People with active lung TB often have low vitamin D levels, but their blood levels of the antimicrobial peptide LL‑37 don’t seem to depend on vitamin D. Higher LL‑37 was linked to more bacteria in sputum and being underweight, not to better vitamin D status.

Vitamin D insufficiency is common in industrialized and developing nations. Recent studies have shown that vitamin D insufficiency is associated with a higher risk of active tuberculosis. Laboratory studies provided a mechanism for this link on the basis of findings that vitamin D metabolites regulate the expression of cathelicidin (LL-37), which is an endogenous antimicrobial peptide with activity against Mycobacterium tuberculosis. Little information is available on the clinical relation between vitamin D, LL-37 concentrations, and disease severity in patients with tuberculosis. The primary objective of the study was to evaluate the relation between vitamin D nutriture, serum LL-37 concentrations, and tuberculosis by using samples stored in the Tuberculosis Trials Consortium serum repository. We measured 25-hydroxyvitamin D [25(OH)D] and LL-37 concentrations in 95 serum specimens from patients with culture-confirmed pulmonary tuberculosis and correlated these concentrations to clinical and demographic variables. The prevalence of vitamin D insufficiency [serum 25(OH)D concentration lt 30 ng/mL] in patients with active tuberculosis was 86% (n = 95) with a mean baseline serum 25(OH)D concentration of 20.4 ng/mL. Factors associated with vitamin D insufficiency were black race and indoor lifestyle. The mean ( plusmn SD) baseline LL-37 concentration was 49.5 plusmn 23.8 ng/mL. Higher LL-37 concentrations correlated with acid fast bacilli sputum smear positivity and weight gt 10% below ideal body weight. Serum vitamin D status of the study subjects did not correlate with serum LL-37 concentrations. More prospectively designed studies are needed to evaluate the clinical implications of vitamin D insufficiency in patients with tuberculosis and the utility of circulating LL-37 as a potential biomarker in patients with active tuberculosis disease. The parent trial was registered at clinicaltrials.gov as NCT00023335.