Midlife belly fat is linked to elevated Alzheimer’s biomarkers decades later

Carrying excess belly fat during midlife is associated with elevated blood markers for Alzheimer’s disease and a higher risk of dementia decades later. The large study, published in Neurology, also indicates that this pattern reverses in old age, where weight loss often precedes cognitive decline. Identifying how body composition changes over a person’s lifespan could help medical professionals flag patients who might benefit from early interventions.

Lead author Ekaterina Zotcheva, a researcher at the Norwegian National Centre for Ageing and Health, and her colleagues sought to understand how weight changes throughout adulthood relate to the physical hallmarks of Alzheimer’s disease. Previous research investigating body fat and dementia risk has primarily relied on clinical diagnoses based on memory tests and behavioral observations. To measure brain pathology more directly, the research team looked at a blood biomarker called p-tau217.

This specific protein fragment breaks off when tau proteins in the brain become abnormally phosphorylated. These abnormal proteins then tangle together and disrupt healthy nerve cell function. High levels of p-tau217 in the blood are closely correlated with the buildup of these tangles, as well as the accumulation of amyloid plaques. Together, these plaques and tangles form the two main biological signatures of Alzheimer’s disease.

Historically, medical professionals had to rely on expensive brain imaging scans or invasive spinal taps to detect amyloid and tau accumulations in living patients. The recent development of sensitive blood tests offers a highly accessible way to track these preclinical biological processes. Because Alzheimer’s pathology can begin developing in the brain decades before memory problems surface, blood biomarkers provide a window into the earliest stages of the disease.

To assess body composition, the researchers tracked both body mass index and waist-to-height ratio. Body mass index calculates overall body size based on a person’s height and weight, but it does not account for how fat is distributed across the body. Waist-to-height ratio specifically gauges central adiposity, which is commonly referred to as belly fat. As people age, they typically lose muscle mass and gain fat around their midsection, making waist measurements a helpful indicator of changing metabolic health.

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The team analyzed data from a large population-based research project called the Trøndelag Health Study, based in Norway. The final analysis included 8,797 participants with an average age of nearly 78 years old. Researchers tracked the participants’ body mass index four times between 1984 and 2019. They also measured the participants’ waist-to-height ratio three times starting in 1995.

During the final data collection wave between 2017 and 2019, health professionals drew blood from the participants to measure p-tau217 levels. They also conducted standardized clinical assessments to diagnose any cognitive impairment. By combining the blood test results with the clinical evaluations, the team identified individuals who had biomarker-verified Alzheimer’s dementia. To isolate the effect of body weight, the researchers adjusted their models to account for education, physical activity, smoking, mental health symptoms, and the APOE e4 genetic risk factor.

The analysis revealed a distinct pattern depending on the participants’ age when their body fat was measured. Participants who had a high waist-to-height ratio in midlife had a nearly 13 percent higher concentration of p-tau217 in their blood decades later. These individuals also faced an 84 percent higher risk of developing biomarker-verified Alzheimer’s dementia compared to those with a lower midlife waist-to-height ratio. Body mass index followed a similar trajectory, with midlife obesity corresponding to higher p-tau217 levels and elevated dementia risk.

The researchers noticed modest differences between men and women when analyzing the body mass index data. For women, midlife obesity was strongly linked to an early, prodromal stage of Alzheimer’s disease. For men, midlife obesity was most closely associated with fully developed, biomarker-verified Alzheimer’s dementia. However, the overall pattern of midlife risk and late-life reversal remained consistent across both sexes.

The relationship between body fat and disease completely reversed in late life. Participants who carried excess weight or had high waist-to-height ratios at age 70 and beyond exhibited markedly lower levels of the p-tau217 biomarker. They also had a reduced risk of biomarker-verified Alzheimer’s dementia compared to their peers of the same age with lower body weight.

By tracking individuals backward from their cognitive status in old age, the researchers confirmed this shifting timeline. Participants who eventually developed Alzheimer’s disease tended to have higher body fat in midlife than those who remained cognitively healthy. As these individuals progressed toward late life and began experiencing the earliest stages of the disease, their body fat levels dropped below those of their healthy peers.

This late-life weight loss is a known phenomenon in neurodegenerative conditions. Early changes in brain regions that regulate appetite and metabolism can lead to unintentional weight loss long before severe memory problems appear. Individuals experiencing cognitive decline may also face new difficulties with shopping or preparing meals, leading to a drop in overall body weight.

The study relies on a relatively homogeneous Norwegian population, which limits how broadly the results can be applied to other demographic groups. The design also introduces a potential survival bias, as individuals had to live past age 70 to be included in the analysis. Because obesity is linked to higher mortality rates at younger ages, the participants who survived into late life may possess unmeasured health advantages.

Another limitation involves the single measurement of the p-tau217 biomarker at the very end of the study. Without repeated blood tests over the 35-year period, the researchers could not track exactly when the biomarker levels began to rise. The lower concentrations of p-tau217 observed in older adults with higher body weight might artificially underestimate the true extent of their brain pathology.

Future research could incorporate regular blood tests over a span of several decades to monitor how shifts in body fat directly coincide with changing biomarker levels. Scientists also need to investigate the biological mechanisms connecting belly fat to brain health, such as systemic inflammation or insulin resistance. Integrating genetic profiles and brain imaging could help explain why some individuals are more susceptible to weight-related cognitive decline than others.

The study, “Associations of Anthropometry Measures Across 35 Years With Late-Life Plasma P-tau217 and Dementia,” was authored by Ekaterina Zotcheva, Bjørn Heine Strand, Anita Sunde, Kay Deckers, Dag Aarsland, Nicholas J. Ashton, Henrik Zetterberg, Vegard Fykse Skirbekk, Miguel G. Borda, Gill Livingston, Archana Singh-Manoux, and Geir Selbaek. The findings provide new perspectives on how bodily changes interact with neurodegenerative decline over a human lifespan.