Climatic effects on urinary hippuric acid concentrations: a three-year occupational health study in a manufacturing workforce

Objectives: Various factors influence urinary hippuric acid concentrations; however, the role of climatic factors in this process has not been thoroughly investigated. Methods: This study examined the correlation between urinary hippuric acid concentrations and climatic factors. Data were obtained from health examinations of 2,236 employees at a large manufacturing company who used organic solvents over a three-year period. Each participant underwent health examinations for organic solvent users during both the summer (June to August) and winter (December to February). Urinary hippuric acid concentrations were log-transformed, and a linear mixed-effects model was applied to assess their association with average temperature, relative humidity, and atmospheric pressure recorded in Nagoya City, Japan. Results: In a multivariate linear mixed-effects model including all meteorological variables, average temperature showed a significant positive association with log-transformed urinary hippuric acid concentrations (Estimate = 0.013, 95% CI: 0.007 to 0.020, p < 0.001). This corresponds to an estimated 1.3% increase in urinary hippuric acid concentrations per 1°C rise in temperature. In contrast, neither average atmospheric pressure nor relative humidity showed a statistically significant associations (p = 0.981 and p = 0.817, respectively). Among the confounding variables, smoking was significantly positively associated with concentration (p = 0.001), whereas alcohol consumption showed a significant negative association (p = 0.031). Conclusion: Urinary hippuric acid concentrations exhibited seasonal variation among workers at a large manufacturing company, with elevated levels observed during the summer. These findings underscore the importance of considering climatic factors when interpreting urinary metabolic biomarkers.