The Dietary Reference Intakes are a set of nutrient guidelines for healthy people. These guidelines include the Recommended Dietary Allowance (RDA). This is the average daily level of nutrients that nearly all healthy people should take to meet their nutrient needs. They also include the Tolerable Upper Intake Level (UL). This is the highest amount of a nutrient a healthy person could take before it could cause a health problem.

A third guideline is Adequate Intake (AI). This is used only when there isn't enough information about a nutrient to set the RDA. It's the level that experts assume will provide enough of that nutrient.

These guidelines are issued by the Food and Nutrition Board of the National Academy of Sciences. This is an independent nonprofit science group. The guidelines are updated from time to time based on the latest data.