People who are overweight or obese when they are diagnosed with dementia tend to live longer than those in a normal weight range, according to a new study. The findings underscore the need for greater attention to nutrition among those with dementia and suggest that one’s weight at the time of diagnosis may provide meaningful prognostic information about survival.
However, previous research has shown that people who are overweight or obese at midlife are more likely to develop dementia later in life. So researchers wondered if these counterintuitive findings point to an underlying reason why excess weight may help people with dementia live longer—for instance, having greater energy reserves—or if they are the result of biases.
The study, published in the Journal of Alzheimer's Disease, used data from the Health and Retirement Study, an ongoing, nationally representative study of U.S. adults 51 and older conducted by the University of Michigan. Using data collected from 1998 through 2022, the study included 4,523 individuals who were dementia-free at first but later developed the disease. Given the long timespan of the study, the researchers could track individuals’ weight before and at their dementia diagnosis, as well as how long they lived after being diagnosed.
The researchers found that people with dementia who were overweight or obese at the time of diagnosis had a significantly lower mortality risk than those of normal weight, even after adjusting for factors such as chronic conditions, smoking and demographics. Individuals who were overweight (body mass index of 25 to 29.9) had a 16 percent lower risk of death, while those with class 1 obesity (BMI of 30 to 34.9) had a 27 percent lower risk, and those with class 2 and 3 obesity (BMI equal to or greater than 35) had a 22 percent lower risk.
Importantly, additional analyses evaluating several forms of potential bias did not suggest that they were significant contributors to the observed associations between weight status and mortality. From a physiological standpoint, the researchers describe why excess weight could benefit people with dementia, including having greater catabolic reserves in the form of energy stores or more muscle mass.
Data from NYU