Success Chemistry

Improve who you are | Become unforgettable


GlossarySuccess Chemistry Staff

Carotenoids are a family of compounds of over 600 fat soluble

plant pigments, which provide much of the color

seen in nature.

For example, carotenoids are responsible

for the red color of tomatoes and the orange color of

carrots. Apart from their aesthetic role, carotenoids are

considered to be beneficial in the prevention of various

diseases, including certain cancers and eye disease. The

beneficial effects of carotenoids are attributed to a small

portion of the hundreds of carotenoids found in nature,

given that only about two dozen are found in human

blood and tissue, and only two in the eye. The carotenoids

that have been most studied in this regard are -carotene,

-carotene, cryptoxanthin, lycopene, lutein, and zeaxanthin.

(See also separate chapters on “-Carotene,”

“Lutein,” and “Lycopene.”) -Carotene and lycopene

belong to a class of carotenoids called carotenes and are

highly fat soluble. Cryptoxanthin, lutein, and zeaxanthin

belong to a class of carotenoids called xanthophylls.

Because xanthophylls contain at least one hydroxyl

group, they are more polar than that of carotenes. Thus, -

carotene, -carotene, and lycopene tend to predominate in

low-density lipoproteins (LDL) in the circulation, whereas

high-density lipoproteins (HDL) are major transporters of

cryptoxanthin, lutein, and zeaxanthin (1). In part, the protection

against chronic disease by carotenoids is thought

to be through their antioxidant activity. Lutein and

zeaxanthin are thought to have an additional protective

role of absorbing damaging blue light that enters the eye.



The most common carotenoids in the U.S. diet are

-carotene, -carotene, -cryptoxanthin, lycopene, lutein,

and zeaxanthin (2). Rich sources of - and -carotene

include carrots and winter squashes. Foods high in

-cryptoxanthin are orange and red fruits and vegetables

such as pumpkin, papayas, and red peppers. Tomatoes account

for approximately 80% of the dietary lycopene (3).

Dark green leafy vegetables such as spinach and kale are

rich sources of lutein and zeaxanthin. The relatively low

bioavailability of carotenoids from foods is, in part, due

to their association with proteins in the plant matrix (4).

Disruption of the plant matrix with chopping, blending,

or cooking can increase carotenoid bioavailability (5).



Carotenoids, being fat soluble, follow the same intestinal

absorption path as dietary fat. Carotenoids are released

from food matrices and solubilized in the gut. This is done

in the presence of fat and conjugated bile acids. As little

as 3 to 5 g of fat in a meal is sufficient for carotenoid absorption

(5,6). Absorption is affected by the same factors

that influence fat absorption. Thus, the absence of bile

or any generalized malfunction of the lipid absorption

system (e.g., small intestinal disease, pancreatic disease)

will interfere with the absorption of carotenoids. Chylomicrons

are responsible for the transport of carotenoid from

the intestinal mucosa to the bloodstream via the lymphatics

for delivery to tissues. Carotenoids are transported in

the plasma exclusively by lipoproteins, being carried predominately

by LDL (carotenes) and HDL (xanthophylls)

(7). The delivery of carotenoids to extrahepatic tissues is

accomplished through the interaction of lipoprotein particles

with receptors and the degradation of lipoprotein


Plant sterols reduce the absorption of cholesterol in

the gut, in part by competing with cholesterol when they

are incorporated into the mixed micelles (8). Stanol and

steryl esters reduce plasma concentrations of carotenoids

(9,10). It is thought that, during the absorption process in

the intestine, plant sterols could displace not only cholesterol

but also these lipophilic molecules and replace them

in incorporation into mixed micelles.



To date, the only known essential function of carotenoids

is as a source of vitamin A. The carotenoids in this category

are -carotene, -carotene, and -cryptoxanthin (11). The

vitaminAactivity of -carotene in food is 1/12 that of vitamin

A (retinol), and vitamin A activity of both -carotene

and -cryptoxanthin is 1/24 that of vitamin A (11).

Most carotenoids have antioxidant activity. -

Carotene and others carotenoids have antioxidant properties

as shown in in vitro and animal models. Mixtures of

carotenoids or associations with others antioxidants (e.g.,

vitamin E) can increase their activity against free radicals

(12). The use of animal models for studying carotenoids is

limited because most of the animals do not absorb or metabolize

carotenoids similarly to humans. Epidemiologic

studies have shown an inverse relationship between

the presence of various cancers and dietary or blood

carotenoid levels (13). However, three out of four intervention

trials using high-dose -carotene supplements did

not show protective effects against cancer or cardiovascular

disease. Rather, the high-risk populations (smokers

and asbestos workers) in these high-dose intervention trials

showed an increase in cancer and angina cases (14–17).


122 Johnson and Russell











Figure 1 Structures of the major dietary carotenoids.

Therefore, carotenoids may promote health when taken at

dietary levels but may have adverse effects when taken

in high dose by subjects who smoke or who have been

exposed to asbestos.

The long chain of alternating double and single

bonds is a characteristic of all carotenoids (Fig. 1). This

feature allows them to absorb light in the visible range

of the light spectrum (18). This may be of particular

importance in the macula of the retina, where lutein

and zeaxanthin are highly concentrated to the exclusion

of all other carotenoids (19). In the macula, lutein

and zeaxanthin absorb blue light to reduce the amount

of light that reaches critical visual structures, thereby

providing some protection from light-induced oxidative

damage (20).



Epidemiologic studies support a protective role of

carotenoids in the prevention of certain major diseases,

including certain cancer and eye disease. The hypothesis

that these antioxidant nutrients may protect against

certain diseases is plausible, given the putative role of

oxidative damage in the etiology or these diseases. However,

clinical trials have suggested that supplementation

with high dose of -carotene may have an adverse effect

on the incidence of cancer in smokers and workers

exposed to asbestos. Current recommendations include

diets high in fruits and vegetables, which are rich sources

of carotenoids.



1. Wang W, Connor SL, Johnson EJ, et al. The effect of a high

lutein and zeaxanthin diet on the concentration and distribution

of carotenoids in lipoproteins of elderly people with

and without age-related macular degeneration. Am J Clin

Nutr 2007; 85:762–769.

2. USDA. USDA-NCC Carotenoid Database for U.S. Foods—

1998, 1998.

3. Clinton SK. Lycopene: Chemistry, biology, and implications

for human health and disease. Nutr Rev 1998; 56:35–51.

4. Yeum KJ, Russell RM. Carotenoid bioavailability and bioconversion.

Annu Rev Nutr 2002; 22:483–504.

5. van Het Hof KH,West CE,Weststrate JA, et al. Dietary factors

that affect the bioavailability of carotenoids. J Nutr 2000;


6. Jalal F, Nesheim MC, Agus Z, et al. Serum retinol concentrations

in children are affected by food sources of beta-carotene,

fat intake, and anthelmintic drug treatment. Am J Clin Nutr

1998; 68:623–629.

7. Clevidence BA, Bieri JG. Association of carotenoids with human

plasma lipoproteins. In: Abelson JN, Simon MI, eds.

Methods in Enzymology. San Diego, CA: Academic Press,

Inc., 1993:33–46.

8. Ostlund RE. Phytosterols in human nutrition. Annu Rev

Nutr 2002; 22:533–549.

9. Hallikainen MA, Sarkkinen ES, Gylling H, et al. Comparison

of the effects of plant sterol ester and plant stanol ester enriched

margarines in lowering serum cholesterol concentrations

in hypercholesterolaemic subjects on a low-fat diet.

Eur J Clin Nutr 2000; 54:715–725.

10. Richelle M, Enslen M, Hager C, et al. Both free and esterified

plant sterols reduce cholesterol absorption and

the bioavailability of -carotene and -tocopherol in

Carotenoids Overview 123

normocholesterolemic humans.AmJ Clin Nutr 2004; 80:171–


11. Institute of Medicine, Food, and, Nutrition, Board. Dietary

reference intakes of vitamin C, vitamin D, selenium, and

carotenoids. Washington, D.C.: National Academy Press,


12. Bohm F, Edge R, McGarvey DJ, et al. Beta-carotene with

vitamins E and C offers synergistic cell protection against

NOx. FEBS Lett 1998; 436:387–389.

13. Block G, Patterson B, Subar A. Fruit, vegetables and cancer

prevention: A review of the epidemiological evidence. Nutr

Cancer 1992; 18:1–29.

14. The Alpha-Tocopherol Beta-Carotene Cancer Prevention

Study Group. The effect of vitamin E and beta-carotene

on the incidence of lung cancer and other cancers

in male smokers. New Engl J Med 1994; 330:1029–


15. Hennekens CH, Buring JE, Manson JE, et al. Lack of effect

of long-term supplementation with beta-carotene on the incidence

of malignant neoplasms and cardiovascular disease.

New Engl J Med 1996; 334:1483–1491.

16. Blot WJ, Li JY, Taylor PR, et al. Nutrition intervention trials

in Linxian, China: Supplementation with specific vitamin/

mineral combinations, cancer incidence, and disease-specific

mortality in the general population. J Natl Cancer Inst 1993;


17. Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a

combination of beta-carotene and vitamin A on lung cancer

and cardiovascular disease. New Engl J Med 1996; 334:1150–


18. Halliwell B, Gutteridge JMC. Free Radicals in Biology and

Medicine, 3rd ed. New York: Oxford University Press, 1999.

19. Bone RA, Landrum JT, Tarsis SE. Preliminary identification

of the human macular pigment. Vision Res 1985; 25:1531–


20. Krinsky NI, Landrum JT, Bone RA. Biologic mechanism of

the protective role of lutein and zeaxanthin in the eye.