| Popis: |
Vitamin E was discovered over 75 years ago, yet it has been only recently recognized that human vitamin E deficiency occurs as a result of fat malabsorption syndromes, defects in lipoprotein metabolism, and defects in the gene for the *-tocopherol transfer protein. Although the frequency of human vitamin E deficiency is unknown, it is likely that it is very rare. In individuals at risk, it is clear that vitamin E supplements should be recommended to prevent deficiency symptoms. What about their use in normal individuals? Vitamin E supplementation in normal individuals is quite controversial. It has been assumed that usual dietary vitamin E intakes are adequate because human vitamin E deficiency is rare and experimental vitamin E deficiency difficult to produce in laboratory animals. A continuing problem in nutrition is whether nutrients have beneficial effects when consumed in amounts in excess of those 'required' by the body. For most vitamins, excess amounts are wasted and provide no added benefits. Indeed, some fat soluble vitamins can be stored and excess amounts become toxic. Antioxidant nutrients may, however, be different. Heart disease and stroke, cancer, chronic inflammation, impaired immune function, Alzheimer's disease: a case can be made for the role of oxygen-free radicals in the etiology of all of these disorders and even in aging itself. Do antioxidant nutrients counteract the effects of free radicals and thereby ameliorate these disorders? And if so, do large antioxidant supplements have beneficial effects beyond 'required' amounts or even in amounts beyond those that could be obtained from a well-balanced diet? These are questions for which not only scientists, but also the public, are eagerly awaiting the answers. |
