Many people seek recreation and adventure at high altitudes. Skiing and snowboarding are sports that require at least short-term exposure to altitudes above 2500 m; trekking and mountain climbing, although still for the particularly stalwart, are drawing more and more adventurers every year to base camps as high as 5000 m or 6000 m. Ascent to high altitude results in acute and long-term physiologic changes that have the potential to profoundly affect nutrient requirements for the traveler and adventurer. Immediately upon arrival at high altitude, because of the decrease in inspired oxygen (O₂) pressure, alveolar and arterial O₂ pressures decrease, and maximal O₂ consumption (VO_2MAX) decreases.<sup>10Braun B, Mawson JT, Muza S, et al: Women at altitude: Blood glucose utilization at 4300 m compared with sea level during exercise at the same absolute and relative intensity. J Appl Physiol, submitted

Cliquez ici pour aller à la section Références, 12Brooks G.A., Butterfield G.E., Wolfe R.R., et al. Increased dependence on blood glucose after acclimatization to 4300m J Appl Physiol 1991 ;  70 : 919-927

Cliquez ici pour aller à la section Références, 33Fulco C.S., Rock P.B., Cymerman A. Maximal and submaximal exercise performance at altitude Aviat Space Environ Med 1998 ;  69 : 793-801

Cliquez ici pour aller à la section Références, 70Roberts A.C., Reeves J.T., Butterfield G.E., et al. Altitude and beta-blockade augment glucose utilization during submaximal exercise J Appl Physiol 1996 ;  80 : 605-615

Cliquez ici pour aller à la section Références, 86Young A.J., Young P.M. Human acclimatization to high terrestrial altitude Human Performance Physiology and Environmental Medicine at Terrestrial Extremes Indianapolis, IN: Benchmark Press (1988).  497-543

Cliquez ici pour aller à la section Références</sup> Submaximal work performance is also dramatically reduced.<sup>2Askew E.W. Nutrition and performance in hot, cold, and high altitude environments Nutrition in Exercise and Sport Boca Raton, FL: CRC Press (1998).  597-619

Cliquez ici pour aller à la section Références, 70Roberts A.C., Reeves J.T., Butterfield G.E., et al. Altitude and beta-blockade augment glucose utilization during submaximal exercise J Appl Physiol 1996 ;  80 : 605-615

Cliquez ici pour aller à la section Références, 86Young A.J., Young P.M. Human acclimatization to high terrestrial altitude Human Performance Physiology and Environmental Medicine at Terrestrial Extremes Indianapolis, IN: Benchmark Press (1988).  497-543

Cliquez ici pour aller à la section Références</sup> Some individuals experience symptoms, including headache, nausea, vomiting, insomnia, lassitude, and malaise<sup>40Hackett P.H., Rennie D., Grover R.F., et al. Acute mountain sickness and the edema of high altitude Respir Physiol 1981 ;  46 : 383-390 [cross-ref]

Cliquez ici pour aller à la section Références</sup> known as acute mountain sickness (AMS), a condition that also often results in severe anorexia.

Over the first few days of high-altitude exposure, AMS subsides, and a cluster of physiologic adaptations occur that restore, at least partially, O₂ homeostasis. The low arterial O₂ pressure stimulates chemoreceptors in the heart and respiratory centers of the brain to increase heart and breathing rates. This adaptation increases the acquisition and delivery of O₂ to tissues<sup>24Cymerman A. The Physiology of High-Altitude Exposure Nutritional Needs in Cold and in High-Altitude Environments Washington, DC: National Academy Press (1996). 

Cliquez ici pour aller à la section Références, 59Muza S.R., Jackson R., Rock P.B., et al. Effects of high terrestrial altitude on work performance in an NBC protective uniform USARIEM Technical Report 1997 ; T97-T97AD A328002.

Cliquez ici pour aller à la section Références</sup> and is, in part, responsible for an increase in basal energy expenditure at high altitude. The increase in respiratory rate decreases arterial carbon dioxide content, creating an alkalosis and limiting respiratory stimulation.<sup>24Cymerman A. The Physiology of High-Altitude Exposure Nutritional Needs in Cold and in High-Altitude Environments Washington, DC: National Academy Press (1996). 

Cliquez ici pour aller à la section Références</sup> The kidney responds to the alkalosis by increasing the excretion of bicarbonate, with an associated diuresis and decrease in plasma volume. The resultant hemoconcentration helps to normalize arterial O₂ content.<sup>36Grover R.F., Reeves J.T., Maher J.T., et al. Maintained stroke volume but impaired arterial oxygenation in man at high altitude with supplemental CO₂ Circ Res 1976 ;  38 : 391-396

Cliquez ici pour aller à la section Références, 37Grover R.F., Weil J.V., Reeves J.T. Cardiovascular adaptation to exercise at high altitude Exercise and Sport Science Reviews New York: Macmillian (1986).  269-302

Cliquez ici pour aller à la section Références, 51Krzywicki H.J., Consolazio C.F., Johnson H.L., et al. Water metabolism in humans during acute high altitude exposure (4,300 m) J Appl Physiol 1971 ;  30 : 806-809

Cliquez ici pour aller à la section Références, 86Young A.J., Young P.M. Human acclimatization to high terrestrial altitude Human Performance Physiology and Environmental Medicine at Terrestrial Extremes Indianapolis, IN: Benchmark Press (1988).  497-543

Cliquez ici pour aller à la section Références</sup> With additional time at high altitude, the O₂-carrying capacity of the blood is further expanded by the secretion of erythropoeitin (EPO),<sup>37Grover R.F., Weil J.V., Reeves J.T. Cardiovascular adaptation to exercise at high altitude Exercise and Sport Science Reviews New York: Macmillian (1986).  269-302

Cliquez ici pour aller à la section Références, 38Grover R.F., Selland M.A., McCullough R.G., et al. Beta-adrenergic blockade does not prevent polycythemia or decrease in plasma volume in men at 4300 m altitude Eur J Appl Physiol 1998 ;  77 : 264-270 [cross-ref]

Cliquez ici pour aller à la section Références, 65Reeves J.T., McCullough R.T., Moore L.G., et al. Sea-level P co₂ relates to ventilatory acclimatization at 4300 m J Appl Physiol 1993 ;  75 : 1117-1122

Cliquez ici pour aller à la section Références</sup> which stimulates red blood cell production in, and release of reticulocytes from, bone marrow and thereby potentially increases red cell mass and O₂-carrying capacity. The ability to perform maximal exercise (VO_2MAX) remains depressed in comparison to at sea level,<sup>10Braun B, Mawson JT, Muza S, et al: Women at altitude: Blood glucose utilization at 4300 m compared with sea level during exercise at the same absolute and relative intensity. J Appl Physiol, submitted

Cliquez ici pour aller à la section Références, 12Brooks G.A., Butterfield G.E., Wolfe R.R., et al. Increased dependence on blood glucose after acclimatization to 4300m J Appl Physiol 1991 ;  70 : 919-927

Cliquez ici pour aller à la section Références, 24Cymerman A. The Physiology of High-Altitude Exposure Nutritional Needs in Cold and in High-Altitude Environments Washington, DC: National Academy Press (1996). 

Cliquez ici pour aller à la section Références, 36Grover R.F., Reeves J.T., Maher J.T., et al. Maintained stroke volume but impaired arterial oxygenation in man at high altitude with supplemental CO₂ Circ Res 1976 ;  38 : 391-396

Cliquez ici pour aller à la section Références, 37Grover R.F., Weil J.V., Reeves J.T. Cardiovascular adaptation to exercise at high altitude Exercise and Sport Science Reviews New York: Macmillian (1986).  269-302

Cliquez ici pour aller à la section Références, 59Muza S.R., Jackson R., Rock P.B., et al. Effects of high terrestrial altitude on work performance in an NBC protective uniform USARIEM Technical Report 1997 ; T97-T97AD A328002.

Cliquez ici pour aller à la section Références, 86Young A.J., Young P.M. Human acclimatization to high terrestrial altitude Human Performance Physiology and Environmental Medicine at Terrestrial Extremes Indianapolis, IN: Benchmark Press (1988).  497-543

Cliquez ici pour aller à la section Références</sup> but performance of submaximal work improves<sup>52Maher J.T., Jones L.G., Hartley L.H. Effects of high-altitude exposure on submaximal endurance capacity of men J Appl Physiol 1974 ;  37 : 895-898

Cliquez ici pour aller à la section Références, 86Young A.J., Young P.M. Human acclimatization to high terrestrial altitude Human Performance Physiology and Environmental Medicine at Terrestrial Extremes Indianapolis, IN: Benchmark Press (1988).  497-543

Cliquez ici pour aller à la section Références</sup> relative to immediate high-altitude exposure.

With prolonged exposure to high altitude, anorexia may or may not subside, and basal energy requirements may or may not remain elevated. The most consistent finding in studies of prolonged exposure of visitors to high altitude is weight loss.^{*References 7,8,14,20,23,26,34,39,43,45,46,48,49,50,51,63,68,69,72,73,75,79,84 and 85} The primary cause of this weight loss is thought to be the energy imbalance created by the opposing phenomena of inadequate energy intake and elevated energy expenditure.<sup>14References 7,8,14,20,23,26,34,39,43,45,46,48,49,50,51,63,68,69,72,73,75,79,84 and 85

Cliquez ici pour aller à la section Références, 15References 7,8,14,20,23,26,34,39,43,45,46,48,49,50,51,63,68,69,72,73,75,79,84 and 85

Cliquez ici pour aller à la section Références, 47References 7,8,14,20,23,26,34,39,43,45,46,48,49,50,51,63,68,69,72,73,75,79,84 and 85

Cliquez ici pour aller à la section Références</sup>

This series of physiologic responses to high altitude suggests an increase in the need for some nutrients at high altitudes compared with that at sea level. This article discusses the evidence for these increased requirements and makes recommendations regarding appropriate intakes at high altitude. Nutrients to be discussed include energy and the food components that supply it (i.e., protein, carbohydrate, and fat), water, vitamins (especially vitamin E), and minerals (especially iron).