| act that beta carotene is stated to be a safe | | | | presence of alcohol allows the liver to deplete its |
| form of vitamin A suggests that vitamin A is in | | | | store of retinol, but generally there are a number |
| some way unsafe. In fact an overdose of vitamin | | | | of enzymes that, in the presence of ethanol, can |
| A can lead to any one of a number of conditions, | | | | render vitamin A into a water soluble form that is |
| including nausea, jaundice, vomiting, abdominal pain | | | | excreted by the urine. |
| and headaches. This vitamin is fat soluble, and so | | | | The benefits of vitamin A other than its effect on |
| any excess is not easily washed out of the body | | | | night sight and the healthy development of bone |
| but can build up in the tissues. | | | | tissue, includes a powerful antioxidant effect that |
| Toxicity in the liver can occur at fairly low | | | | neutralizes free radicals that can destroy body |
| concentrations, and the toxicity of the vitamin is | | | | cells. These free radicals are generated by the |
| increased by excessive alcohol intake. However, | | | | body’s metabolism in generating energy |
| toxicity only occurs with vitamin A already | | | | from blood glucose, and are also created through |
| formed such as that obtained from liver. | | | | exposure to pollutants such as cigarette smoke |
| There are several forms of vitamin A, including | | | | and traffic fumes. They are electron deficient, so |
| the retinoid form originating from animal sources | | | | when they are generated they grab an electron |
| and the carotenoid forms that have a vegetable | | | | from tissue close by which destroys the cells |
| origin. Carotenoids are converted to vitamin A in | | | | involved. This can lead not only to the appearance |
| the liver, but the higher the concentration of beta | | | | of premature aging as the skin cells are damaged |
| carotene in the body, the smaller the percentage | | | | but also to serious health problems such as |
| that is converted to vitamin A, so beta carotene | | | | atherosclerosis and some forms of cancer. |
| is a safer source of vitamin A than retinoids. It is | | | | Vitamin A helps to protect against these by |
| only the finished form of vitamin A that is toxic, | | | | destroying the free radicals before they can do |
| and beta carotene is therefore self-regulating in its | | | | damage. It also helps build up resistance against |
| production. | | | | infections by supporting the immune system. |
| This vitamin is stored in the body in the form of | | | | Beta carotene is converted to vitamin A either by |
| the alcohol (retinol) and of retinyl esters. Studies | | | | cleaving at the center of the molecule, or by |
| have indicated that as much as 95% if the stored | | | | breaking it down from one of the ends. This latter |
| vitamin is in the form of the ester. The liver is | | | | process is carried out in the small intestine, and |
| responsible for releasing vitamin A to the body as | | | | the resultant vitamin stored in the liver in the |
| it is required. One of its better known effects is | | | | ester form. Only a proportion of what you eat is |
| on vision, and the old wives tale that carrots help | | | | converted to retinol ester in this way, and the |
| you to see in the dark has an element of truth in | | | | more beta carotene you consume, the less is |
| it. | | | | converted, so you can never suffer from an |
| In order for it to aid vision, retinol is oxidized to | | | | overdose of beta carotene-derived vitamin A. It |
| the aldehyde, retinal, that forms a complex with a | | | | might turn you yellow, but you won’t |
| molecule of opsin, a light sensitive protein found in | | | | suffer from excess vitamin A since the excess |
| the retina. Rhodopsin, as the complex is called, is | | | | beta carotene is stored in your body fat, including |
| an essential component of the biochemical chain | | | | the subcutaneous fat reserves. |
| of events that lead to the perception of light. It is | | | | Alpha carotene can also be used in the synthesis |
| extremely sensitive, and enables you see in very | | | | of vitamin A, but not as actively as beta |
| low levels of light. In other words it is essential for | | | | carotene. The best natural sources are fruits and |
| good night vision, so carrots do help you to see in | | | | vegetables, especially the red, yellow and orange |
| the dark! When a photon of light hits a molecule | | | | varieties such as carrots and apricots, and also |
| of rhodopsin, it leads eventually to an impulse | | | | the leafy green vegetables, although supplements |
| being sent up the optic nerve to the brain. | | | | are also a convenient way of maintaining your |
| One of its properties is its reaction to white light. | | | | beta carotene uptake. It is a much safer |
| When rhodopsin is exposed to white light it loses | | | | supplement than straight vitamin A for the |
| its pigmentation, and hence its photoreceptor | | | | reasons explained earlier. The supplement is not |
| properties and can take 30 minutes to | | | | useful just for its antioxidant effect, but also for |
| regenerate. That is why you lose your night sight | | | | its ability to protect you from excessive |
| if your retina is exposed to bright light. The more | | | | exposure to the sun. While not as effective as a |
| rhodopsin you can generate the quicker you | | | | good sun blocker, beta carotene does provide |
| develop night sight. | | | | some protection. |
| The other biochemical processes of the vitamin | | | | There is no doubt that beta carotene is a safer |
| include the synthesis of some glycoproteins and | | | | way to maintain an adequate vitamin A uptake |
| maintenance of normal bone density. Without | | | | due to the fact that you cannot take an |
| vitamin A, calcium is not properly absorbed by the | | | | overdose, since an overdose of beta carotene |
| body and glycoproteins are involved in this | | | | does not translate into the same dose of vitamin |
| process. A deficiency of vitamin A can lead to the | | | | A, and the change is self-regulating. It is therefore |
| abnormal development of bone and other health | | | | safer to obtain your vitamin A needs from |
| problems, so there are limits between the levels | | | | colored fruits and vegetables or beta carotene |
| of vitamin A in the body that must be maintained: | | | | supplements than from eating liver, from which |
| above or below these limits will lead to health | | | | the retinol is in a form that can cause damage in |
| problems, some of which can be extremely | | | | the event of consuming an excess. |
| serious. | | | | The old adage that you should never eat polar |
| Most of the biochemistry of vitamin A in the liver | | | | bear livers is a true one, and certainly has a |
| is initiated by the presence of alcohol, and | | | | provable scientific basis, so use beta carotene as |
| otherwise it is though to passively store the | | | | your main vitamin A source for maximum health |
| vitamin until needed when it is released into the | | | | benefits in the safest possible way. |
| blood. There are several ways in which the | | | | |