Study  Author  Study Population  Micronutrient (Dosage)  Results
The effect of vitamin C on upper respiratory infections in adolescents swimmers: a randomized trial.  Constantini NV 2011 [68]  Children (12–17 years)RCT  Vitamin C (1 g/day for 3 months)  In the male swimmers duration (p = 0.003) and severity (p = 0.003) of URTI episodes were decreased.
Vitamin C for preventing and treating the common cold.  Hemilä H 2013 [67]  Adults and children31 RCTs  Vitamin C (>0.2 g/day)  Significant reduction in the duration of common cold episodes. Decreased cold severity in Vitamin C group.
Vitamin C for preventing and treating pneumonia.  Hemilä H 2013 [65]  Adults3 RCTs  Vitamin C  Significant reduction in pneumonia risk (>80%). Lower mortality in the vitamin C group vs. placebo group.
Vitamin C supplementation slightly improves physical activity levels and reduces cold incidence in men with marginal vitamin C status: a randomized controlled trial.  Schumacher SS 2014 [66]  AdultsRCT  Vitamin C (1 g/day for 8 weeks)  Reduced cold episodes in young men with low to average vitamin C status (p = 0.04). Cold duration was reduced 59% in the vitamin C vs. placebo groups (p = 0.06).
Probiotics and vitamin C for the prevention of respiratory tract infections in children attending preschool: a randomised controlled pilot study.  Ďuračková Z 2015 [69]  ChildrenRCT  Vitamin C (50 mg/day for 6 months)  Reduced incidence (p = 0.002) and duration (p = 0.006) of URTIs. No significant differences in the duration or incidence of LRTIs.
Extra dose of vitamin C based on a daily supplementation shortens the common cold: a meta-analysis of 9 randomized controlled trials.  Ran L 2018 [70]  Adults and children9 RCTs  Vitamin C (4–8 g/day)administrated at the onset of cold  Reduced cold duration (MD = −0.56, p = 0.02). Relieved cold symptoms including chest pain (MD = −0.40, p = 0.03), fever (MD = −0.45, p = 0.009), and chills (MD = −0.36, p = 0.01).
Effect of vitamin C infusion on organ failure and biomarkers of inflammation and vascular injury in patients with sepsis and severe acute respiratory failure: the CITRIS-ALI randomized clinical trial.  Fowler AA 2019 [72]  AdultsRCT  Vitamin C (IV 50 mg/kg every 6 h for 96 h)  Significant reduction in 28-day all-cause mortality (p = 0.03), and with significantly increased ICU-free days to day 28 (p = 0.03) and hospital-free days to day 60 (p = 0.04).