Additionally, we calculated the intensity of the work performed on night shifts during the whole work period. Blood samples were collected between 06:00 and 10:00 a.m from each participant into S-Monovette® test tubes with lithium heparin as anticoagulant.

In JIB04 the case of night shift workers, blood collection was synchronized with the night shift, and the blood samples were collected at the end of night shift. Glutathione peroxidase activity (GSH-Px) was determined by the method of Paglia and Valentine (1967) with t-butyl hydroperoxide as substrate. Superoxide dismutase (SOD) was assayed with the use of the method based on the inhibition of reduction of nitroblue tetrazolium in the presence check details of xanthine and xanthine oxidase (Beauchamp and Fridovich 1971). Lipid peroxidation was estimated from the this website measurements of TBARS levels in plasma using the method modified by Wasowicz et al. (1993). The plasma selenium concentration was determined by graphite furnace atomic absorption spectrometry (GFAAS) (Neve 1991). The method was validated using the reference material (lyophilized human reference serum samples of Seronorm from Nycomed

Pharma AS, Oslo, Norway) and through participation in the interlaboratory comparison trials. Vitamin E and A levels were determined by the HPLC system integrated with UV–VIS detector range 190–800 nm (Grzelinska et al. 2007). Statistical analysis The data from the biochemical analyses was expressed as a mean and a standard deviation. Characteristics of the study groups were compared using the Pearson’s chi-squared test and the Student’s t test. Linear regression model was PD184352 (CI-1040) used to analyze the relationship between antioxidants and markers of oxidative stress and night shift work. Multivariate

linear regression was applied to adjust for age, oral contraceptive hormone use, smoking, and drinking alcohol during last 24 h as potential confounders. Following that, the interaction between night shift work and menopausal status was investigated. We used robust linear regression to validate our results against the outliers. STATA 11 software was used to conduct all statistical analyses. Results The characteristics of the studied population comprising nurses and midwives are listed in Table 1. In the investigated group, at the time of the research, 359 nurses worked only daytime and 349 worked currently on rotating night shifts. These two groups differed significantly as for age (p < 0.0001), menopausal status (p < 0.0001), and current smoking habits (p = 0.02). The average total work duration was significantly shorter (27.5 ± 6.6 years) in nurses working currently on rotating night shifts than in day-workers (29.2 ± 6.3 years) (data not shown). The current night shift workers had, however, worked night shifts significantly longer (26.6 vs. 12.4 years).