we may be able to take steps to reduce our risk of developing dementia at older ages.
“We know what many of these factors are, and that they are often linked.
“Simply tackling physical inactivity, for example, will reduce levels of obesity, hypertension and diabetes, and prevent some people from developing dementia.
“As well as being healthier in old age in general, it’s a win-win situation.”
Dr Simon Ridley, head of research at charity Alzheimer’s Research UK, said there was still much to discover about the disease.
“While age is the biggest risk factor for most cases of Alzheimer’s, there are a number of lifestyle and general health factors that could increase or decrease a person’s chances of developing the disease.
“However, we still do not fully understand the mechanisms behind how these factors are related to the onset of Alzheimer’s.”
Dr Ridley said there were more than 820,000 people in the UK living with dementia, and an ageing population would lead to spiralling numbers being affected.
“As there is still no certain way to prevent Alzheimer’s, research must continue to build the strongest evidence around health and environmental factors to help individuals reduce their risk.”
He added: “This new study also highlights that many cases are not due to modifiable risk factors which underlines the need to drive investment into new treatment research.”
Of the seven risk factors, the largest proportion of cases of Alzheimer’s in the US, UK and the rest of Europe can be attributed to physical inactivity.
The study says about a third of the adult population in these countries are physically inactive.
Physical inactivity is also linked to increased risks of other health problems, such as cancers and cardiovascular diseases.
A UK medical charity has called for more work into diet and dementia risk.
The best current advice is to eat a balanced diet with plenty of fruit and vegetables, not smoke, take regular exercise and keep blood pressure and cholesterol in check, said Alzheimer’s Research UK.
There is a clear need for conclusive evidence about the effect of diet on our risk of Alzheimer’s, which can only come from large-scale, long-term studies”
Dr Simon RidleyAlzheimer’s Research UK
The research looked at nutrients in blood, rather than relying on questionnaires to assess a person’s diet.
US experts analysed blood samples from 104 healthy people with an average age of 87 who had few known risk factors for Alzheimer’s.
They found those who had more vitamin B, C, D and E in their blood performed better in tests of memory and thinking skills. People with high levels of omega 3 fatty acids – found mainly in fish – also had high scores. The poorest scores were found in people who had more trans fats in their blood.
Trans fats are common in processed foods, including cakes, biscuits and fried foods.
The researchers, from Oregon Health and Science University, Portland; Portland VA Medical Center; and Oregon State University, Corvallis, then carried out brain scans on 42 of the participants.
They found individuals with high levels of vitamins and omega 3 in their blood were more likely to have a large brain volume; while those with high levels of trans fat had a smaller total brain volume.
Study author Gene Bowman of Oregon Health and Science University said: “These results need to be confirmed, but obviously it is very exciting to think that people could potentially stop their brains from shrinking and keep them sharp by adjusting their diet.”
Co-author Maret Traber of the Linus Pauling Institute at Oregon State University said: “The vitamins and nutrients you get from eating a wide range of fruits, vegetables and fish can be measured in blood biomarkers.