Vitamin D (specifically 1,25-dihydroxyvitamin D3) upregulates cathelicidin (LL-37) and defensins — antimicrobial peptides — in macrophages and neutrophils. Lactoferrin independently induces lactoferricin generation from its N-terminal domain. The two antimicrobial peptide pathways are distinct and additive, providing broader pathogen coverage. Both also independently modulate NK cell and T cell activity.

Should I test my vitamin D level before starting this combination?

Testing 25(OH)D level is recommended before supplementing with vitamin D above 2,000 IU/day. Target serum 25(OH)D: 40–60 ng/mL. Adjust vitamin D dose to achieve this range.

Does lactoferrin affect vitamin D metabolism?

No documented effect of lactoferrin on vitamin D metabolism (CYP27B1, CYP24A1). The two can be combined without pharmacokinetic concern.