People who are obese could be putting themselves at risk of dementia in later life, new research suggests.
Patients under the age of 70 who are admitted to hospital for obesity carry a higher risk of developing the condition than those who were not recorded to be obese, experts found.
They found the risk was highest among those with a record of obesity when they are in their 30s.
Estimates suggest there are currently 800,000 people with dementia in the UK, a figure which is expected to soar to over one million by 2021.
Meanwhile, data from Britain's Health and Social Care Information Centre show that in England during 2012 almost one in five people aged 25 to 34 and around a quarter of those aged 25 to 44 were obese.
About 30 per cent of the those aged 45 to 74 are obese.
The new study concluded that age could be a key factor after finding that the level of risk reduced with increasing age at the first record of obesity.
The researchers, from the University of Oxford, examined data from hospital records for the whole of England between 1999 and 2011.
When a case of obesity had been recorded the researchers then did searches for care for or death from dementia.
Their study, published in the Postgraduate Medical Journal, examined the anonymised data from 451,232 people with obesity and a control group.
They found that for those aged 30 to 39, the relative risk of developing dementia was 3.5 times higher than in those of the same age who were not obese.
They found a 70 per cent heightened risk for people in their 40s, which fell to a 50 per cent increased risk for those in their 50s. And for those aged 60 to 69 there was a 40 per cent increased risk.
The researchers observed no additional risk of dementia in people admitted to hospital for obesity in their 70s and those in their 80s were 22 per cent less likely to develop the disease.
"The risk of dementia in people who are obese in early to mid-adult life seems to be increased," the authors wrote.
"The level of risk depends on the age at which they are recorded as being obese (which may be an age or a birth cohort effect) and, while obesity at a younger age is associated with an increased risk of future dementia, obesity in people who have lived to about 60 to 80 years of age seems to be associated with a reduced risk."
Commenting on the study, Dr Clare Walton, research communications manager at the Alzheimer's Society charity, said: "These results support existing evidence that obesity in mid-life increases the risk of developing dementia."