A new study has shown that, in people over 50, every unit increase in Body Mass Index (BMI) accelerates Alzheimer's onset by nearly seven months.
According to research from The National Institute Of Ageing, being obese or overweight at midlife, as measured by body mass index (BMI), could predict earlier onset of the neurodegenerative disorder.
Alzheimer's disease is the most common form of dementia, affecting almost 500,000 people in the UK, says the NHS.
The new research contradicts a study published earlier this year, that suggested obesity in middle-age could reduce the risk of dementia in later life.
Scientists looked at the relationship between weight at midlife and Alzheimer's in 1,394 cognitively healthy volunteers.
They found that after 14 years of testing, 142 participants eventually developed the disease.
In the study, which was published in the journal Molecular Psychiatry, researchers used brain imaging to analyse how healthy the volunteers' brains were. Brain imaging detects amyloid - a protein associated with Alzheimer’s development.
They found that those with higher midlife BMI had more amyloid deposits in the precuneus, a brain region that often shows the earliest signs of Alzheimer’s-related changes.
"Dementia in old age is mostly related to a decrease in blood supply to the brain as the tiny blood vessels age and block off," explains Dr Helen Webberley, dedicated GP for Oxford Online Pharmacy.
"When the tiny vessels at the very edges of the brain stop allowing enough blood through, tiny parts of the brain die.
"This causes problems with memory, speech and other bodily functions, depending on which part of the brain is affected."
She adds: "We know that this small vessel disease is affected by the usual risk factors such as diabetes, smoking and obesity so it is not surprising that there may be a correlation between BMI and the onset of dementia."
The link between BMI and Alzheimer's echoes previous research suggesting obesity could increase risk in developing the disease.
The study from earlier this year, which was published in the Journal of Neurology Neurosurgery & Psychiatry, analysed data from over 300 large studies in order to identify risk factors of the disease.
They found that the nine most common risk factors for developing Alzheimer's disease are: obesity, low education attainment, high homocysteine levels, depression, high blood pressure, carotid artery narrowing, frailty and type 2 diabetes in the Asian population.
Dr Clare Walton, research manager at Alzheimer's Society, tells HuffPost UK Lifestyle: "Evidence shows that lifestyle can have an influence on the development of dementia, although the research on obesity has so far produced inconsistent results.
"We know that dementia can begin to develop years or maybe decades before symptoms begin and so keeping healthy through midlife and into later life is important for reducing dementia risk.
"The best ways to keep healthy and reduce your risk of developing dementia include eating a balanced diet, not smoking and taking regular physical exercise."
Dr Webberley notes that "more work needs to be done in this area to prove the exact relationship between BMI and the age of onset".
"It is yet another reminder of the fact that our lifestyle in our youth directly affects us in old age," she adds.