Nutritional Needs in Cold and High-Altitude Environments Applications for Military Personnel in Field Operations (1996) / Chapter Skim
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21 Oxidative Stress at High Altitudes and Effects of Vitamin E
21 Oxidative Stress at High Altitudes and Effects of Vitamin E
Pages 393-418
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From page 393... ...
A shift to the prooxidative state is called oxidative stress (Sies, 1993~. The antioxidative "strategy" of aerobic cells is targeted at inhibiting or blocking potentially toxic oxygen species or their ' I
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From page 394... ...
There is growing evidence that oxidative injury mediated by tree radicals is an important factor in various pathologies, including adverse metabolic reactions at high altitudes. Table 21-1 summarizes the many intra- and extracellular sources of free radicals.
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From page 395... ...
The main objective, even in the case of intense physical performance, is always to maintain the integrity of the membrane structures or at least to ensure that changes are reversible (Berg et al., 1987~. The major cause of membrane damage is the formation of free radicals that can arise from various processes during metabolism.
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From page 396... ...
tH ~LOO.~ c: ASH ~ r~ al 10. LOON ~ O2 Rqx~b,-' FIGURE 21-1 Scheme for lipid peroxidation chain reactions initiated by free radicals.
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From page 397... ...
weight molecules. which in tune induce rnclin.~1 chain THE DEFENSE SYSTEM As mentioned above, the antioxidative strategy of aerobic cells is targeted at inhibiting or blocking potentially toxic oxygen species or their derivatives at the various levels of formation or blocking their reaction with biomolecules (Elstner, 1990~.
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From page 398... ...
For example, it has been shown to scavenge effectively superoxide anions, hydrogen peroxide, the hydroxyl (OH ~ radical, aqueous peroxyl radicals, as well as singlet oxygen (Stocker and Fret, 1991~. As an antioxidant, vitamin C undergoes a two-electron oxidation to dehydroascorbic acid with the intermediate formation of a relatively unreactive ascorbyl radical (Bielski and Richter, 1975~.
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From page 399... ...
EVIDENCE FOR INCREASED OXIDATIVE STRESS AT HIGH ALTITUDES With respect to life, the main characteristics of high altitude are the decreased availability of oxygen, with its influence on metabolism and thereby on physical and mental performance, as well as increased ultraviolet radiation, wide temperature differences, sometimes increased psychological stress, dehydration, and insufficient nutrient intake. High-Altitude Hypoxia Aerobic energy supply is necessary for all higher life forms.
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From page 400... ...
In animals, exercise-induced lipid peroxidation was prevented by vitamin E administration (Dillard et al., 1977; Packer, 1984~. To test if there is indeed an increased oxidative stress leading to increased lipid peroxidation at high altitudes, the amount of exhaled pentane was determined by gas chromatography (Simon-Schnass and Pabst, 1988~.
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From page 401... ...
, however, permits the conclusion that the oxidative stress led to depletion of vitamin E and/or other antioxidative substances. To prove that the reason for this depletion was indeed the effect of an increased free radical production, the test was repeated during the above described expedition to Solo Khumbu (Simon-Schnass, 1994~.
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From page 402... ...
FIGURE 21-3 Filterability of red blood cells (without dimension) from subjects of two different expeditions to high altitudes.
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From page 403... ...
Given the results of the pentane measurement, these results show that there is increased oxidative stress at high altitudes and that supplementation with vitamin E, an antioxidant, can counteract its negative consequences. Increased Ultraviolet Radiation with Increasing Altitude The skin is exposed to radiation of a wavelength between about 300 and 3,000 nm, including inhered, visible light, and ultraviolet (UV)
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From page 404... ...
This amount is within the order of the intramolecular binding energy, which is the reason why singlet and triplet forms as well as free radicals can be produced (Kindl and Raab, 19934. The increased UV-B radiation at high altitudes may thus be an important reason for increased oxidative stress at high altitudes.
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From page 405... ...
Oral 3-carotene administration significantly increased the minimal erythema dose of solar radiation in humans (Mathews-Roth et al., 19729. This result may be caused by the photoprotective mechanism of 3-carotene, a potent singlet oxygen scavenger at low partial pressure of oxygen (Mathews-Roth et al., 1972~.
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From page 406... ...
Little research has been performed on the effect of altitude on anaerobic threshold. Results of the placebo group in the above described study, however, confirm the previous observation that a prolonged stay at high altitudes leads to reduced physical performance, reflected in a decreased anaerobic threshold.
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From page 407... ...
There is increased formation of free radicals, which triggers lipid peroxidation. As a result, membrane fluidity (measured by erythrocyte filterability)
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From page 408... ...
In this chapter, only the data on white blood cells and two antiaggregational substances are discussed. The viscosity of blood is mainly determined by the amount of blood cells, their flexibility, and the plasma viscosity.
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From page 409... ...
As shown in Figure 21-6 a marked increase in white blood cells was shown in the control group, whereas no change occurred in the supplemented group. On.the basis of data in the literature, an increased granulocyte stimulation can be assumed to occur in such a situation.
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From page 410... ...
Many of these reactions produce or are influenced by free radicals. Supplementation with antioxidants seems to stabilize both leukocytes and the endothelial cells and to protect against splitting of proteins.
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From page 411... ...
Until now no data have been collected concerning the increased production of free radicals in hot environments. However, it has been suggested that work in hot environments could create a hypoxic condition in muscle due to the redistribution of blood from the muscle to the skin (Young, 1990~.
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From page 412... ...
Because the melting of 1 liter of water from snow takes about 1 hour under these conditions, it is not surprising that hi~,h-altitude climbers generally do not meet their fluid demand and return to base camp more or less dehydrated (Personal communications with exper~ienced climbers during the various expeditions, 1986, 1988, 1990~. In this case, the fluid deficit can be compensated for by water only, but in practice it is usually by tea (Personal communications with experienced climbers during the various expeditions, 1986, 1988, 1990~.
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From page 413... ...
The second expedition was a scientific project in the Solo Khumbu for which the food supply was organized by experienced mountaineers. In the first case, data were obtained by weighing the food consumed by the group over the entire period and then calculating the average intake by dividing this amount per person and day at the base camp.
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From page 414... ...
The most important causes of free radical formation are the respiratory chain itself, hypoxia, and increased ultraviolet radiation. Whether high ardor low temperatures and dehydration lead to an increased formation of free radicals is not clear at the present time.
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From page 415... ...
Savin, E.E Dumelin, and A.L. Tappel 1978 Effects of exercise, vitamin E, and ozone on pulmonary function and lipid peroxidation.
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From page 416... ...
Packer 1989 Free radical reduction mechanism in mouse epidermis skin homogenates.
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From page 417... ...
Slater, and R.L. Wilson 1979 Direct observation of a free radical interaction between vitamin E and vitamin C
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From page 418... ...
Volger, E 1984 Einflusse der hypoxie auf die erythropoese, sauerstoffbindung des hemoglobins, gerinnung und rheologie des brutes.
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