Original article Table 3 Comparisons of urinary malondialdehyde and 1-hydroxypyrene levels between kitchen (n = 171) and service staff (n = 117) Marker MDA 1-OHP Smoking status Smoker (n = 134) Non-smoker (n = 154) All (n = 288) Smoker (n = 134) Non-smoker (n = 154) All (n = 288) Service staff 293.3 (213.7) (n = 56) 244.2 (164.4) (n = 61) 267.2 (189.9) (n = 117) 6.9 (8.8) (n = 56) 2.4 (4.3) (n = 61)* 4.4 (7.0) (n = 117)* Kitchen staff 398.0 (380.0) (n = 78)* 344.2 (243.7) (n = 93){ 369.0 (314.0) (n = 171){ 6.5 (8.4) (n = 78) 6.0 (8.0) (n = 93){ 6.2 (8.2) (n = 171)* *Kitchen staff differ significantly from service staff at p,0.05 by Student’s t test; {kitchen staff differ significantly from service staff at p,0.01 by Student’s t test; {kitchen staff differ significantly from service staff at p,0.001 by Student’s t test. Values are mean (SD) (mmol/mol creatinine). 1-OHP, 1-hydroxypyrene; MDA, malondialdehyde. non-smoking worker urinary MDA and 1-OHP concentrations, respectively. The level of statistical significance was set at a = 0.05 for all tests. All data were analysed using SAS v 9.1. RESULTS The kitchen staff averaged 4.1 (SD 2.3) cooking hours in the work place per day. Table 1 compares personal characteristics, work experience and health behaviour between kitchen and service staff. Deep frying, stir frying, grilling, steaming and stewing were the five main cooking methods used by kitchen staff in the surveyed Chinese restaurants. Steaming and stewing were the two main cooking methods used by both kitchen and service staff when cooking at home. There were no significant differences in height, weight, BMI, smoking, number of cigarettes smoked per day, or exposure to second-hand smoke between the kitchen and service staff. None of the 288 restaurant workers wore respiratory protection devices (eg, masks) during the work period. Table 2 lists particulate PAH levels in the kitchens and dining areas of 19 Chinese restaurants. The median levels of pyrene, benzo(k)fluroranhene, benzo(a)pyrene, benzo(ghi)perylene and dibenzo(a,e)pyrene in the kitchens were significantly higher than those in the dining areas. The median levels of summed PAHs in the kitchens were also significantly higher than those in the dining areas. Table 3 lists urinary MDA and 1-OHP levels together with smoking status and job title. All kitchen staff had urinary MDA levels and 1-OHP levels significantly higher than those of service staff. For the non-smoking kitchen staff, mean MDA and Table 4 Multiple linear regression analysis: predictors of urinary 1- hydroxypyrene and malondialdehyde levels in 154 non-smoking restaurant workers Predictors Work in kitchens (kitchen vs service staff) Cooking at home (yes vs no) Second-hand smoke exposure (yes vs no) Work years (years) Work days per week (days) Work hours per day (hours) Age (years) BMI (kg/m2) Log10 1-OHP (mmol/mol creatinine) 1-OHP, 1-hydroxypyrene; MDA, malondialdehyde. *p,0.05; **p,0.001. 734 Log10 1-OHP (mmol/mol creatinine) Regression coefficient (95% CI) Log10 MDA (mmol/mol creatinine) Regression coefficient (95% CI) 0.494 (0.160 to 0.827)* 0.090 (20.022 to 0.203) 0.34 (20.238 to 0.507) 0.034 (20.087 to 0.156) 0.185 (20.128 to 0.497) 0.082 (20.020 to 0.185) 0.016 (20.002 to 0.034) 0.003 (20.001 to 0.009) 0.484 (20.003 to 0.971) 0.005 (20.157 to 0.166) 0.068 (20.003 to 0.138) 0.025 (0.001 to 0.048)* 20.002 (20.019 to 0.015) ,0.001 (20.006 to 0.005) 20.007 (20.053 to 0.039) ,0.001 (20.016 to 0.014) – 0.065 (0.032 to 0.111)** 1-OHP levels were 344.2 (SD 243.7) and 6.0 (SD 8.0) mmol/mol creatinine, respectively, and thus were significantly higher than for non-smoking service staff, which were 244.2 (SD 164.4) and 2.4 (SD 4.3) mmol/mol creatinine, respectively. Urinary MDA levels in smoking kitchen staff remained significantly higher than those in service staff. However, urinary 1-OHP levels in smokers did not differ significantly between kitchen and service staff. Table 4 lists the results of multiple linear regression analysis for urinary 1-OHP and MDA in non-smoking restaurant workers. Kitchen work was found to be a significant and positive predictor of urinary 1-OHP levels after adjusting for other covariates. Kitchen staff urinary 1-OHP levels were increased compared to those of service staff. Work years, work days per week and work hours per day were all marginally significant predictors of urinary 1-OHP (0.05,p,0.1). Cooking at home, second-hand smoke, age and BMI were not significant predictors of urinary 1-OHP levels for restaurant workers. Table 4 also lists predictors of urinary MDA levels for restaurant workers based on multiple linear regression analyses. This study found urinary excretion of 1-OHP and work hours per day to be the main predictors of MDA in urine for all workers after controlling for other covariates. An increase in urinary 1-OHP was associated with an increase in urinary MDA (p,0.001) and an increase in work hours per day was also associated with an increase in urinary MDA (p,0.05). Notably, work in kitchens was not a significant predictor of urinary MDA and work hours per day did not significantly predict urinary 1-OHP. DISCUSSION The high particulate PAH levels in Chinese restaurants demonstrated that kitchen staff have high exposure and service staff low exposure to COF. Since restaurant workers did not wear respiratory protection devices while working, they were at high risk of PAH exposure from COFs. This study used urinary MDA as a biomarker of oxidative stress, and urinary 1-OHP and work experience as indicators of COF exposure to study the impact of COFs on oxidative stress in Chinese restaurant workers. The linear multiple regression models were used to analyse non-smokers only owing to the strong effects of cigarette smoking on PAH uptake. Cigarette smoking influences urinary 1-OHP levels in restaurant workers, a finding which is consistent with a previous study on urinary 1-OHP in asphalt paving workers.25 Cooking at home is not a significant predictor of urinary 1-OHP levels. Cooking methods frequently used in restaurant kitchens included deep frying, stir frying and grilling, all of which generate significant quantities of COFs.8 26 In contrast, steaming and stewing (neither of which generate significant amounts of COFs) were the main cooking methods used at home by restaurant workers, perhaps because Occup Environ Med 2008;65:732–735. doi:10.1136/oem.2007.036970