In a study of 1.3 million people in the U.S. and Europe, scientists have found that having a higher BMI (body mass index) is associated with a higher risk of dementia.
The good news: The longer we study dementia, the more controllable risk factors we find.
The bad news: Obesity plagues many Western countries, particularly as a population ages. In the U.S., 36.5 percent of adults are obese. In the U.K. that figure hovers around 27 percent. Both are expected to rise to 41 percent and 34 percent, respectively, by 2025.
The study discovered two key findings: one, higher levels of body fat, which blocks blood flow to the brain and increases risk of diabetes and cardiovascular disease, were associated with an increased risk of dementia in later life; and two, being underweight later in life was associated with the impending onset of dementia.
“…People who develop dementia may have a higher-than-average body mass index some 20 years before dementia onset, but [those] close to [developing] overt dementia have a lower BMI than those who remain healthy,” said lead author Mika Kivimäki, a professor at University College London’s Institute of Epidemiology & Health.
With each five-unit increase in BMI, researchers saw dementia risk go up 16 to 33 percent. To put that into perspective, five units of BMI translates to 32 pounds in a person who is five feet seven inches tall.
The findings contradict an earlier study from 2015, which actually found being overweight in middle age to be protective. But this study followed participants for a longer period of time—38 years—and also found that weight loss in pre-clinical dementia can start up to ten years before a diagnosis, which may have skewed the previous study.
The new study supports another finding that going to the gym lowers dementia risk amongst people in their 60s and 70s. That study, conducted in Australia on 400 people, found that being active lowered the rate of brain shrinkage.
Doctors who study dementia, like Dr. Miia Kivipelto, M.D., have recommended diets with lots of fruits and vegetables and healthy fats like fish and olive oil. You can read more about the diet doctors recommend for staving off dementia here.