GC and vitamin D deficiency: Variability in the results of different studies could be due to the lack of a standard definition of vitamin D deficiency, the type of vitamin D measured (calcidiol/calcitriol), and different types and doses of vitamin D administered to study participants, polymorphisms of the genes that code for vitamin D receptors and vitamin D binding protein, interaction of vitamin D with anti-tubercular drugs, other vitamins and micronutrients deficiencies, and environmental and social factors.