By 2050, there are projected to be more than 150 million instances of dementia worldwide, a sharp increase from the 50 million cases that exist today.

A global epidemic of obesity, generally measured by body mass index (BMI), persists, and past research revealed that obesity in middle age may raise the risk of dementia. The link between BMI and the risk of dementia, however, is still not obvious.

These findings appear online in Alzheimer's & Dementia: The Journal of the Alzheimer's Association. Now, researchers from Boston University Chobanian & Avedisian School of Medicine and Chinese Academy of Medical Sciences & Peking Union Medical College, have found that different patterns of BMI changes over one's life course may be an indicator of a person's risk for dementia.

"These findings are important because previous studies that looked at weight trajectories didn't consider how patterns of weight gain/stability/loss might help signal that dementia is potentially imminent," explained corresponding author Rhoda Au, PhD, professor of anatomy and neurobiology.

Through the Framingham Heart Study, a group of participants was followed for 39 years and their weight was measured approximately every 2-4 years. The researchers compared different weight patterns (stable, gain, loss) among those who did and did not become demented.

They found the overall trend of declining BMI was associated with a higher risk of developing dementia. However, after further exploration, they found a subgroup with a pattern of initial increasing BMI by declining BMI, both occurring within midlife, which appeared to be central to the declining BMI-dementia association.

Au points out that for individuals, family members, and primary care physicians, it is relatively easy to monitor weight.

"If after a steady increase in weight that is common as one gets older, there is an unexpected shift to losing weight post midlife, it might be good to consult with one's healthcare provider and pinpoint why. There are some potential treatments emerging where early detection might be critical in the effectiveness of any of these treatments as they are approved and become available," she added.

The researchers hope this study will illustrate that the seeds for dementia risk are being sowed across many years, likely even across the entire lifespan.

"Dementia is not necessarily inevitable and monitoring risk indicators such as something as easy to notice as weight patterns, might offer opportunities for early intervention that can change the trajectory of disease onset and progression."