Impact of vitamin D deficiency on 6-month culture conversion in nontuberculous mycobacterial pulmonary disease

Vitamin D modulates antimycobacterial immunity, and its deficiency has been implicated in susceptibility to nontuberculous mycobacterial pulmonary disease (NTM-PD). However, whether baseline vitamin D status influences treatment outcomes remains unclear. We analyzed 485 patients with available baseline serum 25-hydroxyvitamin D [25(OH)D] levels and 6-month culture data from a prospective multicenter cohort (NTM-KOREA) enrolled between April 2022 and August 2025. Vitamin D deficiency was defined as 25(OH)D < 20 ng/mL. The mean age was 64.0 years, 73.2% were female, and 99 (20.4%) had vitamin D deficiency. The overall 6-month culture conversion rate was 44.9%, with no significant difference between deficient and non-deficient groups (42.4% vs. 45.6%; p = 0.651). In multivariable logistic regression, vitamin D deficiency was not associated with culture conversion (adjusted odds ratio [aOR] 1.091; 95% CI 0.662-1.797; p = 0.733), whereas guideline-based treatment showed a strong positive association (aOR 3.781; 95% CI 1.825-7.832; p < 0.001). Multivariable Cox regression confirmed no association between vitamin D deficiency and time to conversion (adjusted hazard ratio 1.031; 95% CI 0.721-1.475; p = 0.868). Baseline vitamin D deficiency was not independently associated with 6-month culture conversion or time to conversion in treated NTM-PD patients.