Both gaining and losing weight in old age raises the risk of dementia, research suggests.
A study found people over 60 who put on or shed more than 10 per cent of their BMI over two years are 20 per cent more likely to develop the memory-robbing disorder.
Obesity has been linked to inflammation, which may trigger cognitive decline, the researchers claim.
And weight loss may be a sign of another underlying condition which has its own link to dementia, such as heart disease or cancer, they add.
Both gaining and losing weight in old age raises the risk of dementia (stock)
The research was carried out by Kyungpook National University in South Korea and led by Professor Jin-Won Kwon, of the college of pharmacy.
'Both weight gain and weight loss may be significant risk factors associated with dementia,' the researchers wrote in the journal BMJ Open.
'Our results suggest that continuous weight control, disease management and the maintenance of a healthy lifestyle are beneficial in the prevention of dementia, even in later life.'
Dementia is a global health concern that is set to get worse as we continue to live for longer.
Some 46.8million people worldwide had been diagnosed with the condition in 2015, which cost around £642billion ($818billion) that year alone.
Meanwhile, the global prevalence of obesity has increased by more than 100 per cent over the past four decades.
Because dementia is an irreversible, progressive condition, studies have focused on how to prevent it, with many pointing to BMI.
Obesity in middle age has been linked to cognitive decline, however, studies that show how excess weight may cause dementia have been inconsistent.
A GLOBAL CONCERN
Dementia is an umbrella term used to describe a range of progressive neurological disorders, that is, conditions affecting the brain.
There are many different types of dementia, of which Alzheimer's disease is the most common.
Some people may have a combination of types of dementia.
Regardless of which type is diagnosed, each person will experience their dementia in their own unique way.
Dementia is a global concern but it is most often seen in wealthier countries, where people are likely to live into very old age.
HOW MANY PEOPLE ARE AFFECTED?
The Alzheimer's Society reports there are more than 850,000 people living with dementia in the UK today, of which more than 500,000 have Alzheimer's.
It is estimated that the number of people living with dementia in the UK by 2025 will rise to over 1 million.
In the US, it's estimated there are 5.5 million Alzheimer's sufferers. A similar percentage rise is expected in the coming years.
As a person's
