# Serum trihalomethanes and cognitive decline: investigating environmental risk factors for neurodegenerative diseases

## TL;DR

This study finds that higher levels of trihalomethanes in the blood are linked to increased cognitive decline, especially in older adults and those with health conditions.

## Contribution

The study identifies trihalomethanes as potential environmental neurotoxicants linked to cognitive impairment.

## Key findings

- Higher serum THM concentrations were associated with a 2.50-fold increased risk of cognitive impairment.
- BDCM showed a non-linear association with cognitive decline, particularly in the animal fluency test.
- Older adults, females, and those with hypertension or diabetes were more susceptible to THM-related cognitive impairment.

## Abstract

Trihalomethanes (THMs), byproducts of water chlorination, are pervasive in drinking water supplies and have known systemic toxicity. However, their potential neurotoxic effects, particularly on cognitive function, remain poorly understood. This study investigates the association between serum THM concentrations and cognitive decline, aiming to identify environmental risk factors for neurodegenerative diseases.

Data were drawn from the National Health and Nutrition Examination Survey (NHANES) 2011–2014 cohort. A final analytic sample of 743 participants aged 60 years or older was analyzed. Serum concentrations of four THM species—chloroform, bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM)—were measured. Cognitive performance was assessed using CERAD Word Learning and Delayed Recall, animal fluency test (AFT), and digit symbol substitution test (DSST). Cognitive impairment was defined as scores below the 25th percentile. Multivariate logistic regression, restricted cubic splines (RCS), and subgroup interaction analyses were used to explore associations.

Higher serum THM concentrations were significantly associated with increased odds of cognitive impairment. In the fully adjusted model, individuals in the highest quartile of total THMs (TTHMs) had a 2.50-fold higher risk (95% CI: 1.68–3.71) compared to the lowest quartile. RCS analysis revealed a non-linear association between BDCM and cognitive decline, particularly in the AFT. Subgroup analysis indicated that older adults (≥70 years), females, and individuals with hypertension or diabetes were more susceptible to THM-related cognitive impairment.

Elevated serum THM levels are independently associated with cognitive impairment, particularly in vulnerable populations. These findings suggest that THMs may act as environmental neurotoxicants contributing to cognitive decline. Public health efforts to reduce THM exposure could play a role in mitigating the risk of neurodegenerative diseases.