Recommended Dietary Allowance (RDA) - the average daily dietary nutrient intake level sufficient to meet the nutrient requirement of nearly all - ~97% - healthy individuals in a particular life stage and gender group.
The process for setting the RDA depends on being able to set an Estimated Average Requirement (EAR). If an EAR cannot be set, no RDA will be set. The EAR is the daily intake value of a nutrient that is estimated to meet the nutrient requirement of half the healthy individuals in a life stage and gender group.
The RDA is set at the EAR plus twice the standard deviation (SD) if known (RDA = EAR + 2 SD). If data about variability in requirements are insufficient to calculate a standard deviation, a coefficient of variation for the EAR of 10% is ordinarily assumed (RDA = 1.2 x EAR).
The RDA for a nutrient is a value to be used as a goal for dietary intake by healthy individuals. The RDA is not intended to be used to assess the diets of either individuals or groups or to plan diets for groups.
Carotenoids are a class of more than 750 pigments synthesized by plants, algae, and photosynthetic bacteria. These richly colored molecules are the sources of the yellow, orange, and red colors of many plants. Fruit and vegetables provide most of the 40 to 50 carotenoid phytonutrients found in the human diet.
The most common carotenoids in North American diets are α-carotene, β-carotene, β-cryptoxanthin, lutein, zeaxanthin, and lycopene.
Provitamin A carotenoids - α-carotene, β-carotene, and β-cryptoxanthin - can be converted by the body to retinol (vitamin A), but not lutein, zeaxanthin, and lycopene.
Dietary lutein and zeaxanthin help maintain optimal visual function - they absorb damaging blue light that enters the eye.
The results of observational studies suggest that diets high in carotenoid-rich fruit and vegetables are associated with reduced risks of cardiovascular disease and some cancers. But high-dose β-carotene supplements did not.