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Beta Carotene Supplements & Quality Beta Carotene Vitamin Information cncahealth.com | Beta Carotene drmyattswellnessclub.com | MacularProtect Complete-S: AREDS Formula with Multivitamin,... sciencebasedhealth.com | Vitamins And Vision Loss Vitamin E Vitamin C Beta Carotene Zinc Copper healthbulletin.org |
β-Carotene is an organic compound - a terpenoid, a red-orange pigment abundant in plants and fruits. As a carotene with beta-rings at both ends, it is the most common form of carotene. It is a precursor (inactive form) of vitamin A.[3] Being highly conjugated, it is deeply colored, and as a hydrocarbon lacking functional groups, it is very lipophilic. The structure was deduced by Karrer et al.[4] In nature, β-carotene is a precursor to vitamin A via the action of beta-carotene 15,15'-monooxygenase. β-Carotene is also the substance in carrots that colours them orange. β-Carotene is biosynthesized from geranylgeranyl pyrophosphate.[3] Isolation of beta-carotene from carotenoids abundant fruits is commonly done, using colume chromatography. The separation of beta-carotene from the mixture of carotenoids is based on the polarity of a compound. Beta-carotene is a non-polar compound, so it is separated with a non-polar solvent such as hexane.[5] Being highly conjugated, it is deeply colored, and as a hydrocarbon lacking functional groups, it is very lipophilic.
[edit] Pro-vitamin A activityPlant carotenoids are the primary dietary source of pro-vitamin A worldwide, with β-carotene as the most well-known pro-vitamin A carotenoid. Others inlcude α-carotene and β-cryptoxanthin. Carotenoids are absorbed into the small intestine by passive diffusion. One molecule of β-carotene can be cleaved by a specific intestinal enzyme into two molecules of vitamin A. Absorption efficiency is estimated to be between 9-22%. The absorption and conversion of carotenoids may depend on the form that the β-carotene is in (cooked vs. raw vegetables, in a supplement), intake of fats and oils at the same time, and the current levels of vitamin A and β-carotene. Researchers list the following factors that determine the pro-vitamin A activity of carotenoids: [6]
[edit] Symmetric/Asymmetric CleavageThe chain between two toluene rings either symmetrically or asymmetrically cleave. Symmetric cleavage is done by an enzyme called beta-carotene-15,15'-dioxygenase in human body. The symmetric cleavage gives two equivalent retinal and each retinal further reacts to give retinol(aka, vitamin A) and retinoic acid. Beta-carotene is also asymmetrically cleaved into two asymmetric products. The products of asymmetric cleavage is beta-apocarotenal(8',10',12'). Asymmetric cleavage reduces the level of retinoic acid significantly.[7] [edit] Conversion factorsUntil recently, vitamin A activity in foods was expressed as international units (IU). This is still the measurement generally used on food and supplement labels. However, it is difficult to calculate the total vitamin A activity in the diet in terms of IU, because both the absorption and conversion of carotenoids, as compared with retinol, are variable. The unit retinol equivalent (RE) was developed by the Food and Agriculture Organization of the United Nations/World Health Organization (FAO/WHO) in 1967[8]. More recently in 2001, the US Institute of Medicine proposed retinol activity equivalents (RAE) for their Dietary Reference Intakes[9]. [edit] International Units1 RE = 3.33 IU vitamin A activity from retinol 1 RE = 10 IU vitamin A activity from β-carotene [edit] Retinol Equivalents (REs)1 RE = 1 µg retinol 1 RE = 6 µg β-carotene 1 RE = 12 µg other provitamin A carotenoids [edit] Retinol Activity Equivalents (RAEs)1 RAE = 1 µg retinol 1 RAE = 2 µg all-trans-β-carotene as a supplement 1 RAE = 12 µg of all-trans-β-carotene in a food matrix 1 RAE = 24 µg other provitamin A carotenes in a food matrix [edit] Sources in the dietβ-Carotene contributes to the orange color of many different fruits and vegetables. Vietnamese gac (Momordica Cochinchinensis Spreng.) and crude palm oil are particularly rich sources, as are yellow and orange fruits, such as mangoes and papayas, orange root vegetables such as carrots and yams and in green leafy vegetables such as spinach, kale, sweet potato leaves, and sweet gourd leaves. Vietnam gac and crude palm oil have by far the highest content of β-carotene of any known fruit or vegetable, 10 times higher than carrots for example. However, Gac is quite rare and unknown outside its native region of SE Asia, and crude palm oil is typically processed to remove the cartenoids before sale to improve the color and clarity. The average daily intake of β-carotene is in the range 2-7 mg, as estimated from a pooled analysis of 500,000 women living in the USA, Canada and some European countries. [10] The U.S. Department of Agriculture lists the following 10 foods to have the highest β-carotene content per serving.[11]
[edit] Side effectsThe most common side effect of excessive β-carotene consumption is carotenodermia, a harmless condition that presents as a conspicuous orange skin tint arising from deposition of the carotenoid in the outermost layer of the epidermis[12]. Chronic, high doses of β-carotene supplements have been associated with increased rate of lung cancer among those who smoke.[13] Additionally, supplemental beta-carotene may increase the risk of prostate cancer, intracerebral hemorrhage, and cardiovascular and total mortality in people who smoke cigarettes or have a history of high-level exposure to asbestos. Beta-carotene from foods does not seem to have this effect.[14] [edit] Beta-carotene and Lung cancer among those who smokeCigarette smoke increases the asymmetric cleavage of beta-carotene, decreasing the level of retinoic acid significantly. When retinoic acid is liganded to RAR-beta(Retinoic Acid Receptor), the complex acts as AP1(activator protein 1) binding site. AP1 is a protein which turns on cell proliferation when binds to its binding site on DNA. Therefore, the presence of retinoic acid prevents AP1 from binding to its binding site on DNA. AP1 is no longer expressed, and cell proliferation does not occur. However, no lung damage has been detected in those who are exposed to cigarette smoke and physiologic dose beta-carotene(6mg) in contrast to pharmacologic dose (30mg). Therefore, the oncology from beta-carotene is based on both cigarette smoke and daily doses of beta-carotene.[15] [edit] See also[edit] References
[edit] External links
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