Beta-Carotene: An Overview
β-carotene is a chemical that has been classified as a terpenoid in the plant world. Terpenoids are a sector of organic chemicals. They have structures which include five-carbon isoprene units, but vary significantly in shape and other elements of structure. It is a well known fact that the compound beta-carotene contributes to the pigmentation of many fruits and vegetables. Orange pigmentation in foods like carrots is the best known visual effect of carotene, but the compound also contributes to green, yellow, and red coloring in naturally occurring substances. Colors of fall foliage are influenced by the presence of carotene in the absence of chlorophyll.
A forerunner of vitamin A production, β-Carotene is converted to vitamin A through the activity of β-Carotene enzyme 15, 15′-monoxygenase. β-Carotene can either be isolated from plants or produced synthetically. The plant isolation method of extracting carotene is normally completed through column chromatography. In this process, compound polarity based on a non-polar solvent is used to separate carotenoids from other compounds in fruits rich in β-Carotene. Repelled by lipids and without function groups, the hydrocarbon is easy to find due to both of these factors and the dark pigmentation that marks it. The most common sources for extracting β-carotene are algae, fungi, and crude palm oil. In contrast, the β-Carotene synthetic production method differs greatly. To produce the dually beta-ring capped compound, geranylgeranyl pyrophosphate is biosynthetically altered into β-Carotene, the most commonly occurring carotenoid in nature.
Absorption of Vitamin A through β-Carotene
Because β-Carotene is a form of pro-vitamin A, it has great nutritional value. The compound uses passive diffusion to gain absorption into the body by means of the small intestine. The absorption efficiency of vitamin A from β-Carotene can vary wildly, and is generally believed to range between nine and twenty-two percent absorption. The enzyme 15, 15′-monoxygenase is used to cleave a single molecule of β-Carotene into a final result of two molecules of vitamin A. After this cleaving of the molecule is complete, vitamin A can be used to complete its benefits. Absorption may actually rely on the method used to prepare β-Carotene.
Whether the vitamin is obtained from a vegetable or a supplement, preparation can alter absorption. Certain studies even point to the idea that the vitamin can only be efficiently absorbed when it starts out in a natural form. However, these reports remain inconclusive. Other factors that affect the absorption of β-Carotene include whether or not lipids are consumed concurrently and how high bodily levels of both vitamin A and β-Carotene are at the point of absorption. Amount of β-Carotene in the food eaten, matrix properties, the linkage between molecules, carotenoid species, and genetics can also play into this complicated matter. A possibility of these factors interacting with each other increases variability of absorption to an even greater degree.
Differences in β-Carotene Cleavage Affect Yield
The chain linking the double cyclohexyls rings can determine differences in the products of a conversion reaction from β-Carotene to vitamin A. This is due to the fact that the chain may cleave in two ways. In the first, known as symmetric cleavage, beta-carotene-15,15′-dioxygenase cleaves the β-Carotene into two retinal molecules that are equal in size. Both of these retinal molecules react to form both vitamin A and retinoic acid. When β-Carotene is cleaved asymmetrically, producing two asymmetrical products. This produces β-apocarotenal (8′,10′,12′) and lessened amounts of retinoic acid.
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Using Conversion to Discover the Amount of Vitamin A Produced by Foods
Conversion factors can be incredibly important in determining how much vitamin A is in a given food. Previously, vitamin A activity was measured in international units, also known as IU. Although this scale is still used on most food and supplement labels, calculating in IU is ineffective. As mentioned above, the absorption rate of vitamin A is variable, as is the conversion rate. For this reason, a brand new measure was created by international organization FAO/WHO back in 1967. This unit, retinol equivalent, or RE, shows a much more accurate representation of the amount of vitamin A in a food. In the year 2001, another measure was created to try and accurately express the amount of vitamin A in a food. The US Institute of Medicine set forth a proposal for using this measure, retinol activity equivalents (RAE) for use in determining vitamin A intake. The following conversion factors can aid in determining what the non-interchangeable units of measurements mean in relation to each other.
To convert from IU to RE, one retinol equivalent is equal to 3.33 IU of vitamin A activity. However, this measurement is used for determinations from retinol only. For determinations from beta-carotene, an RE is set equivalent to 10 IU of activity. Canadian calculations differ slightly, claiming that an RE from β-carotene is equal to 6.667 IU.
In retinol equivalents, 1 RE is equal to a microgram of retinol. Six micrograms of β-carotene equals an RE as well. Canada has set their regulations so that an RE equals 2 micrograms of β-carotene.
Retinol Activity Equivalents, or RAEs, are the newest form of measurement. An RAE, like an RE, equals a microgram of retinol. Like the Canadian standard, 2 micrograms of supplement β-carotene amounts to an RAE. However, if an RAE is coming from a food source, it is set equal to 12 micrograms of β-carotene. All other pro vitamin A carotenes have 24 micrograms in an RAE if they are derived from a food matrix.
How to Obtain β-carotene from a Diet
An orange color in a fruit or vegetable is the first hint to finding β-carotene in a food. Among the richest sources of β-carotene are the rare (and difficult to find) Vietnamese gac and crude palm oil. Palm oil processing often removes the nutrient in order to improve clarity of the substance. The gac is unknown to people who do not live in South East Asia. These sources have ten times the amount of β-carotene as carrots, however, and would be great sources if they were more readily available.
More common sources of β-carotene can include fruits, such as mangoes and papayas. Orange root vegetables (think carrots and yams) are another tasty source of β-carotene. Additionally, leafy greens, the go-to veggies for many different vitamins and nutrients also contain β-carotene. These foods include the ever popular kale and spinach (both members of the lucrative Brassica group) and the more obscure sweet gourd and sweet potato leaves. According to a survey of people living in the United States of America, Canada, and several other European countries, most women absorb between two and seven milligrams of β-carotene a day, on average.
The USDA has compiled a top ten list of the foods richest in β-carotene per serving. Nearing the top of the list, carrot juice has 236 grams per a one cup serving. This amounts to 22 mg of carotene per serving, and 9.3 mg per one hundred mg. Oddly enough, unsalted canned pumpkin has closely follows. There are 245 grams in a serving of canned pumpkin. A cup of the mushy food yields seventeen mg of β-carotene.
This is a hefty 6.9 mg of of β-carotene per hundred grams. Cooking method does make a difference, as exemplified by the case study of the sweet potato. Baked with the skin on, one potato that weighs approximately 146 grams yields 16.8 mg per serving, or 11.5 mg per 100 g. If the same potato is boiled without the skin, it weighs in at 156 grams but yields 14.7 mg per serving and 9.4 mg/100 g. In a third case, 255 grams of canned, vacuum packed sweet potato results in a cup of potatoes containing 12.2 mg per serving and 4.8 grams per hundred grams. Carrot preparation holds with this trend as well.
Boiled carrots that are cooked from fresh have 156 grams in a serving. In this cup of carrots, there are 13.0 mg of β-carotene and 7.2 milligrams per hundred grams. Carrots cooked in the same manner from frozen amount to 146 g/per serving. A cup of these carrots contains a slightly lesser amount of β-carotene, at 12.0 milligrams per cup and 8.2 milligrams per hundred grams of the food. The storage method of a food does not always follow by the same rules, however. Frozen and cooked spinach weighing 190 g per cup produces 13.8 milligrams in a serving, and 7.2 per hundred grams. When spinach is canned and drained, a cup weighing 214 grams has 12.6 mg of β-carotene per serving and 5.9 per hundred grams. This is a significant difference that cannot be overlooked. Boiled collards round out the end of the list. One hundred seventy grams per serving makes a cup containing 11.6 mg, which figures out of 6.8 mg per serving.
There are other sources besides vegetables to receive β-carotene and Vitamin A. Foods like grapefruit, fish, apricots, broccoli, milk, and eggs can solve a deficiency of the vitamin. Cilantro, turnip greens, cantaloupe, and romaine lettuce all contain the compound β-carotene. It is easy to find a source of β-carotene for almost everyone.
Uses for Beta-carotene
Beta-carotene is an essential supplement in a diet for many reasons. The vitamin A produced has many beneficial effects on the body. Besides protecting cells from dangerous free radicals, carotene can lend a hand in preventing the onset of heart disease and cancer, two of the deadliest diseases known to man. Preventing cancer is done through increasing the effectiveness of communication between cells. This better communication leads to less errors in the replication of DNA, and thus, less occurrences of malignant cells. A requirement for eye health, beta-carotene can fend against debilitating macular degeneration and help to slow cataract onset and progression.
Beta carotene shields dermal tissues from sunburn. Additionally, it can help with controlling and preventing conditions as diverse as asthma and arthritis, psoriasis and Parkinson’s disease, depression and high blood pressure. There are suggested links between alleviation of the symptoms of Acquired Immunodeficiency Syndrome (AIDS) and β-carotene. Cervical cancer, chlamydia,and cervical dysplasia might all experience increased prevention rates from the implementation of β-carotene in a diet. From photo-sensitivity to yeast infections, beta carotene has been suggested to offer help. Beta carotene can even help with infertility. A deficiency of the nutrient is dangerous.
Deficiency of β-carotene may be associated with a resulting deficiency in vitamin A. The repercussions of such a deficiency include night blindness, dry eye, inability to heal, white spots on the interior of eyelids, and even corneal issues that can result in blindness. Other symptoms include weight loss, acne, fatigue, insomnia, abscesses in the ear and respiratory infections.
In some cases a rare genetic disorder called erythropoietic protoporphyria can be aided by supplementation of β-carotene. β-carotene is useful in this skin disorder because the pophyrin-heme metabolism in these individuals has been disrupted. This leads to several physical manifestations, including extreme photo-sensitivity. Commercially available synthetic β-carotene has been FDA approved to treat this photo-sensitivity, offering protection from the sun.
Recommended Dosages of β-carotene
Consuming the recommended amount of fruit and vegetables (five apiece) every day should eliminate the need for a supplement for β-carotene. However, if this is not possible, it is recommended that adults consume from 6 to 15 mg of β-carotene daily. Children, on the other hand, should take 3-6 mg per day. Breastfeeding mothers should implement a slight increase in β-carotene. A healthy amount of fat in the diet aids in the absorption of β-carotene. Due to side effects, smokers should watch their intake of β-carotene supplements, capping intake at 20 mg daily to avoid serious health issues. Pregnant women should also make sure not to take in toxic levels of β-carotene, as this has been linked to some birth defects.
Side Effects of β-carotene that Should Be Taken Seriously
Like almost all substances, β-carotene has harmless and serious side effects alike. The most prevalent of the side effects is a result of toxicity. The condition known as carotenodermia is characterized by a shocking orange skin tint. The increased pigmentation can make a person appear a yellowish orange color. This condition results from carotenoid being deposited in the upper layer of the epidermis. While the condition is currently deemed to be harmless, the condition can be embarrassing because of the conspicuous state of an unnatural skin color. Another effect of taking high doses of β-carotene supplements is the occurrence of lung cancer in smokers.
Studies have suggested that, when taken in supplement form, β-carotene can increase the risk of cancer in those people who smoke cigarettes.
There are several theories which attempt to explain the elusive origin of this counter-intuitive phenomenon. One of the most popular explanations concerns the way that retinoic acid ligands to Retinoic Acid Receptor beta, also known as RAR-beta. This complex often binds to Activator Protein 1 (AP1). Downstream events of DNA transcription are affected by this change. Normally, AP1 binds to DNA, promoting the proliferation of cells. However, when retinoic acid enters the equation, RAR-beta inhibits AP1 from binding to DNA. When this happens, AP1 is not present when it becomes time for the cell to begin DNA transcription. Cells cannot proliferate normally in these circumstances.
As mentioned above, β-carotene is sometimes cleaved asymmetrically. This increased asymmetric cleavage, as this article has mentioned, leads to a decreased level of retinoic acid. Smoking cigarettes, it turns out, increases the probability of asymmetrical cleavage of β-carotene.
Increased cell proliferation in smokers leads to a higher probability of the development of malignant cells. This could be a plausible explanation for the number in studies about smoking and β-carotene. The higher degree of lung cancer in smokers who consume large amounts of β-carotene supplements is unmistakable. A secondary theory concerns another substance created from the breakdown of β-carotene: trans-beta-apo-8′-carotenol, known as apocarotenal.
This substance has been proven to not only induce mutations and but also to become genotoxic to cell cultures that do not respond to beta-carotene. Neither of these theories has been tested significantly enough to induce a level of confidence in the cause of the smoking/β-carotene occurrence of lung cancer.
Although the mechanism is unknown, it is known that only supplement forms of β-carotene show this increased risk. No link has been shown between smokers who receive β-carotene from natural food sources. The pharmacological sources of the vitamin, however are dangerous for the lungs of smokers. Smokers also face an increased risk of cardiovascular/total mortality, prostate cancer, and intracerebral hemorrhage. This risk also exists for people who have experienced exposure to asbestos.
Extras: The Good Side Effects of β-carotene
Using fish oil as a supplement can result in many positive effects in heart health and longevity. However, consumption of fish oil also shows oxidative stress. β-carotene can help to lower this stress and even augment the positive plasma triglyceride lowering properties of fish oil.
In babies, iron supplements are essential, but also lower the levels of plasma vitamin A. A β-carotene supplement in infants with marginal vitamin A concentrations can help to improve the production of vitamin A and avoid the devastating effects of vitamin A deficiency.
Other positive side effects of β-carotene include healthier skin, including acne reduction, better formation of teeth and other growth tissues, increased immunodeficiency, maintenance of the urinary and digestive tracts, and even a sharper sense of taste. All of these benefits add up to a good reputation for β-carotene.
The History of β-carotene
β-carotene has a long history. The chemical was first noticed in casual observation of the outside world. Scientists have always held a fascination with what chemicals could cause fruits and vegetables to be bright with such vibrant colors. Studies on β-carotene started springing up in the early 1800s, but have continued up until the present day. β-carotene was successfully isolated in 1831 by a scientist named Wachenroder. Wachenroder named the compound carotene after isolating the compound from roots of carrots. The structure of β-carotene, however, was still a mystery. The chemical formula of β-carotene C40H56 was first discovered in 1907.
β-carotene is interesting in that it was the first pro-vitamin discovered. Scientist Karrer won a Nobel prize for his work on β-carotene. The pro-vitamin was first manufactured commercially in the 1950s. In the nineteen-eighties, the antioxidant properties of β-carotene were discovered, leading to many studies on its effect on cancer. Humanity is still studying the effects of β-carotene and its possible positive and negative effects in our lives.
A polar bear liver contains, in every 500 grams of weight, contains 9 million IU of β-carotene. Ingesting this amount would be lethal, resulting in headaches, hairloss, diarrhea, spleen and liver enlargement, loss in vision and drowsiness. This can be counted as yet another great reason to avoid eating polar bear liver.
Cooking at high temperatures or with copper and iron utensils can lead to a decrease in β-carotene in food. This can also occur if food is soaked in water for extended periods of time.
The blue green algae that flamingos eat is high in β-carotene. The amount of β-carotene in the algae causes the familiar pink pigmentation of flamingos. If flamingos are fed a diet low in β-carotene, they return to white, their natural color.
Rice can be modified to contain β-carotene, this technique is being used to supplement diets in poverty striken areas to prevent vitamin A deficiency.