Supporting earlier research, a study involving 8,534 older adults (65+; mean age 74.4) has found those who were obese in middle age had almost four times (300%) more risk of developing dementia. Those who were overweight in middle age had a 1.8 times (80%) higher risk of developing dementia.
Participants were drawn from the Swedish Twin Registry. Height and weight had been measured at a mean age of 43.3, and 29.8% were defined as overweight or obese. Dementia was diagnosed in 350 participants (4.1%), with a further 114 (1.33%) diagnosed as questionable.
Apart from the clear links between excess weight and risk factors such as cholesterol, diabetes, hypertension, inflammation, there are also correlational factors. Higher education (which helps protect against brain damage) was also associated with about 10% reduced risk of overweight and obesity.
 . Midlife overweight and obesity increase late-life dementia risk. Neurology [Internet]. 2011 ;76(18):1568 - 1574. Available from: http://www.neurology.org/content/76/18/1568.abstract