Carotenoids

DESCRIPTION

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:
1 µg (3.33 i.u.) Vitamin A = 6 µg Beta Carotene = 12 µg other carotene precursors

Beta Carotene :
The most abundant carotenoid in the diet, it is the most effective at converting to Vitamin A . Numerous studies support its role in human health. High intakes of Beta Carotene have been associated with a lower risk of many various cancers and more recently Beta Carotene supplements significantly enhanced skin protection against UV light when combined with topical sunscreens. High intakes (exceeding 20mg a day) are best avoided by long term heavy smokers.
Best food sources: carrots, peaches, apricots, spinach and cantaloupe.

Alpha carotene:
Found in abundance in the diet. Research has shown an association between a low intake of vegetables and alpha carotene and a higher incidence of lung cancer among smokers.
Best food sources: carrots and pumpkins.

Lycopene:
Probably the most effective scavenger of singlet oxygen (a type of free radical). Research suggests that consumption of lycopene rich foods may lower the risk of prostate and stomach disease.
Best food sources: tomatoes, watermelon, pink grapefruit.

Lutein and Zeaxanthin:
These are yellow carotenoids found in the Eyes. Studies show a potential link between a diet high in lutein and zeaxanthin and a lower risk of Age-related Macular Degeneration (AMD), a serious eye disease which can cause irreversible blindness.
Best food sources: spinach, red pepper, peas, kale, broccoli and celery. (Note: the chloropyll in green vegetables masks the yellow of lutein and zeaxanthin.)

Cryptoxanthin:
Possibly one of the least well known of the common carotenoids found in food. One study found women with cervical cancer to have very low blood levels of this carotenoid.
Best sources: oranges, papaya, peaches and tangerines.

FUNCTIONS

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 ‘free radical’ 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 body’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

Deficiency symptoms of beta carotene are the same as for Vitamin A .

REQUIREMENTS

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.

SUPPLEMENTAL USES

Carotenoids can be taken purely for their Vitamin A activity, but the nutrients’ 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).

SAFETY

Beta Carotene is an extremely safe form of Vitamin A , because at very high levels of intake, the body’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.

INTERACTIONS AND CONTRA-INDICATIONS

Smokers:
Smokers are advised not to take individual high level beta carotene supplements.

Those who work with or have been exposed to asbestos are advised to avoid Beta Carotene supplements (3,4).

FOOD SOURCES

Beta Carotene providing Vitamin A

Food (µg/100g) (i.u./100g)
Carrots (old) 6667 12000
Spinach 3333 6000
Sweet potato 2233 4000
Apricots, dried 2000 3600
Watercress 1667 3000
Mango 667 1200
Tomatoes 333 600
Cabbage 167 300
Peas, frozen 167 300
Potatoes 0 0

REFERENCES

1. Tavani A et al, Beta Carotene intake and risk of nonfatal acute myocardial infarction in women, Eur. J. Epidemiol. 13:631-637, 1997.
2. "Handbook of Dietary Supplements", Pamela Mason, Blackwell Science, 1995.
3. Anon, The effect of Vitamin E and Beta Carotene on the incidence of lung cancer and other cancers in male smokers. The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. New England J Medicine, 330:1029-1035, 1994.
4. Omenn GS et al. Effects of a combination of Beta Carotene and Vitamin A on lung cancer and cardiovascular disease. New England J Medicine, 334:1150-1155, 1996.