Clinical meaning
Vitamins are organic micronutrients essential for enzymatic reactions, cellular metabolism, and tissue maintenance. Fat-soluble vitamins (A, D, E, K) are stored in adipose tissue and the liver, while water-soluble vitamins (B complex, C) require regular dietary intake. Vitamin A deficiency impairs rhodopsin synthesis causing night blindness and weakens epithelial barriers. Vitamin D deficiency disrupts calcium-phosphorus homeostasis leading to rickets in children and osteomalacia in adults. Vitamin B12 deficiency causes megaloblastic anemia and peripheral neuropathy due to impaired DNA synthesis and myelin maintenance. Vitamin C deficiency (scurvy) weakens collagen synthesis causing bleeding gums, petechiae, and poor wound healing. Thiamine (B1) deficiency causes beriberi and Wernicke encephalopathy through impaired glucose metabolism in neural tissue.
Exam relevance
Risk factors: - Chronic alcoholism depleting thiamine and folate stores - Strict vegan diet without B12 supplementation - Malabsorptive conditions (celiac disease, Crohn's, gastric bypass) - Elderly patients with poor dietary intake and isolation - Prolonged parenteral nutrition without vitamin supplementation