Sample Term Paper: The Effects of Altitude on Human Physiology

Research Paper Health
Apr 17, 2022

The ability of the human body to adapt to its environment is one of the key factors in its survival and evolution . This becomes a more significant trait in environments that are foreign to the body, such as the variations in altitude. In a typical human environment, the body utilizes enough oxygen to give cells power and allow the different organs to operate. The changes in altitude, however, can decrease or increase the volume of air which affects the intake of oxygen. This can lead to altitude sickness which has varying symptoms and effects on the human body. The effects of altitude on human physiology depend on the response of the body which can lead to a decline in bodily functions.

Levels of Altitude

The effects of altitude on human physiology vary depending on an individual’s current level of altitude. According to the Army Public Health Center, there are five levels of altitude, from low to extreme. Low altitudes, which are below 1,200 meters, do not have significant effects on the body. This altitude, which includes the sea level, is where most humans have adapted and lived. The moderate level is the second level and ranges from 1,200 to 2,400 meters. Individuals at this level can begin to feel the symptoms of acute altitude exposure as well as a decrease in physical performance. This level includes high mountains that hikers tend to visit, meaning that humans can safely travel to this altitude without the need for special equipment.

Next is the high altitude level which ranges from 2,400 to 4,000 meters and is when most individuals will feel acute altitude sickness. These altitudes are around the height of large mountains, such as Mount Bezymianny in  Kamchatka and Granite Peak in Montana. Going further from this level will lead to the “very high altitude” level which ranges from 4,000 to 5,500 meters. From this level, humans will suffer altitude sickness unless they have the proper gear for the environment. Lastly, the extreme altitude level is any altitude that is above 5,500 meters. Humans cannot function properly at this altitude and will require the aid of specialized gear to survive the extreme environment. Mount Everest, the highest peak on Earth, is around 8,800 meters- that is 3,000 meters above the minimum altitude for the extreme levels.

General Effects of Altitude Exposure

Altitude exposure will have varying effects depending on an individual’s health, the altitude level, and the preparation they practiced before their ascent. Simple symptoms, such as a headache and nausea, are clear signs of altitude sickness despite the absence of other symptoms. There are also other effects like decreased physical performance, psychological effects, dehydration, and malnutrition (Altitude Effects, 2018). Psychological effects can include personality changes and strange sensations regarding the senses. Effects like dehydration and malnutrition are due to the physical reactions of the body which can decrease and waste energy. 

Individuals, whether they are trained soldiers or regular civilians, can suffer from altitude sickness despite their physical conditions. Most of these symptoms are due to the fewer oxygen molecules that humans can inhale at high altitudes, weakening the performance of body parts (Scott, 2018). Soldiers that are physically fit cannot train their bodies to use less oxygen unless they undergo acclimatization. Without this process, the human body will struggle to adapt to the changes in oxygen intake which will result in the manifestation of symptoms. Some studies, however, indicate that certain genes can affect the rate at which individuals experience altitude sickness (Liu et al., 2018). It is also important to note that the general effects are present in common acute mountain sickness as well as in more fatal conditions like high altitude cerebral edema. 

Acute Mountain Sickness

Acute mountain sickness (AMS) is a common condition that individuals can experience when going into high altitude levels. This form of altitude sickness is less severe compared to high altitude edemas which can be fatal (Timothy et al., 2022). AMS results from the lack of sufficient oxygen going to the body which has a large effect on brain functions. It is less serious since the symptoms only involve headaches, nausea, lethargy, and disturbed sleep (Scott, 2018). Individuals will also have different experiences where some will suffer from AMS after a quick ascent while others can seem immune to its effects. 

AMS symptoms can occur between six to 48 hours after ascending to high altitude levels. As mentioned above, it will result in headaches, lethargy, and dizziness but can also include vomiting, and dizziness. According to Timothy et al. (2022), a simple headache after ascending to high altitudes can be a clear sign of AMS despite the lack of other symptoms. Depending on the altitude level, AMS can disappear without the need for treatment. Despite this, studies indicate that AMS is a predecessor for high altitude pulmonary edema and high altitude cerebral edema (Timothy et al., 2022). If an AMS patient does not take treatment for their symptoms, they may increase the chance of developing severe and lethal conditions.

High Altitude Pulmonary Edema

High altitude pulmonary edema or HAPE is a more severe altitude sickness that can result in fatality. An individual can suffer HAPE once they experience hypoxia, a significant lack of oxygen in the body. The chances of HAPE increase depending on the altitude. According to Jensen & Vincent. (2021b), HAPE can occur 0.6% to 6% more at an altitude of 4,500 meters and 2% to 15% more at 5,500 meters. Individuals may still suffer from HAPE when around 2,000 and 2,500 meters, however, the chances are low and they may instead get AMS. The chance of HAPE can also increase up to 60% if an individual previously experienced HAPE during a climb. This indicates that individuals with a history of HAPE should be aware of their symptoms to avoid suffering from severe complications.

Aside from hypoxia and a previous HAPE diagnosis, individuals can suffer from the illness because of rapid ascent, use of sleep medication, cold temperatures, and excessive physical performance in high altitudes (Derby, R. 2010; Gallagher, SA. and Hacket PH., 2004; Basnyat B. and Murdoch DR., 2003; cited in Jensen & Vincent, 2021b).  As mentioned above, genetics can also be a factor in the development of HAPE which individuals and physicians should take into account during diagnosis.

The symptoms of HAPE include fatigue, dyspnea, dry cough, rales, and cyanosis. The symptoms vary depending on the progression of the illness and the patient’s treatment. Since HAPE is a result of hypoxia, an individual may first experience AMS which can lead them to disregard symptoms. This can cause severe effects like rales, cyanosis, and even death. Untreated HAPE has a 50% mortality rate while a treated illness only has an 11% mortality rate. (Jensen & Vincent, 2021b). These statistics indicate that acknowledging the first symptoms of HAPE and getting treatment is necessary to avoid fatal outcomes.

High Altitude Cerebral Edema

High altitude cerebral edema or HACE is the most severe form of altitude sickness. Researchers agree that HACE is the end stage of AMS since most cases of illness include the diagnosis of both AMS and HAPE Jensen & Vincent, 2021a; Turner et al., 2021). While this is the case for a lot of diagnoses, the absence of AMS or HAPE is not an indicator of the absence of HACE (Jensen & Vincent, 2021a). A patient can still develop abnormal water accumulation in the brain without suffering from AMS of HAPE, which is the definition of cerebral edema.

Similar to the other illness, HACE occurs at a certain altitude, above 4,00 meters, but more aggressive forms can occur at lower altitudes. The symptoms include all the effects of AMS and HAPE along with ataxia, altered mental status, confusion, behavioral changes, papilledema, and organic brain syndrome (Turner et al., 2021). According to researchers, an untreated brain herniation can result in the rapid progression of HACE which will then lead to coma and death (cited in Jensen & Vincent, 2021a). Since HACE mostly occurs 4,000 meters above sea level, a patient may not have enough time to get proper treatment for the illness which contributes to the high mortality rate from the illness.

De-Acclimatization Syndrome

AMS, HAPE, and HACE are illnesses that result from ascending to higher elevations, however, they are not the only types of altitude sickness. Humans can also suffer from the de-acclimatization syndrome, a negative reaction when descending from a high altitude. De-acclimatization occurs when an individual spends a long time, around 6 months or more, at a high altitude and their body becomes acclimated to the conditions in the new environment (He et al., 2013). There are other cases, however, where individuals who spent a few days suffered from light symptoms when descending. This indicates that the severity of de-acclimatization syndrome may depend on an individual’s time spent at high altitudes.

Since de-acclimatization syndrome’s severity varies, there is a long list of symptoms of the illness. The symptoms can include headaches, fatigue, sleepiness, fidgeting, insomnia, memory loss, coughing, sore throat, chest tightness, increased appetite, decreased appetite, diarrhea, constipation, abdominal soreness, arthralgia, and other bodily discomforts (He et al., 2013; Liu et al., 2018). Furthermore, de-acclimatization syndrome requires a long recovery period before all the symptoms subside. Individuals who spent several months can take more than 100 days to recover while those who live at high altitudes for more than 12 months may take a year or more to recover from the sickness. Since their body are acclimated to certain levels, they experience an inverse form of AMS.

Treatment for Altitude Sickness

Individuals can take medications or utilize medical equipment to manage the symptoms of altitude sickness and continue with their ascent. They can use oxygen therapy, portable hyperbaric chambers, nifedipine, acetazolamide, and other pharmacologic measures (Jensen & VIncent, 2021a; Jensen & VIncent, 2021b; Timothy et al., 2022). The best treatment in the case of altitude sickness, however, is prevention. Since the major cause of altitude sickness is the rapid ascent to high altitudes, undergoing acclimatization will allow the body to slowly adapt to high altitude conditions.

Acclimatization involves taking the time to slowly ascend from one altitude to another. Through this, the human body adapts by making changes in the respiratory, and pulmonary systems, improving blood cell production, and efficient release of oxygen (Curtis, 1999). The process will require multiple days wherein individuals will remain at a certain altitude before ascending.  For example, an individual planning to climb from 3,000 meters to 3,500 meters will need to remain at around 3,000 meters for a couple of days before they proceed to 3,500 meters. Going further will also require them to repeat the process, extending their climbing time.  Despite the extensiveness of the process, it is the most effective way to avoid altitude sickness.

Another way to treat altitude sickness is the descent to a lower altitude. According to Jensen & Vincent (2021a,  2021b), descending to 1,000 meters is the most important part of HAPE and HACE treatment. The descent requires a careful approach where the patient avoids exerting unnecessary energy that can worsen their condition. If the patient continues to suffer from the symptoms, they can descend further until they notice an improvement in their condition. Since de-acclimatization is a risk when descending rapidly, patients must refrain from descending too quickly from one altitude level to another.


The human body responds to high altitudes in a variety of ways leading to different forms of altitude sickness. Exposure to sudden changes in altitudes will often result in the manifestation of acute mountain sickness, high altitude pulmonary edema, high altitude cerebral edema, and de-acclimatization syndrome. These illnesses share some similar symptoms and treatment, such as acclimatization and descent, but differ in severity and mortality rate. AMS is a less severe condition that individuals can leave untreated while HAPE and HACE are serious illnesses that can cause death without the proper treatment. Understanding these adverse effects of rapid altitude exposure to bodily functions and human health is significant in acknowledging the limitations of the human body, especially for those who frequently travel to different altitudes.

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Reference List

Curtis, R. (1999). Outdoor Action Guide to High Altitude: Acclimatization and Illnesses. Available at,3%20days%20at%20that%20altitude. Accessed May 1, 2022.

He, B., Wang, J., Qian, G., Hu, M., Qu, X., Wei, Z…Wang, G. (2013). Analysis of High-Altitude De-Acclimatization Syndrome After Exposure to High Altitudes: A Cluster-Randomized Controlled Trial. PloS One, 8(5). Available at Accessed May 2, 2022.

Jensen, D & Vincent, A. (2021a). High Altitude Cerebral Edema. StatPearls Publishing. Available at,fatigue%2C%20and%20altered%20mental%20status.. Accessed May 1, 2022.

Jensen, D & Vincent, A. (2021b). High Altitude Pulmonary Edema. StatPearls Publishing. Available at Accessed May 1, 2022.

Liu, HS., Yang, XR., Liu, L., Qin, XK., & Gao, YG. (2018). A Hypothesis Study on a Four-Period Prevention Model for High Altitude Disease. Military Medical Research 5(1). Available at Accessed May 1, 2022. (2018). Altitude Effects on the Human Body. Army Public Health Center. Available at Accessed May 1, 2022.

Scott, B. (2018). How Does Altitude Affect the Body? Murdoch University. Available at,maintain%20a%20neutral%20energy%20balance.. Accessed May 1, 2022.

Turner, R., Gatterer, H., Falla, M., & Lawley, J. (2019). High-Altitude Cerebral Edema: Its Own Entity or End-Stage Acute Mountain Sickness. Journal of Applied Physiology. Available at Accessed May 1, 2022.

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