Participants and procedure
We carried out a participatory workplace improvement intervention [13–22] from August 2017 to February 2018. Briefly, the participatory workplace improvement intervention is that employees at the workplace actively take part in identifying workplace problems, find feasible actions/solutions, and work towards improvement. We recruited nurses (n = 144) working at a hospital with 150 beds in the southern part of Japan. A total of 36 nurses agreed to participate in this study. We conducted evaluations before the intervention for baseline (T1), within a week after the end of the intervention to assess immediate effects (T2), and 3 months after the end of the intervention to assess prolonged and lasting effects (T3). We excluded participants who became pregnant during the study period (n = 1), missed evaluations (n = 3) and had incomplete responses in giving social support scores (n = 1). A male participant (n = 1) was also excluded because of possible sex differences in outcome measures. Therefore, a total of 30 female nurses were submitted to the final analysis.
Sociodemographic, lifestyle, health, and occupational conditions
We used the self-administered questionnaire to assess participants’ sociodemographic and job-related characteristics including social support at work and perceived psychosocial job stress.
Giving social support
In the questionnaire, we included questions of ‘giving’ social support to others at work, which we modified from ‘receiving’ social support in the Brief Job Stress Questionnaire ; “How much help do you provide to the following people?”, “How much are you relied on by the following people?”, “How well do you listen to the following people when they ask for advice on personal matters?”. Participants answered each question by “superiors”, “co-workers”, and “subordinates” with a four-point scale (1 = extremely to 4 = not at all). Cronbach’s alphas for these items were > 0.630 at all-time points.
We used serum interferon (IFN)-γ, interleukin (IL)-6, tumor necrosis factor (TNF)-α, IL-12/23p40, IL-15, IL-27, and high-sensitivity C-reactive protein (hs-CRP) as inflammatory markers. On the evaluation days, participants (nurses) brought their blood samples which collected between 2 pm and 5 pm in gamma-rays sterilized polyethylene-terephthalate tubes containing serum separating gel and coagulation accelerant (silica particles). We stored the samples in a cooler box (0–5°C) and transported them to our laboratory twice a day by 4:30 pm and 7:30 pm. In the laboratory, we centrifugalized them with 2,400 rpm for 10 minutes to extract 500µL of the serum and deep-freezed (-20°C) until the analysis. The level of inflammatory markers was assessed with the Enzyme Immunoassay or Chemiluminescent Enzyme Immunoassay with MESOTM QuickPlex SQ 120 (Meso Scale Diagnostic, LCC, Rockville, USA) by the analyzing company, Life Science Institute Medience Corporation, Japan. The minimum detectable level for IFN-γ, IL-6, TNF-α, IL-12/23p40, IL-15, IL-27, and hs-CRP was 0.2 pg/ml, 0.06 pg/ml, 0.04 pg/ml, 15.0 pg/ml, 2.0 pg/ml, 8 pg/ml, and 0.004 mg/dl, respectively. We calculated the values lower than them into the minimum detectable level/√2, as it was described elsewhere .
Autonomic nervous activity (ANA)- Heart rate variability (HRV)
We utilized an electrocardiograph device, Silmee Bar Type Lite (Silmee; Tokyo Denki Kagaku, Tokyo, Japan) to measure heart rate variability (HRV). Silmee automatically calculates HRV by the power spectral analysis and measures 3 sympathetic nervous activity (SNA); low-frequency HRV/total frequency HRV (standing position), mean R-R interval/R-R interval per minute (standing position), and mean R-R interval (supine-stand position), and 3 parasympathetic nervous activity (PNA) parameters; mean R-R interval (supine position), high-frequency HRV/total frequency HRV (supine position), and the standard deviation of R-R intervals (SDRR) (supine position). Silmee also calculates SNA/PNA. We measured participants’ autonomic nervous activities in two rooms at the hospital between 2 pm and 5 pm to adjust in-day fluctuation.
Based on the total giving social support score at each time-point, we divided participants into two groups; those who had increased scores on giving social support to others after the intervention (Group 1, n = 13), and those who had decreased/unchanged in the scores (Group 2, n = 17). After the confirmation of non-Gaussian distribution with the Shapiro-Wilk test, we applied the Friedman test to examine changes in inflammatory markers, autonomic nervous activity, and perceived job stress by the group. We analyzed data using IBM SPSS Statistics for Windows, version 25.0 (IBM Corp., Chicago, IL, USA), and the level of significance was set at p < 0.05.