Vitamin D status among pulmonary tuberculosis patients and controls in Tanzania

Vitamin D may be a determinant of tuberculosis (TB)⁽¹⁾, yet the evidence is inconclusive. To assess the role of pulmonary TB (PTB), HIV and acute phase response as predictors of serum 25(OH)D, we conducted a sex- and age-matched cross-sectional study among PTB patients and non-TB controls. The PTB patients were categorised as sputum negative (PTB−) and positive (PTB+) based on culture. For 355 cases, an age- and sex-matched non-TB neighbourhood control was randomly selected. HIV status and serum S-25(OH)D, CRP and AGP were determined. Linear regression analysis was used to assess predictors of S-25(OH)D.

Vitamin D data were available on 97.8% of 1605 participants. Mean (sd) S-25(OH)D was 84.4 (25.6) nmol/l with 39.6% below 75 nmol/l among 346 controls, and 110.9 (35.7) nmol/l and 15.0% among 1223 PTB patients. Time of recruitment, religion, marital status, occupation, PTB and HIV, and elevated S-AGP were predictors of S-25(OH)D, while age, sex, smoking and alcohol intake were not. S-25(OH)D was highest in 2006 compared to subsequent years, and in the first compared to subsequent quarters. PTB patients had 15.4 (95% CI 11.2, 19.7) nmol/l higher S-25(OH)D than controls, and HIV+ had 9.1 (95% CI 5.5, 12.7) nmol/l higher levels than HIV patients. As seen in the Table, elevated S-AGP was a positive predictor of S-25(OH)D, and explained most of the difference by PTB, but not HIV, status.

In conclusion, hypovitaminosis D was common in Tanzania, with considerable secular and seasonal variation. In contrast to previous studies⁽²⁾, PTB and HIV and elevated acute phase response were associated with higher S-25(OH)D. This could be because infections increasing S-25(OH)D, either due increased vitamin D status or to an effect on the validity of S-25(OH)D as a marker of vitamin D status during the acute phase response.