# Independent and Combined Effects of Obesity and Cardiovascular Diseases on the Risk of Cognitive Impairment and Dementia: A Systematic Review and Meta-Analysis of Prospective Cohort Studies Involving 8,276,914 Participants

## TL;DR

This study finds that obesity and cardiovascular diseases are linked to dementia risk, with central obesity and stroke showing the strongest associations.

## Contribution

The study provides a comprehensive meta-analysis of the independent and combined effects of obesity and CVDs on cognitive impairment and dementia.

## Key findings

- BMI-defined obesity was associated with a lower risk of cognitive impairment.
- Central obesity increased dementia risk by 14%.
- Stroke showed the strongest association with incident dementia among CVDs.

## Abstract

Background: Dementia and cognitive impairment are increasing worldwide, particularly in older adults, imposing substantial health and societal burdens. Obesity and cardiovascular diseases (CVDs) are recognized risk factors; however, existing evidence is inconsistent, and their combined effects remain poorly understood. This study aimed to assess the independent and joint associations of obesity and CVDs with the risk of cognitive impairment and dementia through a systematic review and meta-analysis. Methods: A comprehensive literature search was conducted across three major electronic databases (PubMed, Web of Science, and Scopus) to identify relevant studies published from January 2015 through 30 June, 2025. A random-effects meta-analysis was performed to estimate the independent effects of obesity and CVDs on the outcome of interest, reporting the pooled hazard ratios (HRs) and 95% confidence intervals (CIs). The risk of bias was assessed using the Newcastle–Ottawa Scale (NOS), and the certainty of the evidence was evaluated using the GRADE approach. Results: A total of 25 studies comprising 8,276,914 participants were included. Body mass index (BMI)-defined obesity was associated with a lower risk of cognitive impairment (pooled HR = 0.85; 95% CI: 0.74–0.98; I2 = 40.5%) but showed no association with incident dementia (pooled HR = 1.00; 95% CI: 0.86–1.15; I2 = 96%). In contrast, central obesity, assessed by waist circumference (WC), was associated with a 14% increased risk of dementia (pooled HR = 1.14; 95% CI: 1.03–1.27; I2 = 96%). Coronary heart disease, stroke, and atrial fibrillation were each significantly associated with dementia risk, with pooled HRs of 1.41 (95% CI: 1.29 –1.54; I2 = 0%), 1.53 (95% CI: 1.35–1.74; I2 = 37%), and 1.30 (95% CI: 1.12–1.50; I2 = 68.8%), respectively. Evidence on the joint effects of obesity and CVD was limited to a single study, which reported that men with both conditions had a 58% higher risk of all-cause dementia compared with those of normal weight without CVD (HR = 1.58; 95% CI: 1.37–1.81). Conclusion: BMI-defined obesity was inversely associated with cognitive impairment, whereas central obesity was associated with an increased risk of dementia. Among CVDs, stroke showed the strongest association with incident dementia. However, the overall certainty of evidence across these findings was low, and these findings should be interpreted with caution.