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Carotenoids are a large group of pigments which provide the red, yellow and orange colours in plants. Most importantly in food, fruits and vegetables such as tomatoes, apricots, peppers and carrots. Foods such as these form a large part of the healthy diet of the Mediterranean countries. Scientists studying these foods are aware that the carotenoids provide more than just their colour, as together with vitamins C and E, carotenoids are major Antioxidants. Research indicates that an optimal intake of these important nutrients may help delay or prevent the onset of cancer, heart disease, cataracts and other ageing diseases.
Out of the 500 - 600 carotenoids so far identified, about 40 are found in the human diet of these around 14 are absorbed and used in the body. The most common and those believed to be most significant to human health include Beta Carotene, alpha carotene, cryptoxanthin, zeaxanthin, lycopene and lutein.
Carotenoids are plant pigments that protect plant tissue from becoming burnt and brown in sunlight. Beta Carotene is the main carotenoid, and is the most potent precursor of Vitamin A. Other carotenoids (see below) are also converted to Vitamin A about half as efficiently as Beta Carotene.
The carotenoid to Vitamin A conversion is as follows:
Lutein and Zeaxanthin
As well as acting as vitamin A precursors, carotenoids also act as free radical quenchers. This means they have the capacity to protect delicate cell contents from damage and possibly inactivate mutagens and carcinogens.
Without carotenoids, plants would be destroyed soon after sunrise. Carotenoids provide antioxidant protection from the dangerous Ãƒ¢Ã¢â€š¬Ã‹Å“free radicalÃƒ¢Ã¢â€š¬Ã¢â€¢ molecules which form when the plants are exposed to sunlight. By consuming carotenoid rich foods, we are giving our cells similar antioxidant protection. Carotenoids help defend our cells against damage from free radicals generated by factors like the sun, tobacco smoke, car exhaust fumes, pesticides and of course, the bodyÃƒ¢Ã¢â€š¬Ã¢â€¢s own metabolic processes.
As with B Complex Vitamins and mixed tocopherols in vitamin E, the carotenoids work best when they are together. We know of beta carotene and its antioxidant potential, but now research is investigating the links between nutrition and disease, and the other carotenoids are beginning to attract interest. The most effective all round protection comes from a mix of carotenoids, rather than large intakes of individual ones.
Deficiency symptoms of beta carotene are the same as for vitamin A.
Upper safe level for daily supplementation beta carotene = 20mg
Dietary carotenoids contribute towards total vitamin A intake. There is deemed to be no separate requirement for beta carotene or other carotenoids. However an intake of at least 6 mg per day in total is regarded by many authorities as optimal.
Increasing fresh fruit and vegetable consumption to five portions a day is an ideal way of ensuring an adequate carotenoid intake. This quantity should provide all the Beta Carotene a body needs. A food supplement containing carotenoids will act as an insurance for an individual if their fruit and vegetable consumption is constantly low. The majority of food supplements use dunaliella salina as the source of carotenoids, although some may be derived from palm oil. These two sources contain a combination of the most common carotenoids found in food.
Carotenoids can be taken purely for their vitamin A activity, but the nutrientsÃƒ¢Ã¢â€š¬Ã¢â€¢ free radical quenching capacity also makes them useful in antioxidant supplement (1).
Beta carotene supplementation is recommended before prolonged exposure to hot sun. It can help to protect the Skin from u.v. induced damage and may even protect against skin cancer in the long-term (2).
Beta Carotene has been shown to protect against cardiovascular disease and reduce subsequent coronary events by 50% compared to a placebo (1).
Beta carotene is an extremely safe form of vitamin A, because at very high levels of intake, the bodyÃƒ¢Ã¢â€š¬Ã¢â€¢s beta carotene to vitamin A conversion process slows down dramatically.
The only known side effect occurring with high levels of beta carotene is carotenaemia which is a harmless condition in which the Skin turns a slight orange colour. This is reversible upon stopping beta carotene supplementation. Carotenaemia may occur at dosages of approximately 30mg daily and above.
Those who work with or have been exposed to asbestos are advised to avoid beta carotene supplements (3,4).
Airway and circulating levels of carotenoids in asthma and healthy controls.
Elevated oxidative stress and impaired antioxidant defenses are increasingly recognised features of asthma. Carotenoids are potent dietary antioxidants that may protect against asthma by reducing oxidative damage.
This study aimed firstly, to characterise circulating and airway levels of carotenoids in asthma compared to healthy controls, in relation to dietary intake. Secondly, the study aimed to test whether airway lycopene defences can be improved using oral supplements. Despite similar dietary intake, whole blood levels of total carotenoids, lycopene, lutein, beta-cryptoxanthin, alpha-carotene and beta-carotene were significantly lower in asthma than controls. However, there were no differences in plasma or sputum carotenoid levels. Induced sputum carotenoid levels were significantly lower than plasma and whole blood levels, but correlated strongly with plasma levels.
Although there were no overall increases in either plasma or sputum lycopene levels following supplementation, changes in airway lycopene levels correlated with changes in plasma levels. As a conclusion whole blood, but not plasma or sputum, carotenoid levels are deficient in asthma. Plasma carotenoid levels reflect airway carotenoid levels and when plasma levels are improved using oral supplements this is reflected in the airways.
J Am Coll Nutr. 2005 Dec;24(6):448-55.
Carotenoids Improve Eye Health
Based on extensive epidemiological observation, fruits and vegetables that are a rich source of carotenoids are thought to provide health benefits by decreasing the risk of various diseases, particularly certain cancers and eye diseases. The carotenoids that have been most studied in this regard are beta-carotene, lycopene, lutein and zeaxanthin.
In part the beneficial effects of carotenoids are thought to be due to their role as antioxidants. Additionally, lutein and zeaxanthin may be protective in eye disease because they absorb damaging blue light that enters the eye. Foods sources of these compounds include a variety of fruits and vegetables although the primary sources of lycopene are tomato and tomato products. Additionally, egg yolk is a highly bioavailable source of lutein and seaxanthin. These carotenoids are available in supplement form.
Mol Aspects Med. 2005 Dec; 26 (6): 459-516. Epub 2005 Nov 23.
FOOD SOURCES - Beta carotene providing vitamin A
Food (Ãƒâ€šÃ‚µg/100g) (i.u./100g)
1. Tavani A et al, Beta Carotene intake and risk of nonfatal acute myocardial infarction in women, Eur. J. Epidemiol. 13:631-637, 1997.