Association of circulating serum free bioavailable and total vitamin D with cathelicidin levels among active TB patients and household contacts

Abstract The free hormone hypothesis postulates that the estimation of free circulating 25(OH)D may be a better marker of vitamin D status and is of clinical importance compared to total vitamin D levels because it is the fraction involved in biological activities. Studies have shown that cathelicidin inhibits the growth of Mycobacterium Tuberculosis in a vitamin D-dependent manner and therefore adequate vitamin D is required for its expression. The aim of the study was to determine the association between serum-free and bioavailable and total vitamin D with LL-37 levels in ATB patients, LTBI and individuals with no TB infection. This was a cross sectional study and free and bioavailable vitamin D and LL-37 levels were measured. 95 specimens were further selected to estimate total vitamin D levels. The median free and bioavailable vitamin D levels of study participants were 3.8 ng/mL. The median LL-37 levels were 318.8 ng/mL. The mean total vitamin D levels were 18.9 ng/mL. Significantly weak inverse associations were found and vitamin D is involved in the regulation of LL-37 expression and low vitamin D levels can alter this relationship.