Obesity linked to up to 27% lower risk of death in dementia

Researchers from Columbia University Mailman School of Public Health and NYU School of Global Public Health found that body weight at the time of diagnosis may provide important clues about how long someone with dementia is likely to live. Their findings, published in the Journal of Alzheimer's Disease, also highlight the importance of proper nutrition for people living with the condition.

The results are particularly intriguing because obesity is well established as a risk factor for several serious health problems, including heart disease and diabetes. Being overweight or obese during middle age is also associated with a greater likelihood of developing dementia later in life. However, previous research has suggested that the relationship may reverse once dementia has developed, with higher body weight linked to better survival.

"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," said corresponding author Yuan Zhang, PhD, assistant professor of Sociomedical Sciences at Columbia Mailman and in the Butler Columbia Aging Center.

Obesity Linked to Up to 27% Lower Risk of Death

The researchers found substantial differences in survival based on body weight at the time of dementia diagnosis. Compared with individuals in the normal weight range, those who were overweight or obese had a significantly lower risk of death, even after the researchers accounted for smoking, existing medical conditions, and demographic characteristics.

People classified as overweight (body mass index of 25 to 29.9) had a 16 percent lower risk of death. Those with class 1 obesity (BMI of 30 to 34.9) had an even larger reduction of 27 percent, while individuals with class 2 and 3 obesity (BMI equal to or greater than 35) had a 22 percent lower risk.

Despite these striking differences, the researchers caution that the findings should not be interpreted as a recommendation for people with dementia 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. 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," said Virginia Chang, associate professor of Social and Behavioral Sciences at NYU School of Global Public Health and the study's first author.

Tracking Weight and Dementia Over 24 Years

To investigate the connection, Zhang, Chang, and their colleagues examined information from the Health and Retirement Study, a nationally representative research project that follows Americans ages 51 and older.

The team analyzed records collected between 1998 and 2022, focusing on 4,523 participants who did not have dementia when they entered the study but subsequently developed the condition.

Because the data covered such a long period, the researchers could examine how participants' weight changed in the years leading up to their diagnosis. They could also determine their weight when dementia was identified and track their survival afterward.

This extended timeline was especially important because scientists have questioned whether the apparent benefit of higher body weight is genuine or simply reflects misleading patterns in the data. One possibility is that having additional fat or muscle gives patients resources that help them withstand the physical effects of dementia. Another is that the association arises from factors that earlier studies did not adequately consider.

Could Weight Loss Explain the Dementia Paradox?

One major concern involves weight loss that occurs before dementia becomes clinically apparent.

Earlier research by Zhang and Chang found that people can begin losing weight as much as 10 years before a dementia diagnosis, with the decline becoming more pronounced as the disease approaches.

This creates a potential problem for studies that measure weight only at the time dementia is diagnosed. Some individuals classified as having a normal weight may previously have been heavier and lost weight because of 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 other possible distortions. Restricting an analysis to people who develop dementia can create misleading relationships between obesity and mortality, even when the underlying connection is more complicated.

Another concern is known as "survivor" bias. Since people with obesity face an increased risk of dying from certain illnesses before reaching the age when dementia typically develops, those 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 they examined were unlikely to be major drivers of the observed connection between higher weight and lower mortality.

Why Extra Weight Might Help People With Dementia

Although the precise explanation remains unknown, the researchers identified several biological reasons why additional body weight could be advantageous for someone already living with dementia.

One possibility involves the body's energy reserves. People with more stored fat or greater muscle mass may be better equipped to withstand periods of poor nutrition and the physical deterioration that can accompany the disease.

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.

"Nutrition can be a big problem for people with dementia," said Chang. "They may experience wasting and an inability to eat, which can be due to changes in the brain's central drive, leading to loss of appetite and initiative, increased energy expenditure, and difficulties feeding themselves."

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.

The researchers emphasize that important questions remain unanswered. Even after examining multiple potential biases and identifying plausible biological explanations, they cannot say for certain why overweight and obese participants experienced lower mortality.

Nevertheless, Zhang and Chang believe that weight at the time of a dementia diagnosis could provide valuable information about a patient's likely survival. The results also reinforce the importance of recognizing and addressing nutritional problems in people with dementia.

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 (grant numbers R00AG070274, R00AG075317).