Clinical Efficacy of Probiotics for Relieving Cold Symptoms in Healthy Individuals: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

Abstract

Background: Colds are widespread infectious diseases that affect daily life, increasing healthcare costs and limiting productivity. Objectives: The aim of this study was to investigate the effects of a dietary supplement containing specific probiotic strains (L. plantarum PBS067, L. acidophilus PBS066, B. lactis BL050) on cold symptom relief, immune response enhancement, and quality of life. Methods This randomized, double-blind, placebo-controlled trial included 65 healthy volunteers (age range: 18-44 years), divided into two groups: 40 received the probiotic treatment (with vitamins and bulking agents), and 25 received placebo (vitamins and bulking agents only) for 12 weeks. Cold symptoms and systemic inflammation were assessed at three time points (baseline T0, post-treatment T1, and 6 weeks after treatment T2). Results: Probiotics were associated with a shorter average duration of cold symptoms (4.5 vs. 6.7% for Placebo, p < 0.05). At T1, fever and muscle pain occurred in 20% of participants in the Probiotic group vs. 28% and 44% in the Placebo group, respectively (p < 0.05 for muscle pain vs. Placebo). For muscle pain, a trend was maintained also at T2 (17.5% vs. 20%). The pro-inflammatory cytokine IFN-γ levels significantly decreased in the Probiotic group vs. T0 (p < 0.0001 at T1 and p < 0.01 at T2), while they increased in the Placebo group (22.279 ± 3.538 vs. 19.432 ± 3.143 pg/mL, p = NS). Although not statistically significant, at T1 the Probiotic group had higher levels of IL-10 vs. T0 (266.98 ± 78.432 vs. 240.967 ± 70.238, pg/mL p = NS). Conclusions: The probiotic mix effectively alleviated cold symptoms and reduced pro-inflammatory cytokine levels, suggesting anti-inflammatory effects.

Keywords: URTIs; cold symptoms; food supplements; immunity; probiotics.

Figure 1

Study timeline. Seventy-five healthy volunteers aged 18–44 were recruited and screened during winter in the years 2022–2024 (16 subjects were recruited and screened in December 2022, 20 January 2023, 26 December 2023, 13 January 2024, respectively). Ten participants dropped out of the study (6 for personal reasons and 4 for antibiotic use).

Figure 2

Flowchart of the study.

Figure 3

WURSS-21 questionnaire results in subjects randomized to the Probiotic and Placebo groups. The probiotic group showed a significant reduction in cold symptoms at both T1 and T2 compared to baseline values (* p < 0.05). Conversely, the Placebo group reported a rise in the severity of cold symptoms at T1 and T2 compared to T0.

Figure 4

The average percentage of days in which subjects experienced cold symptoms in Probiotic and Placebo groups at T1 and T2, respectively. Chi-squared test was applied. *** p < 0.001.

Figure 5

Percentage of subjects presenting fever (a) and muscle pain (b) symptoms in Probiotic and Placebo groups at T1 and T2, respectively. A chi-squared test was applied. * p < 0.05.

Figure 6

Percentage of subjects who needed treatment for cold (a) and without any symptom of cold (b) in Probiotic and Placebo groups throughout the study period.

Figure 7

(a) IFN-γ and (b) IL-10 total cytokine dosages at each time point considered in the study. Data are reported as mean ± SEM. Two-way ANOVA followed by Dunnett’s multiple comparisons test was applied. ** p < 0.01; **** p < 0.0001.