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Carotenoids are a class of approximately 600 naturally occurring, fat-soluble pigment compounds commonly found in fruits, vegetables, and microorganisms that have prominent health-promoting properties. Carotenoids give cantaloupes, carrots, sweet potatoes, tomatoes, and other fruits and vegetables their yellow, orange, red, and purple color. Although the most common carotenoid in higher plants is beta carotene, various others also occur naturally and may have beneficial health effects that rival beta carotene’s. Alpha carotene, after beta the most common carotene, is less potent than beta as a vitamin A precursor but, according to animal studies, more potent as a cancer controller. Lutein, which is abundant in yellow/orange vegetables and fruits, and lycopene, found mostly in tomatoes, have potent antioxidant capabilities. Other beneficial carotenoids include gamma carotene, beta-cryptoxanthin, zeaxanthin, and xanthophylls.

Why is it essential? Beta carotene plays a major role as a vitamin A precursor, as do about 10 percent of other carotenoids. Beta carotene and other related carotenoids are increasingly being recognized as having further important health-related roles in the body. Many carotenoids that are not vitamin A precursors, including lutein and lycopene, are powerful antioxidants. Carotenoids also help regulate cell growth, boost immune response, and protect the skin from UV damage. Lycopene and others may also help to reduce the risk of cancer and heart disease.

Benefits and uses: Carotenoids have numerous preventive and therapeutic effects. Lutein protects the retina of the eye from sunlight and may help prevent age-related macular degeneration, the leading cause of blindness in older adults. Increased intakes of lycopene and tomato-based foods may be associated with reduced cancer risk. Studies have linked high blood levels of carotenoids with fewer heart attacks and deaths than those with lowest levels of carotenoids. Researchers have shown that lycopene, the most abundant carotenoid in the prostate, can protect against prostate cancer. Lycopene also reduces the risk for cancers of the gastrointestinal tract and for precancerous changes of the cervix.

Daily requirement: There is no RDA for carotenoids per se, although it is possible to meet the vitamin A RDA by taking sufficient amounts of beta carotene or other percursors. The RDA for vitamin A for adults is 800 to 1,000 Retinol Equivalents. This can be met by taking approximately 5 to 6 mg of beta carotene, or twice as much of the less potent precursors alpha carotene, gamma carotene, beta carotene, or cryptoxanthin.

Deficiency risk factors: A deficiency in other nutrients, particularly zinc and vitamin C, may reduce carotenoid absorption and utilization.

Optimal intake: An optimal daily dose for an average adult is 25,000 to 50,000 IU (15 to 30 mg) of beta carotene plus mixed carotenoids. It is possible that carotenoids enhance each other’s absorption and act much more effectively together than individually. Carotenoid supplements should be taken with food to improve absorption.

Food sources: Dark green leafy vegetables and orange-yellow fruits and vegetables are good sources of beta and alpha carotenes. Concentrated green foods, such as spirulina and blue-green algae, and the dried juice of young shoots of cereal plants such as barley and wheat grass, are rich in beta carotene as well as other carotenoids. Spinach, kale, collard greens, corn, carrots, and peas are good sources of Lutein. Tomatoes and green peppers are high in lycopene. Eating a diverse, carotenoid-rich diet supplies an estimated 5 to 10 mg of beta carotene daily; average adult consumption of beta carotene on the standard American diet is much lower at 1to 2 mg daily.

Recent findings: The dietary intake of several carotenoids in 332 lung cancer patients was compared to that of 865 cancer-free controls. After adjusting for smoking and other risk factors, researchers reported that the lowest risk of lung cancer occurred in those with the highest intake of beta carotene, alpha carotene, and lutein.¹ This study also reported that those who ate more than ten servings per week of tomato-based foods had a 35 percent decreased risk of prostate cancer compared to those eating less than 1.5 weekly servings. Researchers have begun to demonstrate beneficial health effects in some of the lesser-known carotenoids. A Japanese researcher recently confirmed anti-carcinogenic properties in fucoxanthin, peridinin, and phytoene.² Other studies have recently confirmed beneficial antioxidant effects³; shown that carotenoids act through channels distinct from either their role as vitamin A precursors or as antioxidants⁴; and further supported carotenoids’ preventive role in heart disease.⁵

Safety: There are no reports of adverse effects even from eating high amounts of carotenoids. Eating too much beta carotene, such as more than 100,000 IU per day for weeks or months, can give the skin a slightly orange hue until intake is reduced.

Types of products: Beta carotene comes in capsules, tablets, softgels, and powders. Potency typically ranges from 10,000 to 50,000 IU, with the most popular potency probably being 25,000 IU. A few products provide as much as 83,000 IU per capsule. Some supplements contain only beta carotene (derived either synthetically or from carrots or algae), while others have added various carotenoids and/or preformed vitamin A. Mixed-carotene and multi-carotenoid supplements are becoming increasingly popular.

References

1. Le Marchand, L., et al., "Intake of specific carotenoids and lung cancer risk," Cancer Epidemiology (1993), 2:183–87
2. Nishino, H., "Cancer prevention by carotenoids," Mutat Res (1998), 402(1–2):159–63
3. Dixon, Z.R., et al., "The effect of a low carotenoid diet on malondialdehyde-thiobarbituric acid (MDA-TBA) concentrations in women: a placebo-controlled double-blind study," J Am Coll Nutr (1998), 17(1):54–58
4. Rauscher, R., et al. "In vitro antimutagenic and in vivo anticlastogenic effects of carotenoids and solvent extracts from fruits and vegetables rich in carotenoids," Mutat Res (1998), 413(2):129–42
5. Kritchevsky, S.B., et al., "Provitamin A carotenoid intake and carotoid artery plaques: the Atherosclerosis Risk in Communities Study," Am J Clin Nut (1998), 68(3):726–33.

Supporting References

1. Seddon JM, Ajani UA, Sperduto RD, et al. Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. JAMA 1994;272:1413-20.
2. Giovannucci E, Ascherio A, Rimm EB, et al. Intake of carotenoids and retinol in relation to risk of prostate cancer. JNCI 1995;87:1767-76.
3. Mills PK, Beeson WL, Phillips RL, Fraser GE. Cohort study of diet, lifestyle, and prostate cancer in Adventist men. Cancer 1989;64:598-604.
4. Carter HB, Coffey DS. The prostate: an increasing medical problem. Prostate 1990;16:39-48.
5. Hsing AW, Comstock GW, Abbey H, Polk F. Serologic precursors of cancer. Retinol, carotenoids, and tocopherol and risk of prostate cancer. JNCI 1990;82:941-6.
6. Levy J, Bosin E, Feldman B, Giat Y, et al. Lycopene is a more potent inhibitory of human cancer cell proliferation than either beta-carotene or beta-carotene. Nutr Cancer 1995;24:257-66.
7. Franceshci S, Bidoli E, La Vecchia C, et al. Tomatoes and risk of digestive-tract cancers. Int J Cancer 1994;59:181-4.
8. Van Eenwyk J, Davis FG, Bowne PE. Dietary and serum carotenoids and cervical intraepithelial neoplasia. Int J Cancer 1991;48:34-8.
9. Wahlqvist Ml, et al. Changes in serum carotenoids in subjects with colorectal adenomas after 24 months of beta-carotene supplementation. Australian Polyp Prevention Investigators. Am J Clin Nutr 1994;60:936-943

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