Association of high serum vitamin D concentrations with active pulmonary TB in an HIV co-endemic setting, Harare, Zimbabwe.

Background: There is paucity data on the association of vitamin D deficiency (VDD) and active tuberculosis (TB) in southern Africa where the human immunodeficiency virus (HIV) is co-endemic. We examined the association of serum vitamin D concentrations with active pulmonary tuberculosis (PTB) in HIV-infected (n = 284) and uninfected (n = 267) Black Zimbabweans, in Harare, Zimbabwe.

Methods: We conducted a cross-sectional study of 551 participants comprising 145 HIV/PTB , 139 HIV/PTB, 134 HIV/PTB and 133 HIV/PTB. PTB status was confirmed using sputum by culture, or smear microscopy, or GeneXpert MTB/RIF. Serum 25-hydroxyvitamin D (25(OH)D) concentrations were measured using a competitive chemiluminescent immunoassay prior to commencement of anti-TB treatment.

Results: In all four groups, the median vitamin D concentrations were above the 20 ng/ml cut off for VDD. However, the median vitamin D concentrations in all the four groups were below the cut off for vitamin D sufficiency ≥30 ng/ml. The median vitamin D concentrations were significantly higher in PTB cases; 24.2 ng/ml (IQR: 18.8-32.0) compared to PTB controls 20.9 ng/ml (IQR: 17.1-26.9), p < 0.0001 regardless of HIV status. The HIV/PTB group had the highest median vitamin D concentration (25.3 (IQR: 18.0-33.7 ng/ml) whilst the HIV/PTB group had the lowest; 20.4 ng/ml (IQR: 14.6-26.9), p = 0.0003. Vitamin D concentration <30 ng/ml was associated with 43% lower odds of being PTB OR 0.57 (95% CI 0.35-0.89).

Conclusions: Our results are not in agreement with the generally accepted hypothesis that VDD is associated with active PTB. To the contrary our results showed an association of higher vitamin D concentrations with active TB irrespective of HIV status. Although findings from the available pool of case control studies remain inconsistent, the results from the current study provide further rationale for larger-scale, prospectively designed studies to evaluate whether sufficient vitamin D concentrations do indeed precede the development of active PTB in our setting.