Dysvitaminosis is a disease caused by either a deficiency or excess of a particular vitamin — the umbrella term for vitamin imbalance in either direction. Deficiency produces the classic deficiency diseases: scurvy without vitamin C, rickets without vitamin D, beriberi without thiamine. Excess produces the toxicities: vitamin A damaging the liver and raising intracranial pressure, vitamin D driving blood calcium dangerously high, vitamin B6 injuring peripheral nerves at megadoses. The concept captures an essential truth of nutrition — that vitamins are beneficial within a range and harmful outside it, and that more is not better. Both ends of the spectrum are seen in practice: deficiency where diets are poor, excess where supplements are abused. Dysvitaminosis is the word for getting the dose wrong in either direction.