A new study published in the Journal of Alzheimer’s Disease reveals a counterintuitive link between body weight and survival in patients with dementia. Researchers from Columbia University Mailman School of Public Health and NYU School of Global Public Health found that individuals who are overweight or obese at the time of diagnosis tend to live longer than those with a normal body weight. The findings challenge long-held assumptions about the relationship between obesity and health outcomes in elderly populations.
Survival Advantage Linked to Higher Body Weight
The analysis examined data from the Health and Retirement Study, a nationally representative project tracking Americans aged 51 and older. The team focused on 4,523 participants who did not have dementia when they entered the study but developed the condition later. By tracking these individuals from 1998 to 2022, researchers could observe weight changes leading up to diagnosis and survival rates afterward.
Compared to individuals in the normal weight range, those classified as overweight had a 16 percent lower risk of death. The survival advantage was even more pronounced for those with class 1 obesity, who showed a 27 percent reduction in mortality risk. Individuals with class 2 and 3 obesity, defined by a body mass index of 35 or higher, experienced a 22 percent lower risk of death. These results held true even after accounting for smoking status, existing medical conditions, and demographic factors.
Yuan Zhang, PhD, assistant professor of Sociomedical Sciences at Columbia Mailman and in the Butler Columbia Aging Center, noted that the findings are somewhat unexpected given the known health risks associated with obesity. “Because this finding is somewhat counterintuitive, an important question is whether it could simply be an artifact of bias. Our analyses suggest that the major sources of bias we examined do not explain the survival advantage associated with higher weight,” Zhang said.
Addressing Potential Biases in Research
Previous research has suggested that the relationship between weight and dementia might reverse once the disease develops. However, scientists have long questioned whether this apparent benefit is genuine or a result of misleading data patterns. One major concern involves weight loss that occurs before dementia becomes clinically apparent. Earlier work by the same research team indicated that people can begin losing weight as much as 10 years before a diagnosis, with the decline becoming more pronounced as the disease approaches.
This creates a potential distortion in studies that measure weight only at the time of diagnosis. Some individuals classified as having a normal weight may previously have been heavier and lost weight due to the developing disease. If those individuals are already experiencing more advanced illness, they may face a greater risk of death, making higher body weight appear beneficial by comparison. The researchers also considered “survivor” bias, where people with obesity who survive long enough to receive a dementia diagnosis may represent an unusually healthy group.
To determine whether these factors explained the findings, the team performed additional analyses designed to evaluate several potential sources of bias. The results indicated that the biases examined were unlikely to be major drivers of the observed connection between higher weight and lower mortality. Despite these rigorous checks, the precise biological explanation for the survival advantage remains unknown.
Nutrition and Energy Reserves in Dementia Care
Virginia Chang, associate professor of Social and Behavioral Sciences at NYU School of Global Public Health and the study’s first author, emphasized that the findings should not be interpreted as a recommendation for patients to gain weight. “This doesn’t mean that patients with dementia should attempt to become overweight or obese, as our study was not designed to test that question,” Chang said. “But our findings do suggest that weight status may serve as a useful prognostic signal for survival at the time of dementia diagnosis. They also support the notion that nutrition is a key factor in the health and survival of people with dementia.”
Dementia can interfere with eating in several ways. Changes in brain function may reduce appetite or motivation to eat, while some patients experience increased energy needs or gradually lose the ability to feed themselves. Over time, these problems can contribute to significant weight loss, muscle wasting, and declining health. Having additional energy stores or muscle tissue could potentially help patients cope with these challenges, although the study did not establish that these factors directly explain the survival differences.
Additional study authors include Eleanor Hayes-Larson of the University of Southern California and Hui Zheng of the University of Toronto. The research received funding from the National Institutes of Health.
Source: ScienceDaily
