Strong evidencevitamin
Vitamin D for Frequent Colds
Vitamin D activates innate immune defenses by inducing cathelicidin and defensin antimicrobial peptides. It also enhances macrophage pathogen killing, modulates T-cell response, and reduces excessive inflammatory cytokine production.
How strong is the research?
Strong evidence
Based on a meta-analysis of multiple studies — the highest level of research evidence.
Research source
SourceMartineau AR et al. · BMJ 2017How much to take
2000–4000 IU
Test 25(OH)D levels. Those with levels <25 ng/mL benefit most from supplementation for immune support.
When to take it
Best taken: morning