Both high and low serum vitamin D concentrations are associated with tuberculosis: a case-control study in Greenland

Vitamin D deficiency has been associated with increased risk of tuberculosis (TB). Changes from a traditional to a Westernised diet among Greenlanders have resulted in reduced serum vitamin D, leading to considerations of whether preventive vitamin D supplementation should be introduced. The association between vitamin D status and TB was examined to assess the feasibility of vitamin D supplementation in Greenland. This was examined in a case-control study involving seventy-two matched pairs of TB patients (cases) and controls aged 8-74 years. Cases were diagnosed with TB during 2004-6 based on clinical findings in combination with either (1) positive Mycobacterium tuberculosis culture, (2) characteristic X-ray abnormalities together with a positive tuberculin skin test or a positive interferon-gamma release assay or (3) characteristic histology. Controls were individually matched on age (+/- 5 years), sex and district. Serum 25-hydroxyvitamin D (25(OH) D) concentrations were measured and OR of TB were the outcome. Compared with individuals with 25(OH) D concentrations between 75 and 140 nmol/l, individuals with concentrations < 75 nmol/l (OR 6,5; 95% CI 1,8, 23,5) or > 140 nmol/l (OR 6,5; 95% CI 1,9, 22,2) had higher risks of active TB (P 0,003; adjustment for alcohol and ethnicity). Supplementing individuals with low vitamin D to normalise serum 25(OH) D concentrations was estimated to result in a 29% reduction in the number of TB cases. The study indicated that vitamin D supplementation may be beneficial to individuals with insufficient vitamin D concentrations but may increase the risk of TB among individuals with normal or high concentrations.