Scientists found out when excess weight saves lives

People who are overweight or obese at the time of dementia diagnosis appear to live longer than those whose weight is within the normal range. This unexpected conclusion was reached by the authors of a new study published in the Journal of Alzheimer's Disease.

The reasons behind this phenomenon remain a mystery for now, but the findings suggest that body weight at the time of diagnosis may carry important prognostic information about survival and indicate that nutrition in dementia needs to receive far more attention.

"This does not mean that patients with dementia should try to gain weight — our study was not designed to test that question. But the results show that weight can serve as a useful prognostic signal at the time of diagnosis. They also confirm that nutrition is a key factor in health and survival in dementia," said lead author Virginia Chang from the New York University School of Global Public Health.

Obesity has long been recognized as a risk factor for numerous diseases, including heart disease and diabetes. It is also known that people who are overweight in middle age are more likely to develop dementia later in life. Nevertheless, a number of studies demonstrate a paradoxical picture: among those already diagnosed with dementia, obesity is associated with better survival.

Researchers were concerned with the question: is there a real reason behind these counterintuitive results — for example, greater energy reserves in the body — or is it all due to data errors? One possible source of distortion lies in the fact that people with dementia often begin losing weight long before diagnosis, sometimes a full decade earlier. Thus, the "normal weight" group may have included patients with a more advanced stage of the disease.

Chang, Zhang, and their colleagues turned to data from the Health and Retirement Study — a large-scale ongoing national study of American adults aged 51 and older, conducted by the University of Michigan. Having analyzed information from 1998 to 2022, they selected 4,523 individuals who initially did not have dementia but subsequently developed it. The lengthy observation period made it possible to track weight dynamics both before and at the time of diagnosis, as well as lifespan after it.

The results proved quite telling: dementia patients who were overweight or obese at the time of diagnosis demonstrated a significantly lower risk of mortality compared to those whose weight was normal — even after adjusting for chronic diseases, smoking, and demographic factors. Among overweight individuals (BMI 25–29.9), the risk of death was 16% lower; with class 1 obesity (BMI 30–34.9), it was 27% lower; and with class 2 and 3 obesity (BMI 35 and above), it was 22% lower.

Additional analyses aimed at identifying several forms of potential data distortion did not find any significant impact on the observed patterns.

From a physiological standpoint, the researchers offer an explanation for why additional weight may prove beneficial in dementia: the body has greater catabolic reserves in the form of energy stores or muscle mass. "Because this finding is somewhat counterintuitive, it is critically important to understand whether it is simply a statistical error. Our analyses show that the main sources of bias that we tested do not explain the survival advantage associated with greater weight," —