A systematic review of 68 studies found that vitamin D supplementation (1,000-2,000 IU/day for 1-3 months) increases cathelicidin antimicrobial peptide expression and reduces Staphylococcus aureus colonization and eczema severity in people with vitamin D deficiency.
1,000-2,000 IU/day vitamin D boosts cathelicidinIn VD-deficient eczema patients, supplementation for 1-3 months increased antimicrobial peptide expression, reduced S. aureus, and improved disease severity
What the researchers found
The systematic review of 68 peer-reviewed papers established two key findings:
1. Cathelicidin plays a dual role in atopic dermatitis — it contributes to skin barrier function and has direct anti-Staphylococcus aureus activity. Reduced cathelicidin expression in AD patients weakens both defenses.
2. Vitamin D supplementation at 1,000-2,000 IU/day for 1-3 months increases cathelicidin expression and reduces S. aureus abundance and AD severity — but only in individuals with low serum vitamin D (deficiency/insufficiency). There was no evidence supporting supplementation in people with sufficient vitamin D levels.
Why it matters
Atopic dermatitis affects up to 20% of children and 10% of adults, and S. aureus skin infections are a major complication causing disease flares. Current treatment relies on topical steroids and immunosuppressants, which have side effects with long-term use. The cathelicidin-vitamin D connection offers a natural, low-cost intervention: simply correcting vitamin D deficiency can boost the body's own antimicrobial peptide defense, reducing infections and eczema severity. This represents a mechanistic, nutrition-based approach to managing a common chronic condition.
How the study worked
Systematic literature search following established protocols, with 68 peer-reviewed papers accepted for inclusion. Studies were critically appraised and synthesized in a narrative analysis. The review examined three interconnected relationships: cathelicidin's role in skin barrier function, cathelicidin's anti-S. aureus activity, and vitamin D's ability to upregulate cathelicidin expression in the context of atopic dermatitis.
What this study cannot tell us
The review is a narrative synthesis rather than a formal meta-analysis, limiting quantitative conclusions. Most vitamin D supplementation studies in AD are small and heterogeneous in design. The benefit is limited to vitamin D-deficient/insufficient individuals, and many studies didn't stratify by baseline vitamin D status. Optimal dosing and duration beyond the identified 1,000-2,000 IU/day for 1-3 months range are not established. The causal chain (low VD → low cathelicidin → worse AD) is well-supported mechanistically but not definitively proven in clinical trials.
How to read the evidence
This is a systematic review synthesizing 68 peer-reviewed studies with critical appraisal. While not a formal meta-analysis, the consistent findings across multiple study types support the vitamin D-cathelicidin-AD connection. The evidence for supplementation benefits is strongest for VD-deficient populations.
When this study was published
Published in 2025, this is a current review capturing the latest evidence on the vitamin D-cathelicidin axis in atopic dermatitis, including recent clinical trial data.
The bigger picture
This review connects three major areas: antimicrobial peptide biology, nutritional medicine, and dermatology. The vitamin D-cathelicidin axis is one of the best-characterized examples of how a nutrient directly regulates antimicrobial peptide expression — vitamin D literally turns on the cathelicidin gene. Understanding this mechanism has implications beyond eczema: it may explain why vitamin D deficiency is associated with increased susceptibility to respiratory infections, wound healing problems, and other conditions where antimicrobial peptides play protective roles.
Questions still open
- Would higher vitamin D doses produce greater cathelicidin induction and better eczema outcomes in severely deficient patients?
- Could topical vitamin D application directly boost cathelicidin in the skin more effectively than oral supplementation?
- Does the vitamin D-cathelicidin mechanism explain the seasonal variation in eczema severity?
Common questions
What is cathelicidin and how does it protect the skin?
Should I take vitamin D for my eczema?
Read the original research
Cathelicidin expression in the pathogenesis of atopic dermatitis and the therapeutic potential of vitamin D.
Nutrition research (New York, N.Y.), 139, 113-123
Citation
Connell, Tess; Seidler, Karin; Neil, James. (2025). Cathelicidin expression in the pathogenesis of atopic dermatitis and the therapeutic potential of vitamin D.. Nutrition research (New York, N.Y.), 139, 113-123. https://doi.org/10.1016/j.nutres.2025.05.006