Carotenoids are naturally occurring organic pigments that are produced in chloroplasts and chromoplasts through a photosynthetic process in plants (some bacteria and fungi can also produce them). Most animals, however, cannot manufacture carotenoids, so they must be obtained in the diet.
The carotenoid family consists of over six hundred known members. They are split into two sub-families: the carotenes (pure hydrocarbons) and xanthophylls (which contain oxygen). In plants, carotenoids serve two primary roles: light absorption (for use in photosynthesis) and photo-oxidative protection.
All carotenoids act like antioxidants. Three carotenoids, including alpha-carotene, beta-carotene, and beta-cryptoxanthin possess vitamin A activity, when they are cleaved through the action of the enzyme beta-carotene 15,15′-monooxygenase into active retinol (vitamin A). In the eye, lutein, astaxanthin, and zeaxanthin work to absorb damaging ultraviolet rays and are protective to the macula and retina.
Many research studies have tracked the consumption of carotenoids and their relationship to disease. Carotenoid-rich diets from fruits and vegetables almost uniformly reduce overall mortality and lower risk of chronic diseases including certain cancers, cardiovascular disease, and eye health.
There is no known deficiency signs for insufficient carotenoid intake (apart from concurrent vitamin A deficiency). Given the well-researched benefits of carotenoids, it is wise to consider a diet high in carotenoid-rich foods, or to supplement.
The bioavailability of carotenoids varies with type and other factor. Beta-carotene has been shown to be around 14 percent absorbed when compared to 67 percent when a meal of mixed vegetables is consumed.  Studies have shown that adding fat to the diet along with carotenes increases absorption of many types of carotenoids (alpha-carotene, beta-carotene, lycopene, and lutein).,
No RDA exists for carotenoids, but some health practitioners suggest 25,000 iu per day.
Refer to individual carotenoids for a review of their research:
 Unlu NZ, Bohn T, Clinton SK, Schwartz SJ. Carotenoid absorption from salad and salsa by humans is enhanced by the addition of avocado or avocado oil. J Nutr. 2005 Mar;135(3):431-6. PMID: 15735074.
 Kopec RE, Cooperstone JL, Schweiggert RM. Avocado consumption enhances human postprandial provitamin A absorption and conversion from a novel high-β-carotene tomato sauce and from carrots. J Nutr. 2014 Aug;144(8):1158-66. PMID: 24899156.