Water-soluble vitamins (B-complex + C): Not stored in body → daily dietary intake essential. Excess excreted in urine. Act primarily as coenzymes (B vitamins) or antioxidants (vitamin C).

Key B vitamins for JEE: B1 (thiamine, beriberi), B2 (riboflavin, cheilosis), B3/niacin (pellagra — 3 D's: dermatitis, diarrhea, dementia), B6 (pyridoxine), B12 (cobalamin, pernicious anemia — only vitamin containing a metal: cobalt), Folic acid (megaloblastic anemia, neural tube defects).

Vitamin C (ascorbic acid): Scurvy (bleeding gums, poor wound healing). Strong reducing agent. Destroyed by cooking.

Fat-soluble vitamins (A, D, E, K — "ADEK"): Stored in liver and adipose tissue. Can accumulate to toxic levels (hypervitaminosis). A: retinol, night blindness/xerophthalmia. D: calciferol, rickets/osteomalacia (synthesized in skin from cholesterol + UV light). E: tocopherol, antioxidant, infertility. K: phylloquinone, blood clotting (required for prothrombin synthesis).