Carotenoids

Also indexed as: Carotenes

What are they?

Carotenoids are a highly colored (red, orange, and yellow) group of fat-soluble plant pigments. All organisms, whether bacteria or plants, that rely on the sun for energy contain carotenoids. Their antioxidant effects enable these compounds to play a crucial role in protecting organisms against damage during photosynthesis—the process of converting sunlight into chemical energy.

In humans, carotenoids play two primary roles: All exert antioxidant activity, but some are also converted into vitamin A. Of the 600 carotenoids that have been identified, about 30 to 50 are believed to have vitamin A activity. Carotenoids the body converts to vitamin A are referred to as "provitamin A" carotenoids. The most well known of this group are beta-carotene and alpha-carotene. Some of the better known carotenoids without provitamin A activity—but with very high antioxidant activity—are lutein, lycopene, and zeaxanthin.¹ ²

Preliminary and experimental studies suggest that a higher dietary intake of carotenoids offers protection against developing certain cancers (e.g., lung, skin, uterine, cervix, gastrointestinal tract), macular degeneration, cataracts, and other health conditions linked to oxidative or free radical damage.³ ⁴ ⁵ ⁶ However, two double-blind studies have shown that supplementation with isolated synthetic beta-carotene does not reduce the risk of lung cancer and may even increase that risk in smokers.⁷ ⁸ This finding suggests that foods that are high in carotenoids may protect against cancer in humans for reasons unrelated to their carotenoid content, that synthetic beta-carotene may have different effects from natural beta-carotene (which is somewhat structurally distinct), or that carotenoids may need to be taken together or with supportive antioxidants (e.g., vitamin C, vitamin E, selenium) in order to reduce the risk of cancer. Researchers have yet to determine which of these possibilities is true.

A high intake of carotenoids from dietary sources has been shown to be protective against heart disease in several population-based studies.⁹ ¹⁰ However, a high level of these antioxidants might simply be a marker for diets high in fruits and vegetables known to contain protective substances other than carotenoids. Furthermore, a diet rich in carotenoids tends to be lower in saturated fat and cholesterol and higher in fibre, which has also found to be protective against heart disease.

Because of their antioxidant activity, it has been suggested that beta-carotene and other carotenoids might protect against atherosclerosis by preventing oxidative damage to serum cholesterol. However, research is conflicting in this area. One thing is clear—carotenoids are significantly less effective in protecting against damage to serum cholesterol than is vitamin E. While feeding people beta-carotene has been shown to prevent oxidative damage to cholesterol in some trials,¹¹ other studies have reported that beta-carotene does not protect cholesterol from oxidative damage.¹² ¹³

Just as in the case of cancer prevention, while a high intake of carotenoid-rich foods appears to be protective against cardiovascular disease, the same is not true for supplementation with synthetic beta-carotene. Double-blind intervention trials wherein people are supplemented with beta-carotene alone or placebo have not found benefit for synthetic beta-carotene supplementation. In fact, three of four trials have reported a higher risk of cardiovascular disease in the beta-carotene groups compared with those receiving placebo.¹⁴ ¹⁵ ¹⁶ ¹⁷ While these outcomes prove that synthetic beta-carotene does not protect against heart disease, the effects of natural beta-carotene and other carotenoids have yet to be tested in intervention trials assessing effects on heart disease.

A potential problem with much of the research on carotenoids in cardiovascular disease has been the focus on beta-carotene. A preliminary study found a strong association between dietary sources of lycopene, not beta-carotene, and reduced risk of heart attacks.¹⁸ Lycopene exerts greater antioxidant activity compared to beta-carotene, and lycopene has also been reported to protect cholesterol against oxidative damage.¹⁹

Where are they found?

Carotenoids are found in all plant foods. In general, the greater the intensity of colour, the higher the level of carotenoids. In green leafy vegetables, beta-carotene is the predominant carotenoid. In the orange colored fruits and vegetables—such as carrots, apricots, mangoes, yams, winter squash—beta-carotene concentrations are high, but other pro-vitamin A carotenoids typically predominate. Yellow vegetables have higher concentrations of yellow carotenoids (xanthophylls), hence a lowered pro-vitamin A activity; but some of these compounds, such as lutein, may have significant health benefits, potentially due to their antioxidant effects. The red and purple vegetables and fruits—such as tomatoes, red cabbage, berries, and plums—contain a large portion of non-vitamin A–active carotenoids. Pulses, grains, and seeds are also significant sources of carotenoids. Carotenoids are also found in various animal foods, such as salmon, egg yolks, shellfish, milk, and poultry. A variety of carotenoids is also found in carrot juice and “green drinks” made from vegetables, dehydrated barley greens, or wheat grass.

Synthetic beta-carotene is available as a supplement. Mixed carotenoids (including the natural form of beta-carotene) are also available in supplements derived from palm oil, algae, and carrot oil.

Carotenoids have been used in connection with the following conditions (refer to the individual health concern for complete information):

Science Ratings

Health Concerns

Cataracts (prevention)

Heart disease (prevention)

Macular degeneration (prevention) (lutein, zeaxanthin, lycopene)

Sickle cell anaemia

Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars

Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star

For a herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Who is likely to be deficient?

Carotenoid deficiency is not considered a classic nutritional deficiency like scurvy or beri-beri (severe vitamin C and vitamin B1 deficiencies, respectively). However, given the possible health benefits of carotenoids, most doctors recommend adequate intake. People who do not frequently consume carotenoid-rich foods or take carotenoid supplements are likely to be taking in less than adequate amounts, though optimal levels remain unknown. Also, deficiency may be found in people with chronic diarrhoea or other disorders associated with impaired absorption.

How much is usually taken?

Whether people who already consume a diet high in fruits and vegetables would benefit further from supplementation with a mixture of carotenoids remains unknown. While smokers clearly should not supplement with isolated synthetic beta-carotene, the effect in smokers of taking either natural beta-carotene or mixed carotenoids is not clear.

Nonetheless, based on health-promoting effects associated with these levels in preliminary research, some doctors recommend that most people supplement with up to 25,000 IU (15 mg) per day of natural beta-carotene and approximately 6 mg each of alpha-carotene, lutein, and lycopene.

Are there any side effects or interactions?

Carotenoids are generally regarded as safe, based primarily on studies with beta-carotene. Increased consumption of carotenoids may cause to the skin to turn orange or yellow—a condition known as “carotenodermia.” This occurrence is completely benign and is unrelated to jaundice—the yellowing of the skin that can result from liver disease or other causes.

Until more is known, people especially smokers should not supplement with synthetic beta-carotene. Two double-blind studies have shown that supplementation with isolated synthetic beta-carotene may increase the risk of lung cancer in people who smoke.²⁰ ²¹ Moreover, three of four studies have found small increases in the risk of heart disease in people assigned to take synthetic beta-carotene compared with those assigned to take placebo.²² ²³ ²⁴ ²⁵

Are there any drug interactions?
Certain medicines may interact with carotenoids. Refer to drug interactions for a list of those medicines.

References
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1. Krinsky NI. The antioxidant and biological properties of the carotenoids. Ann NY Acad Sci 1998;854:443-7 [review].

2. Russell RM. Physiological and clinical significance of carotenoids. Int J Vitam Nutr Res 1998;68:349-53 [review].

3. Cooper DA, Eldridge AL, Peters JC. Dietary carotenoids and lung cancer: a review of recent research. Nutr Rev 1999;57:133-45 [review].

4. Gerster H. Anticarcinogenic effect of common carotenoids. Int J Vitam Nutr Res 1993;63:93-121.

5. Rock CL. Carotenoids: biology and treatment. Pharmacol Ther 1997;75:185-97 [review].

6. Landrum JT, Bone RA, Kilburn MD. The macular pigment: a possible role in protection from age-related macular degeneration. Adv Pharmacol 1997;38:537-56.

7. Albanes D, Heinone OP, Taylor PR, et al. Alpha-tocopherol and beta-carotene supplements and lung cancer incidence in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study: effects of base-line characteristics and study compliance. J Natl Cancer Inst 1996;88:1560-70.

8. Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med 1996;334:1150-5.

9. Kritchevsky SB. Beta-carotene, carotenoids and the prevention of coronary heart disease. J Nutr 1999;129:5-8 [review].

10. Palace VP, Khaper N, Qin Q, Singal PK. Antioxidant potentials of vitamin A and carotenoids and their relevance to heart disease. Free Radic Biol Med 1999;26:746-61.

11. Levy Y, Ben-Amotz A, Aviram M. Effect of dietary supplementation of different beta-carotene isomers on lipoprotein oxidative modification. J Nutr Environ Med 1995;5:13-22.

12. Reaven PD, Ferguson E, Naveab M, Powell FL. Susceptibility of human LDL to oxidative modification. Effects of variations in beta-carotene concentration and oxygen tension. Arterioscler Thromb 1994;14:1162-9.

13. Reaven PD, Khouw A, Beltz WF, et al. Effect of dietary antioxidant combinations in humans. Protection of LDL by vitamin E but not by beta-carotene. Arterioscler Thromb 1993;13:590-600.

14. Greenburg ER, Baron JA, Karagas MR, et al. Mortality associated with low plasma concentration of beta carotene and the effect of oral supplementation. JAMA 1996;275:699-703.

15. Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med 1996;334:1150-5.

16. 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. N Engl J Med 1994;330:1029-35.

17. 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. N Engl J Med 1996;334:1145-9.

18. Kohlmeier L, Kark JD, Gomez-Gracia E, et al. Lycopene and myocardial infarction risk in the EURAMIC Study. Am J Epidemiol 1997;146:618-26.

19. Argarwal S, Rao AV. Tomato lycopene and low density lipoprotein oxidation: a human dietary intervention study. Lipids 1998;33:981-4.

20. Albanes D, Heinone OP, Taylor PR, et al. Alpha-tocopherol and beta-carotene supplements and lung cancer incidence in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study: effects of base-line characteristics and study compliance. J Natl Cancer Inst 1996;88:1560–70.

21. Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med 1996;334:1150–5.

22. Greenburg ER, Baron JA, Karagas MR, et al. Mortality associated with low plasma concentration of beta carotene and the effect of oral supplementation. JAMA 1996;275:699–703.

23. Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med 1996;334:1150–5.

24. 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. N Engl J Med 1994;330:1029–35.

25. 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. N Engl J Med 1996;334:1145–9.

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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or chemist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires March 2007.

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