Women who are obese throughout life are more likely to lose brain tissue - a state linked to cognitive decline, say Swedish researchers at the Sahlgrenska University Hospital in Göteborg that carried out the study.
"An overweight or obese BMI was linked to a loss of tissue specifically in the temporal lobe. The risk of atrophy increased 13 to 16 per cent per 1.0 kg/m2 increase in BMI," report the scientists at Sahlgrenska University Hospital and the Medical College of Wisconsin in Milwaukee.
"Obesity is another factor that should be actively intervened upon to reduce diseases of advanced ageing," added Deborah Gustafson, a researcher on the study.
Almost one third of people living in the European Union are overweight and more than one in ten is now obese, according to European Association for the Study of Obesity. And the numbers of children who are overweight is set to rise from 20 per cent to 25 per cent by 2008, according to Datamonitor.
Growing evidence suggests that obesity significantly increases the risk of heart disease, diabetes and other life-threatening conditions.
The Swedish researchers studied the relationship between body mass index and brain atrophy (loss of brain tissue) in 290 women born between 1908 and 1922 that had four follow-up examinations between 1968 and 1992.
During the final exam, they had a computed tomography (CT) scan to measure for any loss of brain tissue. Body mass index (BMI) is a measure of body fat that shows weight adjusted for height. Overweight is a BMI of 25 to 30 kg/m2. Obesity is a BMI of 30 kg/m2 and above.
"This study indicates that a high BMI is a risk factor for dementia in women. Other studies have reported similar findings," said Gustafson.
"An overweight or obese BMI was linked to a loss of tissue specifically in the temporal lobe. The risk of atrophy increased 13 to 16 per cent per 1.0 kg/m2 increase in BMI," the scientists commented.
Nearly 50 per cent (144) of the women had temporal atrophy. At the time of CT scan, their body mass index was an average of 27 kg/m2, which was 1.1 to 1.5 kg/m2 higher than the women without brain atrophy. Overall the women's BMI increased over the 24-year period, but the increase was greater for those who lost tissue in the temporal lobe.
The researchers did not pinpoint a reason why obesity leads to brain atrophy but they said there are several possible mechanisms.
"Obesity is related to ischaemia, hypertension, and cerebrovascular and cardiovascular diseases. These conditions contribute to an unhealthy vascular system, and therefore, to a higher dementia risk," said Gustafson. "Obesity may also increase the secretion of cortisol, which could lead to atrophy."
Full findings are published in the November 23 issue of Neurology, the journal of the American Academy of Neurology.