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Vitamin D and tuberculosis: review and association in three rural provinces of Afghanistan.

OBJECTIVES
1) To update the 2006 systematic review and meta-analysis by Nnoaham & Clarke exploring the association between serum vitamin D and risk of active tuberculosis (TB) following discrepant evidence; and 2) to identify whether TB and vitamin D are associated in rural Afghanistan.


METHODS
Systematic review and meta-analysis of studies published between January 1980 and June 2014 using Nnoaham & Clarke's methodology. For this case-control study, 90 age- and sex-matched pairs were recruited from rural provinces, and blood 25-hydroxyvitamin D concentrations were measured using enzyme-linked immunosorbent assay.


RESULTS
Sixteen studies were eligible for review. Eleven showed differences between vitamin D levels in TB patients and controls, two showed partial differences and three showed none. Studies on African and European populations show lower vitamin D levels in TB patients, but results from Asia vary. No significant differences were found in vitamin D levels in our rural Afghan population. Controls had a higher body mass index (BMI) (mean control BMI 21.50 kg/m(2), mean case BMI 18.86 kg/m(2), P < 0.001), and were more likely to have been employed (40% of controls, 15.6% of cases, P = 0.002).


CONCLUSION
Genetic differences may account for the differences among study results in the systematic review. Vitamin D levels are not associated with TB among Afghans living in these rural provinces.