Vitamin Deficiency Syndromes

Vitamin deficiency is a mechanism, not a single presentation. The bedside clue is the tissue that is losing function. Vitamin D deficiency develops when cutaneous synthesis, dietary supply, or gastrointestinal absorption is inadequate. Less vitamin D means less effective calcium absorption from the intestine. In adults, the resulting mineralization problem produces osteomalacia; in children, it produces rickets. Bone pain, proximal muscle weakness, and fragility fractures fit the adult pattern, while impaired skeletal growth or bone deformity raises concern in a child. Vitamin B12 deficiency affects two systems at once. Impaired DNA synthesis produces megaloblastic anaemia, while impaired myelin maintenance can produce paresthesias, reduced proprioception, gait disturbance, and other neurologic changes. The neurologic component changes the urgency: untreated injury may become irreversible even when the anaemia is not dramatic. Fatigue alone does not distinguish these syndromes. Fatigue with numbness, loss of balance, or a strict vegan diet points toward B12 assessment; bone pain or proximal weakness in a person with malabsorption points toward vitamin D assessment.