This trial was conducted between November 2020 and December 2020 at Hebei Medical University, Shijiazhuang, China. Our pre-study result showed an 11% difference in FVC between groups. To detect this difference with 90% power at a significance level (alpha) of 0.05 required 58 participants. Allowing for 20% dropout, 70 participants were required. The participants were recruited according to the following criteria: 1) residing locally or on the campus within 2 months of the start of the trial; 2) aged 18–26 years; 3) no history of chronic cardiopulmonary disease (such as chronic obstructive pulmonary disease, asthma, or other systemic disease), smoking, or toxic chemical exposure; 4) capable of participating in daily activities; and 5) willing to provide biological specimens and informed consent and cooperate with the researcher during the entire study period.

This study was a randomized, double-blind, placebo-controlled trial. All participants were randomly divided into the QJWJ and placebo groups. All participants took QJWJ or placebo granules twice daily for 4 weeks from November 21 to 20 December 2020. We conducted one baseline examination and two rounds of follow-up visits, with intervals of 2 weeks. At baseline and follow-up, we collected fasting blood samples and measured RVD, lung function, heart rate, respiration rate, and blood pressure. At the end of the trial, the induced sputum was tested for inflammatory cells. Additionally, individual characteristics (height and weight) were recorded at baseline and follow-up. Volunteers, researchers, and data collection staff were blinded to the allocation.

This study was approved by the Ethics Committee of Hebei Medical University and registered in the Chinese Clinical Trial Registry (ChiCTR2000039210). All participants provided written informed consent on enrollment.

The QJWJ and placebo granules were produced by Zhejiang Yalin Biological Technology Co., Ltd. China. The QJWJ granules contained four medicinal herbs extracted and purified from 12 g of Phragmites australis (Cav.) Trin. ex Steud [Poaceae], 6 g of Coix lacryma-jobi var. ma-yuen (Rom.Caill.) Stapf [Poaceae], 4.5 g of Prunus persica (L.) Batsch [Rosaceae], and 6 g of Benincasa hispida (Thunb.) Cogn [Cucurbitaceae]. In contrast, the placebo was composed of dextrin and caramel and was identical to QJWJ in color, shape, size, and packaging. Participants were instructed to take two packages of QJWJ, or placebo, dissolved in water per day throughout the study period. They were also asked to complete two questionnaires to determine compliance, on the day before both follow-ups. Meanwhile, the staff created several instant messaging groups to remind participants to consume the granules throughout the study period.

QJWJ granules were dissolved in purified water at the concentration of 100 mg/ml. The solution was then centrifuged for the supernatant. The UPLC analyses of QJWJ solution supernatant was performed using the 2.1 × 100 mm reversed-phase C18 analytical columns with 1.6 μm silica-based (Cortecs® UPLC® T3, waters, SYNAPT G2-Si, US). The mobile phase was composed of solvent A 10% (formic acid at 0.1%) and solvent B 90% (acetonitrile). The injection volume was 2 µl in each run with a flow rate of 0.3 ml/min and a gradient elution of 35 min: 0–2 min, 5% B; 2–32 min, 5–100% B; 32–33 min, 100% B; 33–35, 5% B. MS spectra were acquired in positive-ion mode (Tricin) and negative-ion mode (Coixol, Asperglaucide, and Amygdalin). The Q-TOF/MS was operated with capillary voltage 2.5 kV (negative ion) and 3 kV (positive ion), sample cone voltages 40 V, source temperature 120°C, desolvation temperature 500°C, desolvation gas flow of 1000 L/h, collision energy of 6 eV, full scan spectra from 50 to 1200 Da.

Blood pressure and heart rate were measured using an electronic sphygmomanometer (Omron J710, Japan). Fasting peripheral blood samples were collected in vacuum tubes between 8:00 and 9:00 a.m. A noninvasive pulmonary function test was performed using a portable pulmonary function testing machine (MSA99, Beijing M&B Electronic Instruments Co., Ltd. China). Lung function measurements included the vital capacity (VC), FVC, FEV_1.0, peak expiratory flow (PEF), MMEF, and forced expiratory flow between 25 and 75% of the FVC (FEF₂₅, FEF₅₀, FEF₇₅). The lung function parameter values were expressed as percent predicted using the estimated prediction value. RVD was defined as FVC <80% predicted and FEV_1.0/FVC ≥0.70 (Kim et al., 2015). Two certified nurses completed all the clinical examinations at the university hospital. In addition, we collected data on key individual characteristics, including height and weight at baseline and during the follow-ups, and the body mass index (BMI) was then calculated. All measurements were performed in a quiet room. Induced sputum was collected and processed as described by Pavord (Pavord et al., 1997). The GIMAS dying assay (Baso Diagnostics Inc. Zhuhai, China) was used to ascertain the proportion of lung inflammatory cells (monocyte-macrophages, neutrophils, eosinophils, and lymphocytes) in the induced sputum. We counted at least 200 lung inflammatory cells under an oil microscope and calculated the percentage of all cell types.

We obtained real-time concentrations of ambient PM_2.5 using the AirCasting Air Monitor (New York Hall of Science, USA), a portable personal environmental dust monitor. All devices were calibrated externally through an aerosol monitoring meter (pDR-1500, Thermal Scientific, China), and the following equation was used to calculate the PM_2.5 concentrations: F o r m u l a : Y = 10^ ( I n t e r c e p t + S l o p e ∗ log ( X ) ) (1) X refers to the concentration of the portable monitor, while Y refers to the ambient PM_2.5 concentrations. The fitting degree of R ² was between 0.97 and 0.98 in this model (Supplementary Table S1; Supplementary Figure S1 in the Supplementary Appendix S1).

Each monitor was distributed to every four or six participants who lived in the same dormitory and had similar activities throughout the study. The participants were required to carry the data monitor from 8:00 a.m. to 8:00 p.m. every day.

The distribution of the lung function parameters and PM_2.5 concentrations were tested using the Kolmogorov–Smirnov test. The variables with normal and non-normal distributions were calculated and described as mean ± standard deviation (SD) and median (interquartile range), respectively. Pearson’s chi-square test and the t-test were used to assess the differences between the placebo and QJWJ groups. To test the correlation between PM_2.5 and lung function, Pearson’s correlation coefficient (Pearson’s r) was calculated. To derive the potential lagged effects of PM_2.5 on lung function, multiple averaging periods were applied preceding the lung function measured, that is, lag 0 weeks (7 days before examination day), lag 1 week (from the eighth to the 14th day before examination), and lag 0–1 week (14 days before the examination day). In all analyses, statistical significance was set at two-tailed P-values < 0.05.

A total of 70 participants were screened, and 66 were enrolled and underwent randomization (33 were assigned to the QJWJ group, and 33 were assigned to the placebo group). One participant was excluded because no biological specimens were provided at the beginning of the study. Sixty-five participants (32 from the QJWJ group and 33 from the placebo group) completed the scheduled follow-ups (Figure 1). The height, weight, BMI, body temperature, heart rate, blood pressure, systolic blood pressure, and diastolic blood pressure did not differ between the two groups at baseline (Table 1). Routine blood test markers were analyzed in each health examination to evaluate the safety of QJWJ, and there was no statistically significant difference in blood biomarkers between the two groups at baseline or at the end of the trial (Supplementary Table S2 in the Supplementary Appendix S1).

Figure 2 shows the concentration of PM_2.5 at different periods of the study. The participants’ average concentration of PM_2.5 exposure was 63.49 ± 44.08 μg/m³, slightly lower than the level of the monitoring site (80.17 ± 47.13 μg/m³). There was no significant difference in the daily and weekly averages of PM_2.5 between the two groups during the study period (Figures 2A,B). The average exposure concentration of PM_2.5 at lag 0 weeks was 79.71 ± 15.47 μg/m³, 86.46 ± 15.99 μg/m³ at lag 1 week, and 82.82 ± 14.66 μg/m³ at lag 0–1 week (Supplementary Table S3).

To demonstrate the major components of QJWJ granules, the UPLC-Q-TOF/MS analysis was performed and the total HPLC profile of QJWJ attained was shown in Supplementary Figure S2–S5. According to MS spectrum and retention times of UPLC-Q-TOF/MS analysis, peaks of QJWJ were tentatively identified as Coixol (Supplementary Figure S2), Asperglaucide (Supplementary Figure S3), and Amygdalin (Supplementary Figure S4) in negative ion mode, Tricin (Supplementary Figure S5) in positive ion mode. Taken together, the major chemical active components of QJWJ were Coixol, Asperglaucide, Amygdalin, and Tricinj, which were consistent with previous studies (Gao et al., 2009; Fan et al., 2015; Wang et al., 2020; Li et al., 2021).

We collected the data on the prevalence of RVD in different countries from the literature. The BOLD study reported that the incidence of RVD is 16.4% worldwide (Mannino et al., 2012). It varied widely across different countries, ranging between 8.5 and 46.1% (Soriano et al., 2012; Lee et al., 2015; Godfrey and Jankowich, 2016). Our study found that the incidence of RVD was 23.1% among the participants (Figure 3A). We also found a positive correlation between the global national annual mean PM_2.5 concentration and the incidence of RVD (Figure 3B).

The proportion of RVD was 21% in the placebo group and 25% in the QJWJ group at baseline. There were no other differences between the two groups. The percentage decreased to 6.2% after QJWJ administration for 2 weeks. Moreover, The RVD of all the participants returned to normal at the end of the QJWJ intervention, which was significantly different from the placebo group (P = 0.018) (Table 2).

Lung function was primarily examined by VC, FVC, FEV_1.0, MMEF, PEF, FEF₂₅, FEF₅₀, and FEF₇₅. VC, PEF, and FEF₇₅, but not other indexes, were negatively correlated with PM_2.5 exposure at lag 0 weeks before the intervention. VC, FEV_1.0, PEF, FEF_75, and FEF₅₀ were negatively correlated with PM_2.5 exposure at lag 1 week before the intervention. However, the significantly negative correlation between lung function parameters and PM_2.5 exposure concentrations diminished at different time points after 2 and 4 weeks of QJWJ intervention (Table 3).

We compared the levels of the lung function parameters between the two groups. No lung function parameter was significantly different between the QJWJ and placebo groups at either the baseline or follow-up time points. However, compared to the baseline before QJWJ intervention, QJWJ administration significantly increased the FVC and FEV_1.0 at the follow-ups (Table 4).

As showed in Table 5, the proportion of eosinophils in the QJWJ-induced sputum was 1.55%, which was significantly lower than that in the placebo group (2.58%). However, there was no significant difference in the proportions of the monocytes/macrophages, neutrophils, and lymphocytes between the two groups.