Even though the biggest factor in the development of dementia is age, new research, reported on the BBC website, suggests that overweight middle-aged people are 71% more likely to develop dementia than those with a normal weight.
A study of some 8,534 Swedish twins, in the journal Neurology suggests just being overweight is also a risk factor.
With about one out of every 20 people above the age of the 65 having dementia, the Alzheimer's Society say that a healthy lifestyle could reduce this risk.
According to the study, those with a body mass index (BMI) - which measures weight relative to height that is greater than 30, who are classified as obese, were 288% more likely to develop dementia than those with a BMI between 20 and 25. The clinically overweight, who have a BMI between 25 and 30, were 71% more likely.
Dr Weili Xu, from the Karolinska Institute in Stockholm, told the BBC: "We found in this study that being overweight is also a risk for dementia later in life. The risk is not as substantial as for [the] obese, but it has public health importance because of this large number of people worldwide who are overweight." 1.6 billion adults are overweight worldwide.
Alzheimer's Research UK head of research, Dr Simon Ridley, said: "This study adds to existing evidence that excess weight in middle age could increase our risk of developing dementia.
"It's likely that dementia is caused by a complex mix of genetic, environmental and lifestyle factors. However, we still need to know much more about the causes of dementia if we are to find an effective treatment that is so desperately needed."