Tolerable Upper Intake Level

The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects for nearly all individuals in a given life stage group. ULs are established by the National Academies of Sciences and are based on available data about adverse effects. Exceeding the UL increases the risk of toxicity. Key ULs relevant to supplement research include: vitamin A (3,000 mcg RAE), vitamin D (100 mcg/4,000 IU), zinc (40 mg), selenium (400 mcg), and iron (45 mg). Not all nutrients have established ULs — absence of a UL does not mean unlimited safe intake.