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Can antioxidants be taken for longer periods?

Q: Can antioxidants be continued for long periods? We know that vitamin A and Beta carotene have accumulative properties and can lead to hypervitaminosis. But most of the doctors prescribe antioxidants for prolonged periods. Can calcium preparations be continued for longer period? Most of them contain Vitamin D, which also has an accumulative property. Please advise.

A:Antioxidants are substances whose presence in relatively low concentration significantly neutralizes dangerous compounds known as free radicals (molecules with an unpaired electron) which are normally produced during cellular metabolism. These free radicals are unstable and can produce cellular damage such as lipid peroxidation (damage of lipid membranes) and changes in membrane protein structure - both of which have been suggested as possible causes in the development of heart disease and cancer. Antioxidants inhibit the rate of this oxidation and neutralise free radicals before they interact with living tissue, detoxifying them into water and oxygen. They may be either natural/physiological being normally present in the body or pharmacological/synthetic. Antioxidants action may be a) enzymatic (catalase, super oxide dismutase) that breakdown free radicals, b) preventive (ceruloplasmin, lactoferrin, transferrin) that bind to metallic ions or c) scavengers (vitamin C, beta carotene, flavonoids, tocopherol) that break the chains in free radicals. Epidemiological observations reveal lower cancer rates in people whose diets are rich in fruits and vegetables leading to the theory that these diets contain substances, possibly antioxidants, which protect against the development of cancer. Antioxidants are also thought to have a role in slowing the aging process and preventing heart disease and strokes, but the data is still inconclusive. Their role in transplantation, diabetes, inflammatory disease, hypertension, AIDS, etc. is currently being intensely researched into this topic but till date none of the large, well-designed studies have shown that dietary supplementation with extra antioxidants reduces the risk of developing cancer. In fact one study showed an increased risk of lung cancer in male smokers who took antioxidants as against smokers who did not. This raises the issue that antioxidants may be harmful under certain conditions and as yet plenty of controversy remains as to the long-term health benefits. Although there is no evidence that they will harm in the usual doses, megadoses have been reported to have side effects. Therefore from a public health perspective it is premature to make recommendations regarding antioxidant supplements and disease prevention unless studies conclusively show this. Perhaps the best advice is to eat 5 servings of fruit & vegetables per day. Before initiating therapy it is imperative that the rationale for its use is clearly defined – if the disease is caused by oxidative damage, does an antioxidant defect exist, is the antioxidant concentration sufficient at the site of its intended action, its proper dose, duration and safety? Calcium is required by the body for proper bone formation and also for effective functioning of cardiac, musculo-skeletal and nervous systems. It is alos needed for blood clotting and is an important constituent of several enzymes. It is stored in the bones and is constantly exchanged with blood depending on the body's need for calcium. In states of low calcium levels in the blood, it is mobilised from the bones weakening them and leading to osteoporosis. Calcium supplements are needed for patients who are unable to get enough calcium in their diet or who need for more calcium. It is used to prevent or treat conditions causing hypocalcaemia (low calcium levels in blood). There is increased requirement in pregnancy, lactation, children, and adolescents. Post- menopausal women may need to take calcium supplements to help prevent osteoporosis. Calcium may be contraindicated in cardiac disease, hypercalcaemia, hypercalciuria, hyperparathyroidism, and sarcoidosis. Vitamin D enhances calcium uptake into the cells of the body when blood calcium levels are low. However, when blood calcium levels are high, levels of a particular metabolite of vitamin D (1:25-dihydroxyvitamin D) fall, and this in turn reduces the rate at which calcium is transferred into cells.

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