The fact that beta carotene is stated to be a safe form of vitamin A suggests that vitamin A is in some way unsafe. In fact an overdose of vitamin A can lead to any one of a number of conditions, including nausea, jaundice, vomiting, abdominal pain and headaches. This vitamin is fat soluble, and so any excess is not easily washed out of the body but can build up in the tissues.
Toxicity in the liver can occur at fairly low concentrations, and the toxicity of the vitamin is increased by excessive alcohol intake. However, toxicity only occurs with vitamin A already formed such as that obtained from liver.
There are several forms of vitamin A, including the retinoid form originating from animal sources and the carotenoid forms that have a vegetable origin. Carotenoids are converted to vitamin A in the liver, but the higher the concentration of beta carotene in the body, the smaller the percentage that is converted to vitamin A, so beta carotene is a safer source of vitamin A than retinoids. It is only the finished form of vitamin A that is toxic, and beta carotene is therefore self-regulating in its production.
This vitamin is stored in the body in the form of the alcohol (retinol) and of retinyl esters. Studies have indicated that as much as 95% if the stored vitamin is in the form of the ester. The liver is responsible for releasing vitamin A to the body as it is required. One of its better known effects is on vision, and the old wives tale that carrots help you to see in the dark has an element of truth in it.
In order for it to aid vision, retinol is oxidized to the aldehyde, retinal, that forms a complex with a molecule of opsin, a light sensitive protein found in the retina. Rhodopsin, as the complex is called, is an essential component of the biochemical chain of events that lead to the perception of light. It is extremely sensitive, and enables you see in very low levels of light. In other words it is essential for good night vision, so carrots do help you to see in the dark! When a photon of light hits a molecule of rhodopsin, it leads eventually to an impulse being sent up the optic nerve to the brain.
One of its properties is its reaction to white light. When rhodopsin is exposed to white light it loses its pigmentation, and hence its photoreceptor properties and can take 30 minutes to regenerate. That is why you lose your night sight if your retina is exposed to bright light. The more rhodopsin you can generate the quicker you develop night sight.
The other biochemical processes of the vitamin include the synthesis of some glycoproteins and maintenance of normal bone density. Without vitamin A, calcium is not properly absorbed by the body and glycoproteins are involved in this process. A deficiency of vitamin A can lead to the abnormal development of bone and other health problems, so there are limits between the levels of vitamin A in the body that must be maintained: above or below these limits will lead to health problems, some of which can be extremely serious.
Most of the biochemistry of vitamin A in the liver is initiated by the presence of alcohol, and otherwise it is though to passively store the vitamin until needed when it is released into the blood. There are several ways in which the presence of alcohol allows the liver to deplete its store of retinol, but generally there are a number of enzymes that, in the presence of ethanol, can render vitamin A into a water soluble form that is excreted by the urine.
The benefits of vitamin A other than its effect on night sight and the healthy development of bone tissue, includes a powerful antioxidant effect that neutralizes free radicals that can destroy body cells. These free radicals are generated by the body's metabolism in generating energy from blood glucose, and are also created through exposure to pollutants such as cigarette smoke and traffic fumes. They are electron deficient, so when they are generated they grab an electron from tissue close by which destroys the cells involved. This can lead not only to the appearance of premature aging as the skin cells are damaged but also to serious health problems such as atherosclerosis and some forms of cancer. Vitamin A helps to protect against these by destroying the free radicals before they can do damage. It also helps build up resistance against infections by supporting the immune system.
Beta carotene is converted to vitamin A either by cleaving at the center of the molecule, or by breaking it down from one of the ends. This latter process is carried out in the small intestine, and the resultant vitamin stored in the liver in the ester form. Only a proportion of what you eat is converted to retinol ester in this way, and the more beta carotene you consume, the less is converted, so you can never suffer from an overdose of beta carotene-derived vitamin A. It might turn you yellow, but you won't suffer from excess vitamin A since the excess beta carotene is stored in your body fat, including the subcutaneous fat reserves.
Alpha carotene can also be used in the synthesis of vitamin A, but not as actively as beta carotene. The best natural sources are fruits and vegetables, especially the red, yellow and orange varieties such as carrots and apricots, and also the leafy green vegetables, although supplements are also a convenient way of maintaining your beta carotene uptake. It is a much safer supplement than straight vitamin A for the reasons explained earlier. The supplement is not useful just for its antioxidant effect, but also for its ability to protect you from excessive exposure to the sun. While not as effective as a good sun blocker, beta carotene does provide some protection.
There is no doubt that beta carotene is a safer way to maintain an adequate vitamin A uptake due to the fact that you cannot take an overdose, since an overdose of beta carotene does not translate into the same dose of vitamin A, and the change is self-regulating. It is therefore safer to obtain your vitamin A needs from colored fruits and vegetables or beta carotene supplements than from eating liver, from which the retinol is in a form that can cause damage in the event of consuming an excess.
The old adage that you should never eat polar bear livers is a true one, and certainly has a provable scientific basis, so use beta carotene as your main vitamin A source for maximum health benefits in the safest possible way.
Plant sources, however, will be more palatable for many, and may also have the advantage of providing additional anti-oxidant activity. “Carotenoids" is the generic term used to describe a large range of more than 600 pigments synthesized by plants. In modern Western diets those most frequently encountered are alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein, zeaxanthin, and lycopene.
Much attention has been focussed on alpha-carotene and beta-carotene as these can be synthesised by the body to form vitamin A, whereas this is not true of lutein, zeaxanthin, and lycopene.
Alpha and beta-carotene from plant foods are readily synthesised into vitamin A by the body. But only about 20% of dietary alpha-carotene will be used in this way, the remainder will function as a highly effective anti-oxidant in its own right, particularly within the fatty membranes of the body’s cells.
The same is true of the better known beta-carotene, except that this is much more active in terms of vitamin A provision, around 40% of dietary intake being converted into vitamin A. Surplus beta-carotene functions as an anti-oxidant in its own right, and also provides a significant boost for the immune system.
Both alpha and beta-carotene are highly fat-soluble anti-oxidants and therefore particularly effective in protecting against free radical damage to the vital fatty structures of the body’s cells, such as the membranes.
Research also suggests that high levels of carotenoids in the blood may help prevent the oxidation of Low Density Lipids (LDLs), the so-called “bad cholesterol", which is now heavily implicated in the development of the atherosclerosis, or hardening of the arteries which is a common precursor of cardio-vascular disease such as heart attack and stroke. One study of 5,000 middle aged and elderly adults showed a reduced heart attack risk of between 45-55% for people following a high beta-carotene diet, the higher figure being in respect of smokers within the group.
Numerous studies, too, have demonstrated the potential of beta-carotene as a weapon against cancer. This is probably because of its general anti-oxidant function, but also because of its proven role in keeping open the pathways between cells, which are vital to allow the immune system to kill off cancer cells in the early stages of the disease.
Conventional medical wisdom tends to accept the value of a diet rich in carotenoids but, confusingly, argues that the positive effects may be due to factors associated with such diets other than the carotenoids themselves. But alternative practitioners, of course, admit to no such doubts and are convinced of the benefits – particularly of the highly vitamin A active beta-carotene.
Whilst affirming the benefits of a diet naturally rich in carotenoids - ie in the kinds of fruits and vegetables detailed below, they insist that the maximum benefits of alpha and beta-carotene, the latter particularly, can only be secured through high dosage supplementation. Practitioners argue that studies discounting the effects of such supplementation are flawed because they have looked only at dosages too low to be effective.
And certainly the dosages they recommend appear massive – between 70,000 and 90,000 IU being proposed as the optimum to assist in the fight against both heart disease and cancer. To get this in perspective, these figures are equivalent to around 42,000 and 54,000 mcg of beta-carotene respectively, that’s to say approximately 3 to 4 cups of cooked carrots (around 13,000 mcg each).
Now, clearly an awful lot of fruit and vegetables need to be consumed to achieve the kind of intake of beta-carotene that the alternative practitioners recommend. And it also needs to be noted that optimum absorption of carotenes depends on the presence of a reasonable amount of dietary fat.
So chopping, pureeing, and cooking carotenoid rich vegetables in oil is the ideal way to maximise the bio-availability of these nutrients. But it’s neither convenient nor appetising. And whilst an 8 fl oz glass of carrot juice provides around 22,000 mcg (37,000 IU) of beta-carotene, would you consider giving up your morning coffee in its favour? Me neither!
But apart from the convenience, another point in favour of supplementation is that it appears not to be harmful in any likely dosage. In fact the only side effect to have been noted even from doses as high as 250,000 IU has been a benign, if unflattering, “fake tan" skin pigmentation, which very quickly vanishes upon the reduction of the dose.
So it appears that supplementation may do some good, is extremely unlikely to do any harm, but for best results should be taken as part of a normal daily diet already well supplied with carotenoid rich foods.
Both Darrell Miller & Steve Smith are contributors for EditorialToday. The above articles have been edited for relevancy and timeliness. All write-ups, reviews, tips and guides published by EditorialToday.com and its partners or affiliates are for informational purposes only. They should not be used for any legal or any other type of advice. We do not endorse any author, contributor, writer or article posted by our team.
Darrell Miller has sinced written about articles on various topics from Search Engine Marketing, Arthritis Signs and Anti Oxidant. More information on vitamin A can protect and heal the body at VitaNet ?, LLC Health Food Store.. Darrell Miller's top article generates over 90500 views. to your Favourites.
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