Upper respiratory tract infection (URTI) is the most common illness in humans. Fermented milk containing probiotics can mitigate URTI symptoms.
This study tests the effect of fermented milk (Qingrun), a yogurt supplemented with subsp. Bl-04, on adults with URTIs who live in a haze-covered area in a randomized clinical trial.
A total of 136 subjects were enrolled in the study at the baseline and randomized to consume either control yogurt or Qingrun yogurt (250 g) once daily for 12 weeks. The duration and severity of URTI were evaluated by the Wisconsin Upper Respiratory Symptom Survey-24. Blood and faecal samples were collected at the baseline and post-intervention, to determine the changes of immune biomarkers.
Qingrun yogurt significantly reduced the incidence of the common cold (OR, 0.38; 95% CI, 0.17-0.81;  = 0.013) and influenza-like illness (OR, 0.32; 95% CI, 0.11-0.97;  = 0.045). Compared to the control yogurt, Qingrun yogurt significantly reduced the duration (1.23 ± 2.73 vs. 4.78 ± 5.09 d) and severity score (3.58 ± 7.12 vs. 11.37 ± 11.73) of URTI. In addition, the post-intervention levels of interferon-γ (139.49 ± 59.49 vs. 113.45 ± 65.12 pg/mL) and secretory immunoglobulin A (529.19 ± 91.70 vs. 388.88 ± 53.83 mg/dL) significantly increased in the Qingrun group, compared with those in the control group.
Qingrun yogurt showed a protective effect against URTI in adults, suggesting that the use of yogurt with probiotics could be a promising dietary supplement for mitigating URTI.