Body weight may play a larger role in brain aging than previously understood.
A number on the scale may say more about future brain health than previously recognized.
New research from the University of Georgia suggests that higher body mass index, or BMI, may be linked to faster cognitive decline in older adults. The finding adds to growing evidence that metabolic health, blood flow, and inflammation may all shape how the brain ages.
Some changes in memory and thinking are normal with age. People may need more time to recall names, process information, or concentrate. In healthy adults, these shifts usually happen slowly.
In this study, however, higher BMI over time was associated with sharper declines in memory, overall cognitive ability, and executive functioning. These skills help people plan, stay organized, manage emotions, focus attention, and complete everyday tasks.
A Long-Term Look at Brain Health
The researchers analyzed data from a nationally representative study that tracked more than 8,200 adults over age 50 for 24 years.
They found that each one-unit increase in BMI was linked to a faster decline in brain health.
Still, the results also offered a hopeful message.
“We found that if people managed their weight, they could significantly lower their rate of cognitive decline in just two years,” said Suhang Song, lead author of the study and an assistant professor in UGA’s College of Public Health. “That makes BMI one of the most easily modifiable risk factors when it comes to aging well.”
The link between BMI and cognitive decline was strongest in the eighth year of the study. The association was especially clear among adults older than 65.
High BMI negatively impacts brain health
Obesity, defined as a BMI of 30 or higher, has been linked to poorer brain health. According to the researchers, the exact reasons are still not fully understood.
Excess weight may contribute to inflammation, reduced blood flow, and insulin resistance. These changes could raise the risk of cognitive impairment, Alzheimer’s disease, and related dementias.
Based on BMI alone, two in five Americans are classified as obese, according to the Centers for Disease Control and Prevention.
Some researchers argue that obesity should be defined more broadly, using factors such as waist size and weight-related health conditions. Under that broader definition, 75% of Americans would be considered obese.
At the same time, more than 7 million people in the U.S. are living with dementia. The researchers said that number is expected to double by 2050.
“There are no cures for dementia,” Song said, “which is why it is critical to identify and address any modifiable risk factors we can find to prevent it.”
Reference: “Association between cumulative average BMI and cognitive decline: a 24-year cohort study” by Qianhui Xu, Meng Hsuan Sung, Zhuo Chen, Janani Rajbhandari-Thapa, Grace Bagwell Adams, M. Mahmud Khan, Ye Shen, Xiao Song, Xia Song and Suhang Song, 27 February 2026, Journal of Neurology.
DOI: 10.1007/s00415-026-13696-2
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