Large swings in body weight linked to higher dementia risk, major analysis suggests

What is dementia?

Dementia refers to a group of conditions marked by progressive decline in memory, thinking, and daily functioning. The most common types are Alzheimer's disease and vascular dementia, and as populations age globally, dementia represents an increasing burden on individuals, families, and health systems.

Which study found this link?

The findings come from a 2025 meta-analysis titled "Body weight and BMI variability linked to dementia risk: A meta-analysis," conducted by Sitian Fang and colleagues. The study examined long-term patterns of body weight and BMI and their relationship to later dementia diagnosis.

Why look at weight fluctuations?

Most previous research has focused on static weight or BMI, but many people experience weight swings due to lifestyle changes, illness, or aging. These fluctuations—known as body weight variability—can reflect underlying metabolic instability. The authors aimed to determine whether such instability is also related to dementia risk.

About the study

The meta-analysis combined data from 10 datasets across 9 cohort studies, including nearly 4.23 million participants from several countries. Studies followed adults for up to 36 years, measuring weight or BMI at multiple time points and later recording dementia diagnoses. Participants were grouped by how much their weight changed over time.

Key findings

Individuals with the highest levels of weight variability had a 36% higher risk of developing dementia compared with those whose weight remained more stable. This association was consistent across both body-weight-based and BMI-based measures.

The pattern held for major dementia subtypes, including Alzheimer's disease and vascular dementia, and appeared across men and women, various study designs, and different follow-up durations.

Why weight fluctuations may matter

Large swings in weight may reflect metabolic or inflammatory processes that also influence long-term brain health. The authors note that subtle early cognitive changes could also cause weight instability years before a formal diagnosis, meaning both directions of influence are possible.

Limitations and challenges

Because all included studies were observational, the findings cannot prove causation. Reverse causation remains a possibility, and the substantial variability between studies—including differences in how weight fluctuations were measured—adds uncertainty.

Why this study is important

This is the first large systematic analysis to specifically evaluate weight variability as a dementia risk factor. By synthesizing data from more than four million adults, the study provides strong evidence that long-term weight stability may be an important indicator of healthy aging and brain health.

Looking ahead

Further research using standardized weight-tracking methods and long-term follow-up is needed to clarify mechanisms and determine whether maintaining stable weight can help lower dementia risk. Still, tracking weight patterns over time, rather than relying on a single measurement, may offer clinicians a valuable tool for identifying individuals at elevated risk.

More information:

Sitian Fang et al, Body weight and BMI variability linked to dementia risk: A meta-analysis. Biomol Biomed [Internet]. 2025 Jul. 7 [cited 2025 Dec. 8];25(12):2632–2646.

Available from: https://doi.org/10.17305/bb.2025.12626

Journal information: Biomolecules and Biomedicine

Provided by: Association of Basic Medical Sciences of FBIH

Provided by Association of Basic Medical Sciences of FBIH