Even a few extra pounds in midlife can increase the risk of dementia, study finds

Packing on even a few extra pounds in midlife can increase the risk of developing dementia, such as Alzheimer’s disease, by 70% or more, Swedish researchers reported Monday.

Earlier studies had shown an increased risk from being obese, but the new research reported in the journal Neurology is the first to show that simply being overweight is enough to increase the risk. “Our results contribute to the growing evidence that controlling body weight or losing weight in middle age could reduce your risk of dementia,” co-author Dr. Weili Xu of the Karolinska Institutet in Stockholm said in a statement.

Xu and her colleagues studied 8,534 twins over the age of 65 in the Swedish Twin Registry. The participants’ heights and weights had all been measured 30 years earlier. Among the elderly twins, 350 had been diagnosed with dementia and 114 with possible dementia.

The researchers stratified the subjects according to their body mass index 30 years earlier. Body mass index or BMI is a commonly used, albeit crude, measure of obesity. The researchers defined overweight as having a BMI between 25 and 30 and obesity as having a BMI over 30. Nearly 30% of the twins, 2,541, were either overweight or obese during middle age.

The researchers found that 26% of those without dementia had been overweight in midlife, compared with 36% of those with questionable dementia and 39% of those with diagnosed dementia. Three percent of those with no dementia had been obese in midlife, compared with 5% of those with questionable dementia and 7% of those with diagnosed dementia.

Surprisingly, however, when the team looked at twin pairs in which only one had dementia, they found no relationship between being overweight or obese and dementia. That suggests, Xu said, that genetics and environmental factors in early life may play a significant role in the relationship. Also, she added, the number of such twin pairs might not have been large enough to show the link.

The causes of the relationship are not clear. One possibility is that the inflammation associated with being overweight may damage brain cells, producing the dementia. A higher BMI is also associated with diabetes and vascular disease, either or both of which could contribute to dementia.