A supplement is a product intended to supplement the diet, not to be use as a food or as a sole item of a meal or the diet. Nutritional supplementation may include vitamins, minerals, essential nutrients, accessory nutrients or neutraceuticals.

Recommended Dietary Allowance (RDA)
RDAs have been set since 1940s by various Food and Nutrition Boards; they were originally intended to reduce severe states of nutritional deficiency e.g. scurvy, rickets and beriberi. RDAs were designed to assess diets in groups of people not individuals, because individual RDAs vary depending on diet and lifestyle. “Individuals with special nutritional needs are not covered by the RDAs.” (National Research Council, Recommended Dietary Allowances, National Academy Press, DC, 1989)

Recommended Daily Intake (RDI)
RDI are “the levels of intake of essential nutrients considered, on the basis of available scientific knowledge, to be adequate to meet the needs of practically all healthy people.” (Braun & Cohen 2005). Based on preventing nutrient deficiency signs in healthy people, they do not take individual requirements into account. E.g. tannin/phytates and iron. Often known to change when new evidence emerges and can vary from country to country, so not a definitive guide. They have limited clinical use. RDAs and RDIs do not reduce the risk of developmental or degenerative diseases such as CVD or neural tube defects.

Daily Value (DV)
Food product labeling. Two sets of references: Daily Reference Values (DRV) and RDI. DRVs are a set of dietary references that apply to fat, saturated fat, cholesterol, carbohydrate, protein, fibre, sodium and potassium.

Optimum Daily Intake (ODI)
The amount of nutrients needed for vibrant health (Balch & Balch). Higher amounts than RDA. This is generally where nutritionists/naturopaths prescribe. Scientific research shows the optimal level for nutrients are much higher than RDAs. RDAs do not take into account lifestyle factors, such as smoking, where is has been ascertained (by the Food and Nutrition Board), that they require at least twice as much vit C as nonsmokers.