All of the vitamins are used as specific treatments for their respective deficiency diseases. The dosages re-quired will vary depending on the severity of the dis-ease and the vitamin. Vitamins have also been used like drugs to “treat” diseases. However, unlike drug prod-ucts, vitamins are not reviewed by the U. S. Food and Drug Administration before formulations appear on the market. Vitamins are considered to be dietary sup-plements under the Dietary Supplement Health and Education Act (DSHEA). Vitamins and other dietary supplements are not permitted to be marketed as a treatment or cure for a specific disease or condition un-less the vitamin is approved as a drug for that purpose. However, under DSHEA, supplement manufacturers may make health claims, such as the link between a food substance and a disease or health-related condition. This may make it difficult for patients to assess the need for vitamin supplementation.
Legitimate clinical research is being conducted with vitamins in many areas including heart disease, ophthal-mological disease, neurocognitive function, and derma-tological diseases. It is important for physicians to be aware of scientific information that either supports or refutes a role for vitamins in the maintenance of health or in the avoidance of disease.
Vitamin A can suppress many chemically induced tu-mors in the laboratory. Epidemiological evidence sug-gests that foods rich in carotenes or vitamin A are asso-ciated with a lower risk of cancer. However, the use of vitamin A supplementation is not advised because of the toxicities produced by large amounts of this vitamin.
The antioxidant properties of vitamins C and E can inhibit the formation of some carcinogens. The antioxi-dant vitamins have been studied as cancer chemopre-ventive agents for many cancer types, including gas-trointestinal and ovarian cancers. However, data are not sufficient to draw conclusions about the vitamins’ ef-fects on human cancers.
The role of the antioxidant properties of vitamins C, E, and β-carotene in the prevention of cardiovascular dis-ease has been the focus of several recent studies. Antioxidants reduce the oxidation of low-density lipoproteins, which may play a role in the prevention of atherosclerosis. However, an inverse relationship be-tween the intake or plasma levels of these vitamins and the incidence of coronary heart disease has been found in only a few epidemiological studies. One study showed that antioxidants lowered the level of high-density lipoprotein 2 and interfered with the effects of lipid-altering therapies given at the same time. While many groups recommend a varied diet rich in fruits and veg-etables for the prevention of coronary artery disease, empirical data do not exist to recommend antioxidant supplementation for the prevention of coronary disease.
Niacin has been used clinically to lower serum cho-lesterol levels . It is used as adjunctive therapy in patients with hyperlipidemia. It is one of the drugs of first choice for patients who do not respond ad-equately to diet and weight loss.
Vitamin A and its retinoid analogues have gained pop-ularity in the treatment of acne and other dermatologi-cal diseases .
Vitamin K supplements are given to neonates until normal intestinal bacteria that are capable of producing the vitamin develop.
Folic acid supplements are given to pregnant women to decrease the risk of neural tube defects such as spina bifida. Prenatal vitamin preparations that contain higher concentrations of folic acid must be dispensed under a health care worker’s guidance because high folate in-takes can mask the symptoms of pernicious anemia.
A study of the vitamins in neurocognitive diseases such as Alzheimer’s disease have not provided sufficient evidence to demonstrate that vitamins play a role in the prevention of these diseases.
Clinical trials have also been conducted to study the effect of the antioxidants on the progression of age-related macular degeneration (AMD) and vision loss. The Age-Related Eye Disease Study Research Group recommends supplements of zinc and antioxidants for adults at risk for developing AMD. However, the group cautions about unknown long-term effects of high-dose supplementation.
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