Editing Altitude (section)

==Effects on organisms==

===Humans===
{{main|Effects of high altitude on humans}}

Medicine recognizes that altitudes above {{convert|1500|m|ft}} start to affect humans,<ref>{{cite web|title=Non-Physician Altitude Tutorial |publisher=International Society for Mountain Medicine |url=http://www.ismmed.org/np_altitude_tutorial.htm |access-date=22 December 2005 |archive-url=https://web.archive.org/web/20051223065508/http://www.ismmed.org/np_altitude_tutorial.htm |archive-date=23 December 2005  }}</ref> and there is no record of humans living at extreme altitudes above {{convert|5500|-|6000|m|ft}} for more than two years.<ref name=highestHabitation>{{cite journal|last=West|first=JB|pmid=12631426|title=Highest permanent human habitation|journal=High Altitude Medical Biology|volume=3|pages=401–407|year=2002|doi=10.1089/15270290260512882|issue=4}}</ref> As the altitude increases, atmospheric pressure decreases, which affects humans by reducing the [[partial pressure]] of [[oxygen]].<ref name=pubmed>{{cite journal|title=Oxygen at high altitude|journal=British Medical Journal|first=Andrew J|last=Peacock|date=17 October 1998|volume=317|pages=1063–1066|pmid=9774298|issue=7165|pmc=1114067|doi=10.1136/bmj.317.7165.1063}}</ref> The lack of oxygen above {{convert|8000|ft|m|order=flip}} can cause serious illnesses such as [[altitude sickness]], [[high altitude pulmonary edema]], and [[high altitude cerebral edema]].<ref name=MedicalProblems>{{cite journal|last1=Cymerman|first1=A|last2=Rock|first2=PB|title=Medical Problems in High Mountain Environments. A Handbook for Medical Officers|publisher=U.S. Army Research Inst. of Environmental Medicine Thermal and Mountain Medicine Division Technical Report|volume=USARIEM-TN94-2|url=http://archive.rubicon-foundation.org/7976|year=1994|access-date=5 March 2009|archive-date=23 April 2009|archive-url=https://web.archive.org/web/20090423042510/http://archive.rubicon-foundation.org/7976|url-status=usurped}}</ref> The higher the altitude, the more likely are serious effects.<ref name=MedicalProblems/> The human body can [[altitude acclimatization|adapt to high altitude]] by breathing faster, having a higher heart rate, and adjusting its blood chemistry.<ref name=BordenHuman>{{cite book |last1=Young|first1=Andrew J.|last2=Reeves|first2=John T. |title=Human Adaptation to High Terrestrial Altitude. In: Medical Aspects of Harsh Environments |volume=2 |chapter=21 |location=Borden Institute, Washington, DC |year=2002 |chapter-url=http://www.bordeninstitute.army.mil/published_volumes/harshEnv2/harshEnv2.html| archive-url= https://web.archive.org/web/20090111214536/http://www.bordeninstitute.army.mil/published_volumes/harshEnv2/harshEnv2.html| archive-date= 11 January 2009 | url-status= live}}</ref><ref name=Acclimatization>{{cite journal |last1=Muza|first1=SR|last2=Fulco|first2=CS|last3=Cymerman|first3=A |title=Altitude Acclimatization Guide |journal=U.S. Army Research Inst. Of Environmental Medicine Thermal and Mountain Medicine Division Technical Report |issue=USARIEM–TN–04–05 |year=2004 |url=http://archive.rubicon-foundation.org/7616 |archive-url=https://web.archive.org/web/20090423042451/http://archive.rubicon-foundation.org/7616 |url-status=usurped |archive-date=23 April 2009 |access-date=5 March 2009 }}</ref> It can take days or weeks to adapt to high altitude. However, above {{convert|8000|m|ft|-3}}, (in the "[[death zone]]"), altitude acclimatization becomes impossible.<ref name="PBS">{{cite web|url= https://www.pbs.org/wgbh/nova/transcripts/2506everest.html|title= Everest:The Death Zone|work= Nova|publisher= PBS|date= 24 February 1998}}</ref>

There is a significantly lower overall mortality rate for permanent residents at higher altitudes.<ref>{{cite journal|last=West|first=John B.|title=Exciting Times in the Study of Permanent Residents of High Altitude|journal=High Altitude Medicine & Biology|date=January 2011|volume=12|issue=1|page=1|doi=10.1089/ham.2011.12101|pmid=21452955}}</ref> Additionally, there is a dose response relationship between increasing elevation and decreasing obesity prevalence in the United States.<ref name=Voss>{{cite journal|last1=Voss|first1=JD|last2=Masuoka|first2=P|last3=Webber|first3=BJ|last4=Scher|first4=AI|last5= Atkinson|first5=RL|title=Association of Elevation, Urbanization and Ambient Temperature with Obesity Prevalence in the United States|journal=International Journal of Obesity|year=2013|pmid=23357956|doi=10.1038/ijo.2013.5|volume=37|issue=10|pages=1407–1412|doi-access=free}}</ref> In addition, the recent hypothesis suggests that high altitude could be protective against Alzheimer's disease via action of erythropoietin, a hormone released by kidney in response to hypoxia.<ref>{{cite journal|last=Ismailov|first=RM|title=Erythropoietin and epidemiology of Alzheimer disease|journal=Alzheimer Dis. Assoc. Disord.|date=Jul–Sep 2013|volume=27|issue=3|pages=204–6|doi=10.1097/WAD.0b013e31827b61b8|pmid=23314061|s2cid=32245379}}</ref>
However, people living at higher elevations have a statistically significant higher rate of suicide.<ref name=Brenner>{{cite journal|last1=Brenner|first1=Barry|last2=Cheng|first2=David|last3=Clark|first3=Sunday|last4=Camargo|first4=Carlos A. Jr|title=Positive Association between Altitude and Suicide in 2584 U.S. Counties|journal=High Altitude Medicine & Biology|date=Spring 2011|volume=12|issue=1|pages=31–5|pmid=21214344|doi=10.1089/ham.2010.1058|pmc=3114154}}</ref> The cause for the increased suicide risk is unknown so far.<ref name=Brenner/>

====Athletes====
For athletes, high altitude produces two contradictory effects on performance. For explosive events (sprints up to 400 metres, [[long jump]], [[triple jump]]) the reduction in atmospheric pressure signifies less atmospheric resistance, which generally results in improved athletic performance.<ref>{{cite journal|last1=Ward-Smith|year=1983|title=The influence of aerodynamic and biomechanical factors on long jump performance|journal=Journal of Biomechanics|volume=16|pages=655–658|doi=10.1016/0021-9290(83)90116-1|pmid=6643537|first1=AJ|issue=8}}</ref> For endurance events (races of 5,000 metres or more) the predominant effect is the reduction in oxygen which generally reduces the athlete's performance at high altitude. Sports organizations acknowledge the effects of altitude on performance: the International Association of Athletic Federations (IAAF), for example, marks record performances achieved at an altitude greater than {{convert|1000|m|ft}} with the letter "A".<ref>{{cite web |url=http://www.iaaf.net/mm/Document/06/32/50/63250_PDF_English.pdf |archive-url=https://web.archive.org/web/20131022135302/http://www.iaaf.net/mm/Document/06/32/50/63250_PDF_English.pdf |archive-date=22 October 2013 |title=IAAF World Indoor Lists 2012 |date=9 March 2012 |url-status=usurped |publisher=IAAF Statistics Office   }}</ref>

Athletes also can take advantage of altitude acclimatization to increase their performance. The same changes that help the body cope with high altitude increase performance back at sea level.<ref name="pmid16497842">{{cite journal |last1=Wehrlin|first1=JP|last2=Zuest|first2=P|last3=Hallén|first3=J|last4=Marti|first4=B |title=Live high—train low for 24 days increases hemoglobin mass and red cell volume in elite endurance athletes |journal=J. Appl. Physiol. |volume=100 |issue=6 |pages=1938–45 |date=June 2006 |pmid=16497842 |doi=10.1152/japplphysiol.01284.2005 }}</ref><ref name="pmid17805094">{{cite journal |last1=Gore|first1=CJ|last2=Clark|first2=SA|last3=Saunders|first3=PU |title=Nonhematological mechanisms of improved sea-level performance after hypoxic exposure |journal=Med Sci Sports Exerc |volume=39 |issue=9 |pages=1600–9 |date=September 2007 |pmid=17805094 |doi=10.1249/mss.0b013e3180de49d3 |doi-access=free }}</ref> These changes are the basis of [[altitude training]] which forms an integral part of the training of athletes in a number of endurance sports including track and field, distance running, triathlon, cycling and swimming.

===Other organisms===
{{main|Organisms at high altitude}}
Decreased oxygen availability and decreased temperature make life at high altitude challenging. Despite these environmental conditions, many species have been successfully [[high-altitude adaptation|adapted at high altitudes]]. Animals have developed physiological adaptations to enhance oxygen uptake and delivery to tissues which can be used to sustain metabolism. The strategies used by animals to adapt to high altitude depend on their [[Morphology (biology)|morphology]] and [[phylogeny]]. For example, small mammals face the challenge of maintaining body heat in cold temperatures, due to their small volume to surface area ratio. As oxygen is used as a source of metabolic heat production, the hypobaric hypoxia at high altitudes is problematic.

There is also a general trend of smaller body sizes and lower [[species richness]] at high altitudes, likely due to lower oxygen partial pressures.<ref name=macroinvertrichness>{{cite journal|last=Jacobsen|first=Dean|title=Low oxygen pressure as a driving factor for the altitudinal decline in taxon richness of stream macroinvertebrates|journal=Oecologia|volume=154|pages=795–807|doi=10.1007/s00442-007-0877-x|issue=4|pmid=17960424|date=24 September 2007|bibcode=2008Oecol.154..795J|s2cid=484645}}</ref> These factors may decrease [[Productivity (ecology)|productivity]] in high altitude habitats, meaning there will be less energy available for consumption, growth, and activity.<ref name="trout">{{cite journal|last1=Rasmussen|first1=Joseph B.|first2=Michael D.|last2=Robinson|first3=Alice|last3=Hontela|first4=Daniel D.|last4=Heath|title=Metabolic traits of westslope cutthroat trout, introduced rainbow trout and their hybrids in an ecotonal hybrid zone along an elevation gradient|journal=Biological Journal of the Linnean Society|volume=105|pages=56–72|doi=10.1111/j.1095-8312.2011.01768.x|date=8 July 2011|doi-access=free}}</ref>

However, some species, such as birds, thrive at high altitude.<ref>{{cite journal|last1=McCracken|first1=K. G.|last2=Barger|first2=CP|last3=Bulgarella|first3=M|last4=Johnson|first4=KP|last5=Sonsthagen|first5=SA|last6=Trucco|first6=J|last7=Valqui|first7=TH|last8=Wilson|first8=RE|last9=Winker|first9=K|display-authors=4|title=Parallel evolution in the major haemoglobin genes of eight species of Andean waterfowl|journal=Molecular Evolution|date=October 2009|volume=18|issue=19|pages=3992–4005|doi=10.1111/j.1365-294X.2009.04352.x|pmid=19754505|last10=Sorenson|first10=M. D.|bibcode=2009MolEc..18.3992M |s2cid=16820157}}</ref> Birds thrive because of physiological features that are advantageous for high-altitude flight.