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.