Carotenoids are defined as "Any of a class or group of yellow to red pigments, including the carotenes and the xanthophylls, found especially in plants, algae, and photosynthetic bacteria and certain animal tissues. Carotenoids generally consist of conjoined units of the hydrocarbon isoprene, with alternating single and double bonds."
Carotenoids represent one of the most widespread groups of naturally occurring pigments. They are organic and are found in the chloroplasts and chromoplasts of plants and some photosynthetic organisms like algae, some bacteria, and some fungi. Carotenoids generally cannot be manufactured by species in the animal kingdom, so animals must obtain carotenoids from their diets.
These compounds are largely responsible for the red, yellow, and orange colour of fruits and vegetables, and are also found in many dark green vegetables. When chlorophyll is present, as in dark green vegetables, the pigment of the carotenoids is often not obvious, due to masking by the chlorophyll. When chlorophyll is not present, as in young foliage and also dying deciduous foliage (such as autumn leaves), the yellows, reds, and orange of the carotenoids are predominant. For the same reason, carotenoid colours often predominate in ripe fruit (eg oranges, tomatoes, bananas), after being unmasked by the disappearance of chlorophyll.
There are over 600 known carotenoids. They are split into two classes:
· Xanthophylls, which contain oxygen. These include lutein and zeaxanthin.
· Carotenes which are purely hydrocarbons, and contain no oxygen. These include alpha-carotene, beta-carotene and lycopene.
All carotenoids are tetraterpenoids, meaning that they are produced from eight isoprene molecules and contain 40 carbon atoms. Carotenoids in general absorb blue light. They serve two key roles in plants and algae:
· They absorb light energy for use in photosynthesis.
· They protect chlorophyll from photo-damage.
Probably the most well-known carotenoid is beta-carotene, which is how the group gained the name, 'carotenoids'.
Functions of Carotenoids in Humans
· Preventing Vitamin A Deficiency
Certain members of the carotenoid family, approximately 50 of the known 600, are called 'provitamin A' compounds because the body can convert them into retinol, retinal and retinoic acid, active forms of vitamin A.
As a result, foods that contain these carotenoids can help prevent vitamin A deficiency.
Vitamin A has multiple functions. It is important for:
Ø Growth and development
Ø Maintenance of the immune system
Ø Good vision
Ø Bone metabolism, red cell formation, skin and cellular health
Ø Antioxidant activity
Vitamin A can be found in two principal forms in foods:
Ø Preformed vitamin A- retinol and its esterified form, retinyl ester. This form of vitamin A is absorbed when eating animal food sources, including dairy products, fish and meat (especially liver), and is a yellow fat-soluble substance.
Ø Provitamin A carotenoids. The most commonly consumed provitamin A carotenoids are beta-carotene, alpha-carotene, gamma-carotene, and beta-cryptoxanthin, of which beta-carotene is the most important.
The 10 foods highest in vitamin A obtained from carotenoids (see www.healthaliciousness.com) are
Ø Paprika, red pepper, cayenne, chili powder
Ø Sweet potatoes, especially the orange coloured ones
Ø Dark leafy vegetables, especially kale, spinach and collards
Ø Butternut squash
Ø Dried herbs, for example dried parsley, basil, dill and oregano
Ø Lettuce, especially dark coloured
Ø Dried apricots
Ø Cantaloupe (rockmelon) and other yellow-orange melons
· Antioxidant and Immune-Enhancing Activity
Carotenoids are powerful antioxidants, protecting the cells of the body from damage caused by free radicals. For a full discussion on the subject of free radicals and antioxidants, see my January 2007 newsletter Free Radicals - Antioxidants.
Carotenoids, and specifically beta-carotene, are believed to enhance the function of the immune system. Their role is set out in my June 2006 newsletter The Immune System and Immunity, which deals with and describes in detail the immune system and its function in health.
Some carotenoids, such as lycopene, do not convert to vitamin A. Lycopene is the orange-red pigment found, for example, in tomatoes and watermelon, and is a strong antioxidant even more powerful than beta-carotene.
· Protection against Cancer
Carotenoids have a definite role in cancer prevention. This is mainly as a result of their powerful antioxidant properties. Research shows that people who consume a lot of foods that are rich in beta-carotene are less likely to develop lung cancer, even among smokers.
It should be noted that taking a beta-carotene supplement in a pill form does not give the same effect as obtaining it from food sources. This is because when the food is a source of beta-carotene, it is consumed with a combination of multiple (possibly hundreds) other carotenoids. It is the combined synergistic effect that gives protection against cancer, not just the isolated single beta-carotene.
Lutein, zeaxanthin, lycopene, and alpha-carotene show evidence of being significantly more protective than beta-carotene against lung and some other cancers.
There is abundant evidence that lycopene in particular helps reduce the incidence of prostate cancer.
Many experts now believe that the protective effect of carotenoids against cancer depends on the timing of when you take them (in foods). They are best at prevention rather than as a treatment once the precancerous changes are taking place. The antioxidant activity can prevent free radicals from damaging cells and the DNA inside the cells, both of which can start cancerous growth. This is 'primary protection from cancer' - cancer never gets started.
Toxicity Symptoms for Carotenes
A sign of excessive consumption of beta-carotene is a yellowish discolouration of the skin, most often occurring in the palms of the hands and the soles of the feet. This condition is called carotenodermia, and is reversible and harmless. Excessive consumption of lycopene can cause a deep orange discolouration of the skin. Like carotenodermia, lycopenodermia is harmless.
There are no other toxic side effects with high intake of carotenoid-containing foods.
Carotenoids are vital to overall health.
It is recommended that the ideal diet is one which is dominantly plant-based, and that 75%-85% of the food consumed should be alkali-forming. See my September 2005 newsletter Acid/Alkali Balance - The Ideal Diet and my March 2009 newsletter Foods for Health. Such a diet will ensure adequate intake of the all important carotenoids, with the health benefits that will result.
*Copyright 2013: The Huntly Centre.
Disclaimer: All material in the huntlycentre.com.au website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.
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