Carotenoids refer to over 500 substances which naturally occur in fruits and vegetables. Some 50 carotenoids act as precursors to vitamin A, with beta-carotene being the most well-known and most prevalent. More recently, lycopene has become another popular carotenoid due to its various healing properties. the best food sources of carotenoids are yellow and dark green vegetables, orange fruits, tomatoes, watermelons, and cherries

Carotenoids primarily act as antioxidants in the body, and are also capable of minimizing the formation of abnormal and precancerous cells and preventing age-related vision problems. Some researchers also speculate that carotenoids can improve immune function by stimulating immune antibodies, lymphocytes, and natural killer and T-helper cells. Symptoms of carotenoid deficiency include diminished immune function, free radical damage, and increased susceptibility to various cancers and cardiovascular illness.