what is iu in vitamins

IU stands for International Unit and is a measurement used to quantify the biological effect or potency of vitamins, hormones, enzymes, and other substances. It is particularly used to measure fat-soluble vitamins such as A, D, E, and K. The IU measurement can vary based on the biological activity of the substance per unit of mass or volume, and it provides an international standard for the dosing of these substances. For example, 1 IU of vitamin E is approximately equal to 2⁄3 mg of d-alpha-tocopherol. IU is not used to compare different substances, unlike milligrams (mg) or micrograms (mcg), which measure the mass of one substance to another. While IU was historically used on supplement labels, it has now been phased out in some cases, and you may see micrograms (mcg) instead. Each product has a specific conversion factor, so it is often easiest to rely only on IU for dosing. The IU system was established in the early 1900s to create a standard database of information that consumers and doctors could use to understand the biological effect of specific doses of substances. Therefore, IU is an important measure for understanding the potency of vitamins and other biologically active substances