International Unit
Quantity of a nutrient producing a particular biologic effect; varies by nutrient.
Also: IU
Standardized biological-activity unit used historically for fat-soluble vitamins (A, D, E). Conversion factors translate IU into mass units (e.g., µg retinol activity equivalents).
How one textbook covers it
Advanced Nutrition and Human Metabolism, 8th ed. (Gropper) — Glossary
Standardized biological-activity unit used historically for fat-soluble vitamins (A, D, E). Conversion factors translate IU into mass units (e.g., µg retinol activity equivalents).