Evidence supporting the use of: Vitamin D3
For the health condition: Infection (viral)

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Synopsis

Source of validity: Scientific
Rating (out of 5): 3

Vitamin D3 (cholecalciferol) has been investigated for its role in supporting immune function and potentially reducing the risk or severity of viral infections. Several observational studies have found that individuals with low serum vitamin D levels are at increased risk of respiratory tract infections, including those caused by viruses. Mechanistically, vitamin D is known to modulate both innate and adaptive immune responses, enhance the production of antimicrobial peptides (such as cathelicidin), and regulate inflammatory cytokine responses, which may help control viral replication and reduce immunopathology.

Randomized controlled trials (RCTs) and meta-analyses offer moderate support for the use of vitamin D supplementation to prevent certain infections. A 2017 meta-analysis published in BMJ found that vitamin D supplementation reduced the risk of acute respiratory infections, particularly in individuals who were vitamin D deficient. During the COVID-19 pandemic, interest surged in vitamin D’s potential protective effects. While some studies suggested that vitamin D deficiency was associated with increased susceptibility to and worse outcomes from viral infections such as influenza and SARS-CoV-2, results from intervention studies have been mixed, and no conclusive evidence exists that vitamin D3 supplementation alone can prevent or treat viral infections.

Overall, while there is a sound biological rationale and moderate scientific evidence supporting the use of vitamin D3 to help reduce the risk of certain viral infections, it should not be considered a replacement for established preventive or therapeutic measures. Further large-scale, high-quality RCTs are needed.

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