People who are obese in middle age are at almost four times greater risk of developing dementias such as Alzheimer's disease in later life than people of normal weight, according to a study released today.
The study, published in the journal Neurology, examined data on more than 8,500 people over the age of 65. Of the sample, 350 had been diagnosed with Alzheimer's disease or vascular dementia and a further 114 had possible dementia.
Scientists used records of the participants' height and weight in the decades before and found that those who had been overweight in middle age had a 1.8 times (80%) higher risk of being diagnosed with dementia in later life. But for obese people, classified as those having a body mass index (BMI) of 30 or above, the risk soared. People with midlife obesity had an almost four times (300%) higher risk of dementia.
"Currently, 1.6 billion adults are overweight or obese worldwide and over 50% of adults in the US and Europe fit into this category," said Weili Xu of the Karolinska Institutet in Stockholm, who led the research. "Our results contribute to the growing evidence that controlling body weight or losing weight in middle age could reduce your risk of dementia."
According to the Alzheimer's Society, around 750,000 people in the UK suffer from dementia, more than half of those with Alzheimer's. By 2021, a million people will be living with dementia.
Obese people are classified as those with BMI greater than 30, overweight people are those with a BMI between 25 and 30. Between 20 and 25 is classified as normal. Almost 30% of those in the study, 2,541 in total, had been either overweight or obese between 40 and 60 years of age.
"Although the effect of midlife overweight on dementia is not as substantial as that of obesity, its impact on public health and clinical practice is significant due to the high prevalence of overweight adults worldwide," said Xu.
Susanne Sorensen, head of research at the Alzheimer's Society, said: "This robust study adds to the large body of evidence suggesting that if you pile on the pounds in middle age, your chances of developing dementia are also increased.By eating healthily and exercising regularly, you can lessen your risk of developing dementia. Not smoking and getting your cholesterol and blood pressure checked regularly is also very important."
Xu agreed that healthy living in middle age can help to reduce a person's risk of developing dementia in later life and added that a person's experience of education also played a role in the rate of decline of the brain. "Based on this data, every one year in higher education is associated with about 10% reduced risk of overweight and obesity, and 8% decreased risk of dementia."
Exactly how excess weight can influence the degradation of the brain is not certain, but Xu said there could many possible mechanisms. "Higher body fat is associated with diabetes and vascular diseases, which are related to dementia risk," she said.
In addition, fatty tissue is the largest hormone-producing organ in the body and it can produce inflammatory molecules which may affect cognitive functioning or the process of neurodegeneration.
Sorensen said that further research was needed to find the links between being overweight and dementia. "One in three people over 65 will die with dementia, yet research into the condition is desperately underfunded."
The Alzheimer's Society has launched the Drug Discovery programme, which it says could lead to new treatments for dementia within a decade. Scientists will screen compounds that have already been licensed for other conditions, to see if they have any effect on the causes of Alzheimer's disease.
Jeremy Hughes, chief executive of Alzheimer's Society, said not enough clinical trials for dementia were taking place in the UK. "We need £4,000 every day for the next 10 years for the first phase of this groundbreaking initiative, and we are asking all those concerned with dementia to help us raise this. Together, we can transform hundreds of thousands of lives."
