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

Various factors influence urinary hippuric acid concentrations; however, the role of climatic factors on such concentrations has not been thoroughly investigated.

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.

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).

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.