Top 7 Evidence-Based Recommendations

Dissolving lozenges flood the oropharynx with free Zn2+ that interferes with rhinovirus replication and prevents viral docking; acids like citric acid bind zinc and kill this effect. ^[2][20][21]

IPD/meta-analyses of RCTs show ~30–40% shorter cold duration with properly formulated lozenges providing ≥75–80 mg/day elemental zinc, with similar benefit for acetate and well-formulated gluconate. Poorly formulated lozenges fail. ^{[2][3][4][22]}

Andrographolides modulate innate and adaptive immunity (e.g., cytokine balance) and appear to blunt URTI symptom intensity. ^[5][10]

Systematic reviews and RCTs (including modern standardized extracts) show faster symptom resolution vs. placebo in uncomplicated URTI; some prevention data over winter months. Mixed results in recent respiratory viral trials, but URTI symptom data are positive. ^{[5][8][9][11][12]}

Strain-specific effects on mucosal immunity (e.g., IgA), barrier integrity, and antiviral signaling reduce URTI incidence and sick days. ^[13][14][16]

Cochrane 2022 and adult RCT meta-analyses show reduced URTI incidence and duration versus placebo, though heterogeneity is high; effects are strain- and regimen-dependent. ^[13][16]

Calcitriol enhances antimicrobial peptides and tempers excessive inflammation; effects depend on baseline deficiency and dosing schedule. ^[1][6]

Earlier IPD meta-analyses found modest protection, especially with daily/weekly dosing and low baseline 25(OH)D. A 2025 Lancet Diabetes & Endocrinology update, adding new large RCTs, found the overall effect crossed null—benefit, if any, is small and context-dependent. ^[1][6][7]

Replenishes glutathione and modulates inflammatory signaling, reducing progression to symptomatic illness despite similar infection rates. ^[17][29]

A 6-month RCT (n=262; mostly ≥65 y) showed markedly fewer and milder influenza-like illnesses vs. placebo. Animal and mechanistic data support synergy with antivirals; human URTI evidence centers on older/high-risk populations. ^{[17][25][26][28][29]}

Primes neutrophils and macrophages via dectin-1/CR3 to improve first-response defenses and symptom control. ^[30]

Randomized trials in marathoners show fewer symptomatic days and lower severity (especially with insoluble forms). Evidence is strongest in physically stressed cohorts; modest effects overall. ^[23][30]

Supports leukocyte function and redox balance; reduces severe-symptom days more than mild ones. ^[31][32]

Cochrane shows no prevention in the general public, but ~8% shorter duration (bigger in kids/athletes) and ~50% prevention in ultra-stress cohorts; recent analyses suggest greater reduction in severe symptoms. ^[31][32]