New Delhi: Obesity is usually discussed as a ticking time bomb for health, raising the risk of diabetes, heart disease and even dementia. But once dementia sets in, the relationship between weight and health may be more complicated.
A new study has found that people who are overweight or obese when diagnosed with dementia are more likely to live longer than those whose weight fell within the normal range. However, researchers caution that the finding does not indicate that extra kilos are protective. Instead, the study raises questions about how the disease affects the body long before a diagnosis, and why nutritional reserves may matter in the years that follow.
Published in the Journal of Alzheimer’s Disease on 30 September, the study was conducted by researchers at Columbia University’s Mailman School of Public Health and New York University’s School of Global Public Health. Scientists analysed data from the Health and Retirement Study, a long-running, nationally representative survey of adults aged 51 and above in the United States, from 1998 to 2022.
Their sample included 4,523 people who were dementia-free when they entered the study but developed dementia later. Researchers tracked participants’ weight before and at dementia diagnosis, and then examined how long they survived after the neurodegenerative disease set in.
The results were striking.
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What did the study find?
People with dementia who were overweight, with a body mass index (BMI) of 25 to 29.9, had a 16 per cent lower risk of early death than those with a normal BMI. Those with class 1 obesity, a BMI of 30 to 34.9, had a 27 per cent lower risk, while people with class 2 or 3 obesity, a BMI of 35 or above, had a 22 per cent lower risk. The association persisted even after researchers accounted for other chronic illnesses, smoking and demographic differences.
The findings do not contradict evidence linking obesity in midlife to a higher risk of developing dementia. Instead, they point to a different question: what role does body weight play once the disease has developed?
One possible explanation lies in how dementia affects eating and metabolism. People with dementia may lose their appetite, struggle to feed themselves or experience changes in energy expenditure as the disease alters brain function. Weight loss can begin as many as 10 years before diagnosis and accelerate in the years immediately preceding it.
That means someone classified as having a “normal” weight at diagnosis may already have lost considerable weight because of the disease. Higher weight, meanwhile, may indicate greater energy reserves that help the body withstand illness, reduced food intake and physical decline.
Researchers also examined whether the findings could be explained by biases in how participants were classified or selected for the study. Their additional analyses did not suggest that these factors were major contributors to the observed association.
From a biological perspective, the authors point to what are known as “catabolic reserves”: energy stores and potentially greater muscle mass that may help patients endure periods of illness and declining food intake.
“Nutrition can be a big problem for people with dementia,” said Virginia Chang of NYU, the study’s first author, noting that changes in the brain can lead to appetite loss and difficulties feeding oneself.
The findings are not evidence that people with dementia should gain weight, nor do they establish that higher weight itself prolongs life. Instead, the researchers suggest that weight at diagnosis could provide useful information about a patient’s prognosis, while highlighting the importance of identifying and addressing nutritional problems.
For families and clinicians, the researchers warned, unexplained weight loss in an older person should not automatically be dismissed as a consequence of ageing. It can be an early sign of cognitive decline, and maintaining adequate nutrition may be an important part of dementia care.
(Edited by Insha Jalil Waziri)