Tuberculosis and vitamin D: what's the rest of the story?

Both protein–energy undernutrition and specific micronutrient deficiencies debilitate the cell-mediated immune system important in protection against tuberculosis.¹ However, once tuberculosis develops, the disease itself induces a catabolic state resulting in negative nitrogen balance and micronutrient deficiencies. Generations of clinicians treating patients with tuberculosis believed that nutritional support was crucial to proper patient care. Why, then, has it been so difficult to prove through randomised controlled clinical trials that nutritional interventions improve tuberculosis treatment outcomes? Findings from systematic reviews^{2, 3, 4, 5, 6} have not shown any clear, consistent benefit in terms of tuberculosis-specific outcomes, although they do show improvements in nutritional status.