Background: This study aims to synthesize the evidence from randomized controlled trials of micronutrient supplementation to prevent and treat acute respiratory infections in adults. The study evaluated the effectiveness of micronutrient supplementation in preventing acute respiratory infections (ARIs) and reducing the duration of ARIs. 

Methods: PRISMA guidelines were followed for the search of the literature. The relevant studies were identified and selected.  A pooled estimate for exposure-outcome relationships reported by four or more studies was measured. Random-effects meta-analysis based on the maximum probability was conductedto estimate the pooled effects of vitamin D, vitamin C, zinc, and multiple micronutrient supplementation on the occurrence of ARIs and the duration of ARI symptoms.

Results: The results showed that vitamin D supplementation reduced the risk of ARI (risk ratio (RR) =0.97; 95% CI 0.94 to 1.00; p=0.028) and shortened the duration of symptoms (per cent difference: -6% (95% CI-9% to -2%; p=0.003). Vitamin C supplementation reduced the risk of ARIs (RR=0.96; 95% CI 0.93 to 0.99; p=0.01) and shortened the duration of symptoms (per cent difference: -9% (95% CI-16% to -2%; p=0.014). Zinc supplementation did not reduce the risk of ARIs but shortened the duration of symptoms substantially (per cent difference: -47% (95% CI-73% to-21%; p=0.0004). 

Study inference: The study concluded that micronutrient supplements including zinc, vitamins C and D, and multiple micronutrient supplements might be modestly effective in preventing ARIs and improving the clinical course of the disease. 

Study highlights: Micronutrient supplementation may prevent (vitamin D and C) and treat (Vitamin D, C, and zinc) for ARIs, including SARS-CoV-2 infection. Vitamin D supplementation shortens the duration of ARI symptoms mildly. The preventive effect of vitamin C against ARIs is more among men and residents of middle-income countries. 

Reference: Abioye AI, Bromage S, Fawzi W. BMJ Global Health. 2021; 6: e003176.