# Environmental determinants of cardiovascular-kidney-metabolic health: interactive roles of air pollution, heat waves, and green spaces

## TL;DR

This study shows that air pollution and heat waves increase heart disease risk in people with CKM syndrome, but green spaces can help reduce this risk.

## Contribution

The study reveals novel interactive effects of air pollution, heat waves, and green spaces on cardiovascular risk in CKM syndrome.

## Key findings

- Air pollution and heat waves are linked to higher cardiovascular disease risk in CKM syndrome.
- Green spaces (NDVI) offer protection against cardiovascular disease risk.
- Interactions between PM and heat waves show greater combined risk than individual effects.

## Abstract

Cardiovascular-kidney-metabolic (CKM) syndrome, characterised by linked metabolic, renal, and cardiovascular dysfunctions, confers high cardiovascular risk and represents a major public health concern in China. Environmental exposures such as air pollution, heat waves, and limited greenness may exacerbate cardiometabolic burden. Limited studies evaluated their independent and interactive effects on CVD risk among individuals with CKM syndrome.

We assessed city-level annual environmental exposures using data from the China Health and Retirement Longitudinal Study 2011–2018. Specifically, we evaluated the effects of PM1, PM2.5, PM10, nitrogen dioxide (NO2), and heat waves on CVD incidence using Cox proportional hazards models, and examined multiplicative interactions via product terms. We quantified additive interactions using the relative excess risk due to interaction.

Exposure to air pollution (PM and NO2) and heat waves was associated with higher CVD risk, whereas a higher normalised difference vegetation index (NDVI) was protective from CVD. We observed significant interactions on both multiplicative and additive scales. Specifically, the joint association between PM and heat waves was greater than the sum of their individual risks (a positive additive interaction), suggesting that heat waves may exacerbate the risk associated with air pollution. Conversely, negative interaction terms involving NDVI suggested that higher greenness might modify the association between PM and CVD risk. These patterns were more pronounced in participants with advanced CKM stages.

Our findings provide novel evidence that multiple environmental stressors interact to influence CVD risk in the CKM population, highlighting the importance of integrated environmental and public health strategies.