Carotenoids are a class of fat-soluble pigments found primarily in plants, algae and photosynthetic bacteria, where they play a role in the photosynthetic process. They can occur in non-photosynthetic bacteria and fungi as well. One of their functions in plants is to protect them against oxidation. Many of the yellow-orange-red colours of fruits, flowers and plant leaves are caused by carotenoids.
The aroma of many flowers and fruits (as rose, tobacco, grape) is due to chemical breakdown of carotenoids. In the perfume industry, such compounds are widely used.
Technically there is a difference between so-called hydrocarbon carotenoids, which are called carotenes – they do not contain oxygen; and oxygenated derivatives of the same hydrocarbons, which are known as xanthophylls – they do contain oxygen.
Xanthophylls are the most common source of yellow in leaves. They are always there, although masked by the green chlorophyll, and become visible only when the chlorophyll has been degraded. They have the ability to absorb certain wavelengths of the light that the chlorophyll cannot absorb. There they protect the plant from sun-related damage, and they absorb blue light for the photosynthesis.
Some animals get red to yellow colours by carotenoids. Contrary to most other pigments they have, they cannot produce carotenoids themselves, but need to obtain them through their diet. If they ingest the wrong food, they lose the colour. Birds in captivity, for instance, can lose the colour of their beak; or, as with flamingoes, the colour of their feathers.
Bound to a protein, carotenoids can give green or blue colours - as with the lobster.
The skin of humans who eat a lot of carotene can develop an orange tone. This is a harmless condition; possibly it increases protection against sun-related damage (oxidation).
Carotenoids have a number of health promoting qualities. Several carotenes - most notably beta carotene, alpha carotene, gamma carotene and beta-cryptoxanthin - can serve as pro-vitamin A. That means that enzymes and intestinal bacteria can convert some of them to vitamin A, while the rest enters the blood without that conversion. The vitamin A is then stored in the liver. But note that the intestinal microflora must be well maintained for this to work. Otherwise there will be no conversion and no vitamin A.
The macula lutea of the eye; and the corpus luteum, a structure in the ovary of mammals [related to hormones and reproduction] contain carotenoids which give them their colour and have important protecting functions.
Another detail to remember is that carotenoids are fat-soluble, so you must take them together with some fat. Otherwise you will not absorb them.
Some of the most important carotenoids are:
Beta-carotene; in carrots, spinach, peaches, apricots, most green or orange coloured fruits and vegetables; it is the typical provitamin A.
Alpha-carotene; in carrots, pumpkin, tomatoes, green beans, sweet potatoes, squash, broccoli, kale, cantaloupe, Brussels sprouts, kiwi, spinach, mangoes, squash, and spinach, and red and yellow peppers. Has provitamin A potential.
Gamma-carotene; has provitamin A potential.
Cryptoxanthin; in papaya, oranges, tangerines, peaches, nectarines, corn and watermelon; like most carotenoids it is related to protection against age-related disease, and against eye degeneration. Has provitamin A potential.
Lycopene; in tomatoes and rose hips; has shown to have a strong preventive effect against prostate enlargement, possibly curing as well.
Canthaxanthin: clinically proved to retard growth of cancer. This is the carotenoid that gives flamingos their pink colour. They get it from shellfish in their diet. It can be found in certain mushrooms as well. As a supplement, some people take it to get artificial tan, to get a bronze-coloured skin.
Neoxanthin: clinically proved to inhibit tumour growth.
Lutein and zeaxanthin; see previous article Lutein & Zeaxanthin: Nutrients that Protect Your Eyes from Ageing, in which I discuss these two carotenoids in detail.
Astaxanthin, in salmon and other seafoods, is another naturally occurring xanthophyll with potent antioxidant properties. Successful results have been reported in the treatment of arthritis.
Capsanthin and capsorubin, the red of paprika (Capsicum annuum) and other capsicum species. Capsanthin is an antioxidant and has proven anti-tumour effects.
Taraxanthin, giving the dandelion (Taraxacum officinale) its yellow colour. A good antioxidant.
Beta-Carotene & Smokers
A warning. Danger with high dose beta-carotene, in itself a strong anti-oxidant, has been indicated for heavy smokers and drinkers, who can get an increased cancer risk by it. This is not yet properly understood, but it might have to do with breakdown products.
What we know:
- Beta carotene is an antioxidant and it has shown to reduce the risk for several forms of cancer.
- A few studies have shown that beta carotene supplementation can increase the lung cancer risk for smokers and heavy drinkers. Although there are always theories circulating, the mechanism behind this is not yet understood.
- Nothing indicates that beta carotene would increase the cancer risk for non-smokers and non-drinkers.
My opinion:
High dose supplementation of only one or a few nutrients is always risky. Nutrients are interacting with one another, protecting and supporting each other. Beta carotene does never occur isolated in nature, but is mixed with other carotenoids and non-carotenoid nutrients.
I suggest that supplementation should always contain many carotenoids, as well as other nutrients. A multivitamin with a moderate amount of beta carotene (but lacking other carotenoids) should be safe too. If you are a smoker, you might prefer to avoid the latter though; until the mechanism behind the results of these studies is properly understood.
There is no reason to fear natural carotene sources, such as carrot juice. There the beta carotene occurs in its real environment, combined with other nutrients in a natural way; and the dose will never grow as high as it might with supplementation.
(The article is based on material previously published in Meriondho Leo, and in my e-book “Nutrients & Dietary Supplements”, 2019.)
Previous articles on nutrients & supplements:
Oxygen: Life & Death – A Balanced View on Antioxidants
Understanding Dietary Fats Part 1 (of 2)
Understanding Dietary Fats Part 2 (of 2)
Why Dietary Supplements are Needed
Supplements, Getting Them Right: Some Points to Consider
The Importance of Dietary Solvents
Salicylic Acid: Is Aspirin a Vitamin?
Lutein & Zeaxanthin: Nutrients that Protect Your Eyes from Ageing
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yes, I agree that high dose of one supplementation of one of the nutrient is risky even deficiency and over dose both are risky . Very helpful and informatic topic. .