What are the reasons for VDD in TB patients?
There is paucity of data that explain the reasons for VDD in patients with TB. TB causes weight loss and micronutrient deficiencies by increasing nutritional requirements, changing metabolic processes, or decreasing appetite and causing a reduction in food intake [36]. Vitamin D is required for immune modulation and infection with Mycobacterium tuberculosis binds to toll-like receptors (TLR 2/1) on macrophages, leading to upregulation of 1-a-hydroxylase gene expression to promote greater conversion of 25-OH-D to 1,25-(OH)2-D. This phenom- enon accounts for the drop in 25-OH-D, an indicator for VDD [24].
TB may lead to changes in dietary vitamin D intake and sun exposure through a reduction in appetite and by restricting outdoor physical activities. Patients with TB who have very little adipose tissue are unable to store vitamin D, so they have no reserves when external sources are lacking [20]. TB and its treatment also may have direct biological effects on the