Climatic effects on urinary hippuric acid concentrations: a 3-year occupational health study in a manufacturing workforce

Objectives: Various factors influence urinary hippuric acid concentrations; however, the role of climatic factors on such concentrations 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 2236 employees at a large manufacturing company who used organic solvents over a 3-year period. Each participant underwent a health examination for organic solvent use 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: 0.007-0.020; P<.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 association (P=.981 and P=.817, respectively). Among the confounding variables, smoking was significantly positively associated with concentration (P=.001), whereas alcohol consumption showed a significant negative association (P=.031). Conclusions: 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.