Needs - Air and Water

 What does your body really need to survive? What are the limits of your endurance? How much can you stand without water? Do you need anything else to survive?

Air is the most urgent human need - we need an almost continuous supply of this mixture of atmospheric gases. The most important component for humans is oxygen, the nominal volume concentration of which in the air is 20.95%. According to the health and safety standards of various countries, the optimal oxygen content is in the range of 19% - 23.5%. Above this range, oxygen becomes toxic to humans - the number of free radicals in the body increases, leading to oxidative stress. However, don't panic - a few puffs of pure oxygen will not hurt you. Toxicity appears after exposure longer than one day.

Oxygen deficiency becomes noticeable when its concentration in the air drops below 15%. With a value of less than 10%, serious disturbances of consciousness, including fainting, are possible. Strangulation may occur below 8%. We rarely wonder about this question, unknowingly assuming that the oxygen content in the air is always constant. However, there are a few cases where this is not the case, such as heating rooms with open fire or evaporation of liquefied gases (for example LPG). But most of all, the oxygen content depends on the height above sea level.

Although the oxygen volume concentration in air is more or less constant, it should be remembered that the amount of oxygen taken up by the lungs decreases with increasing altitude. This is due to the falling atmospheric pressure, which translates into lower oxygen partial pressure, making it more difficult for the lungs to take the same amount of the life-giving element. Already at a thousand meters above sea level, the amount of oxygen consumed by the body drops to 18.4%. In two thousand it is the value of 16.3%.

The highest permanently inhabited town in the world is La Rinconada in Peru, at 5,100 meters above sea level, where the amount of oxygen absorbed by the lungs is estimated at about 11% - almost half less than above sea level.

Living at such an altitude is possible, although it can cause chronic mountain sickness (CMS), also known as Mong's disease. Some communities that have lived at high altitudes for many generations have evolved a genetic response to these conditions. Interestingly, different groups have developed different mechanisms - Tibetan Sherpas breathe more often and deeper, and have wider blood vessels. The Andean tribes of the Quechua Indians have an increased amount of red blood cells and hemoglobin in their blood, and the Ethiopian highlanders have better blood oxidation thanks to the mutation of one gene (the gene encoding the B endothelin receptor - ERTB).

The lower safety limit, i.e. the altitude up to which symptoms of oxygen deficiency do not occur, has been set at 2,500 m above sea level. To such values, the pressure in airplanes is set in the case of flight at high altitudes. Above this height, some people may experience the first symptoms of altitude sickness. The body is able to adapt to new conditions in a process known as altitude acclimation. The safe rate of acclimatization was determined to be 300 meters per day plus one additional day every 900 meters. Since the body's response to altitude is very individual, many people are able to acclimatize much faster. Acclimatization has its limits, but it is difficult to determine exactly what is the maximum altitude at which the human body can function normally for an extended period of time. The record holders are miners working in the Aucanquilcha sulfur mine in Chile, located at 5,950 meters above sea level, who spent 2 years there.

Staying above 6,000 meters is extremely difficult. The death zone - the altitude at which it is extremely dangerous for the human body has been conventionally set at 8,000 meters above sea level. (you also find a value of 25,000 feet, or about 7,600 meters, or 26,000 feet, or about 7,900 meters.) You can spend a maximum of several hours at this height. One of the record holders is the climber Lincoln Hall, who fainted while descending Mount Everest and was left behind by his companions at an altitude of about 8,600 meters. Night fell and Hall was presumed dead. 12 hours later, a group of climbers attacking the summit, to their surprise, found a climber alive who was aware and fit enough that the group managed to bring him down. Hall survived and, save for a few frostbites, fully recovered.

Sudden changes in the oxygen level are a big challenge for the body, which it cannot always cope with, which can be manifested by acute altitude sickness (AMS - accute mountain sickness). Personally, I experienced such a change when I reached an altitude of four thousand meters (Hilo - Mauna Kea) from sea level within two hours. In just a few minutes, the lack of oxygen was clearly felt - tinnitus, headache, confusion, feeling unreal, color vision disturbance. After returning to normal altitude, all symptoms disappeared.

The record holder withstood one breath of atmospheric air for 11 minutes and 54 seconds (as of May 2020, the record set by Branko Petrovic, October 7, 2014 in Dubai). There are people who lasted even more than 20 minutes, but with the use of pure oxygen, so I omit their performance. The average person is able to hold on for about a minute on one breath, and then there will be a reflex to breathe in. Even if we were extremely strong-willed and choose not to breathe, all we can do is lose consciousness, and then breathing will return to normal. By the way, a curiosity - mammals, including humans, are equipped with a diving reflex that activates special adaptive mechanisms during immersion. As a result, breathing is uneven - we are able to withstand water longer with one breath than on "dry land". The factor that mainly triggers the diving reflex is immersion of the face in water at a temperature below 21 degrees Celsius.

But how much will we be able to endure if we are unable to breathe due to external causes? For most people, this time will be between 3 and 5 minutes, but keep it as low as possible, 3 minutes. After this time, ATP, the molecular fuel of the cell, is depleted, which causes its death. The critical organ here is the brain, which has enormous energy needs and it will be the main victim of hypoxia. Brain death is assumed to occur six minutes after oxygen supply is stopped. However, there are known cases of prolonging this time many times, related to staying in a low temperature. This mainly applies to people who fell into ice-cold water. An example is Anna Bågenholm, who fell into a frozen lake during a ski accident. Anna breathed in the air that was stuck under the ice for 40 minutes, then lost consciousness and her heart stopped beating. She spent another 40 minutes in this manner, after which she was pulled out and taken to the hospital in Tromsø. Her body temperature was 13.7 degrees Celsius. Doctors fought for her life for nine hours. Anna awoke from her coma ten days later, spent two months in the intensive care unit, but finally managed to recover almost completely.

There is another risk associated with cold water - thermal shock. If we suddenly find ourselves in cold water, our first impulse will be to take a breath. This reflex is so strong that it occurs even when fully submerged, so we draw water into our lungs and sink rapidly. It was the thermal shock that was the main cause of the death of the helicopter crews, which fell into the sea as a result of the accident. This problem is particularly acute in the North Sea region, where up to one hundred flights a day take place. Currently, each passenger is equipped with a small oxygen cylinder, with a reserve sufficient for a few minutes of breathing, but a few years ago, the standard equipment included an air pocket (Rebreather), used to breathe one's own air. The instructions were simple - just before descending, take a deep breath and activate the rebreather. In this way, the exhaled air got into the pocket and was used for breathing. The concept of breathing your own air seems a bit pointless at first, but the main goal here is to deal with the gasp reflex during a thermal shock.

In the event that we are not fully submerged and our head is above the surface of the water, thermal shock is equally dangerous as it can lead to hyperventilation and a phenomenon called respiratory alkalosis - the sudden removal of carbon dioxide from the body, causing the blood pH to rise. Respiratory alkalosis can lead to unconsciousness and, consequently, drowning. An extreme case is falling into a frozen lake. In such cases, it is important to remember that there are very effective methods of self-help.

One note - this technique is good for exiting an ice hole, which is where the adjacent ice is thick enough not to collapse further. If we are dealing with a thin layer of ice that breaks below us, the technique will be slightly different - do not get up right away, just crawl over to the more stable part and only get up there.

The most obvious answer is under water. The second thing that comes to mind is high altitude. But there are a few more places where the oxygen content may be below the safe minimum. Particularly dangerous are closed, tight spaces, professionally known as confined spaces, which include: tanks, silos, sewage wells, canals, septic tanks, wells, tunnels or shafts. Heavy gases can accumulate there, which, due to gravity, push the air upwards. Keep this in mind whenever you want to see what is at the bottom of a dry well. Most often, we won't find anything interesting there, and we can come across an invisible killer in the form of lack of oxygen.

However, don't panic if you get stuck in an elevator or a car. In both cases, we will not run out of oxygen, because these spaces are not tightly closed and there is always at least a minimal air circulation that is enough for us to survive. Strong emotions are always a bad counselor, and it is no different in this case: the heart rate increases, breathing speeds up and hyperventilation may occur, which further exacerbates the panic. In this way, we fall into a spiral of fear that takes away our ability to think logically and can cause us even more trouble. Maintaining calm and sober thoughts in life-threatening situations is a critical skill.

To sum up: the time we can spend without access to air is 3 minutes.

Water is the third most urgent human need (right after air and warmth). Water is a basic component of the cells of the human body and is essential for its functioning. The entire process of transporting nutrients and cellular respiration takes place in the aquatic environment. Water has a number of functions in the human body, and it would take a long time to list the reasons why optimal water levels are critical. Water is brought into the body through the digestive system in the form of fluids and food - food itself contains water, and quite a lot of it - fruits and vegetables, for example. In addition, the body "produces" water as a result of metabolic processes, obtaining it precisely from food. Therefore, when speaking of the body's need for water, it is necessary to distinguish between the total demand for water from all sources and the demand for drinking water.

This is basically a simple question, there is no single answer and depends on many factors - age, gender, physical activity, health, and environmental temperature. Even if we narrow down our question to a specific case, for example, a 40-year-old healthy man weighing 90 kg, staying at room temperature, working in an office and having low physical activity - the answer is still not straightforward. Different countries' ministries of health give different values. Let's take a look at how much water Mirosław should drink, according to the standards recommended by some countries and organizations (source Scientific Opinion on Dietary Reference Values ​​for Water):

• Belgium (2009) - total consumption from all sources - 2.5 L, fluid consumption - 1.5 L.
• Austria, Germany, Switzerland (2008) - 1 mL for every kilocalorie consumed. A 90-kilo man with little physical activity needs about 2,200 - 2,500 kcal per day, so the daily water requirement will be 2.2 - 2.5 L.
• France (2001) - between 25 and 35 mL for every kilogram of body, i.e. 2.25 - 3.15 L per day from all sources. Assuming that the body produces 300 mL of metabolic water and obtains 1,000 to 1,200 mL of food, you should drink 1 to 1.9 liters of water daily.
• Denmark, Finland, Norway, Sweden (2004) - 30 mL for every kilogram of the body, which in our case is 2.7 liters per day from all sources.
• Netherlands (1989) - with a normal diet, the amount of water you drink should be 1.5 liters per day. The minimum amount is defined as 1 liter per day.
• USA (2004) - the total water demand for our case amounts to 3.7 liters per day. For women, 2.7 liters.
• World Health Organization (WHO, 2003; 2005) - total water requirement - 2.9 liters per day. Women - 2.2 liters.

The spread is quite large - the total water demand of our Miroslaw ranges from 2.2 (Germany) to 3.7 liters (USA) per day. Assuming that the body gets 1.3 liters of water from food, it turns out that you should drink between 0.9 and 2.4 liters of water a day.

Remember that the need for water will be higher if we sweat more - during physical exertion, in hot climates, in stressful situations, when working in all kinds of overalls and work clothes, poorly ventilated rooms, etc. Also in cold climates we need more water, because higher energy expenditure of the body requires more of it, and at high altitudes, which is associated with greater loss of water through the lungs.

The recommendation is for the total amount of water you consume from all sources. Be careful, as it is easy to confuse this with the amount of water you drink, resulting in incorrect recommendations. An example may be a wrong infographic from the National Center for Nutrition Education.

The standard is correct, but the infographic does not take into account that we also get water from food and incorrectly suggests the number of glasses recommended.

Yes, of course. There are many risks associated with too much water in the body, but the most important thing is hyponatremia, i.e. a decrease in the sodium content in the blood serum below 130-135 mmol / L. This causes a disturbance of the cellular osmotic balance, which leads to the movement of extracellular water inside the cell, thereby increasing its volume. This is especially dangerous in the case of the brain, where the increase in cell volume can lead to swelling (yes, if you drink a lot of water, your brain will explode 🙂)

How much water is that? Many countries (including Austria, Germany and Switzerland) have a fluid limit of 10 liters per day. Medical reports on water intoxication report values ​​such as: 5 liters in a few hours (source), 6 liters in three hours (source), or 1.9 liters per hour for several hours (source).

Under normal circumstances, no one would think of drinking that much water, but the situation changes when exercising - then we drink much more. While the problem is not with a normal training session, which usually lasts no longer than two or even three hours, the danger is with extreme efforts such as ultramarathons and triathlons, especially in hot and humid climates. Then the players drink up to 1.5 liters of water per hour, which leads to rapid loss of sodium in the plasma and the development of exercise-associated hyponatremia (EAH), which can lead to the death of the player. During strenuous efforts, one should drink isotonic solutions, ie solutions in which the concentration of "osmotically active" compounds is similar to their concentration in the blood plasma. What does it mean? According to the report of the European Commission for Health and Consumer Protection (source), the concentration of sodium in an isotonic drink should be 20-50 mmol per liter, ie 460-1150 mg per liter. The simplest source of sodium is table salt - NaCl, with 1 gram of salt containing 393.4 milligrams of sodium. To meet the above recommendation, 1 - 3 grams of table salt (1.17 - 2.92 g to be exact) should be dissolved in one liter of water. It should also be remembered that sodium is not the only element that should contain water or an isotonic drink. This consideration leads us directly to the next point:

What water should I drink?

What exactly is water? From a chemical point of view, it is the liquid form of hydrogen oxide (the term oxidate is also used). Since water is a good solvent, its pure form does not exist on Earth. Even distilled water is not 100% pure. There will always be some chemical contamination, but that's not bad news for us. In the course of evolution, living organisms have learned to trap these pollutants and use them as food. An example is the above-mentioned sodium, the source of which are various water-soluble minerals, mainly halite (i.e. table salt). A brief repetition of chemistry - a given compound, after being dissolved by water, breaks down into ions - a positive ion, i.e. a cation, and a negative ion, i.e. an anion. In the case of table salt, i.e. sodium chloride NaCl, this compound is broken down into the sodium cation Na + and the chloride anion Cl-. If we look at the packaging of any mineral water, we should see the full ionic composition of the water.

What should you pay attention to? First of all, the overall mineralization, i.e. the total content of minerals. This is the main parameter for classifying water. There are several ways to classify waters, and each one uses a different terminology. In geological terms, mineral water must contain more than 1000 mg of ions per liter - hardly any water meets this condition. Most of the waters sold are either acratopegs with a mineralization between 500 and 1000 mg / L, or freshwater (<500 mg / L).

Since the first mineral bottle was placed on the store shelf, a discussion has arisen as to what water to drink, whether high or low-mineralized; whether with high or low sodium content; or a French brand that sounds "naive" when read backwards, or one from the Polish mountains. Each producer makes a theory - if their water is low in sodium, it writes that it is good for people with hypertension; if it is high in sodium, it is perfect for exercise. The same goes for absolutely every other ingredient. Which water to choose? In our opinion, it does not matter. As long as it's not a heavy caliber in the form of Zuber water with a mineralization of 24,000 mg / L, it doesn't make much difference what we drink. If you want to be absolutely sure that you will not hurt yourself by drinking the given water, then aim for the acratopega (500 - 1000 mg / L). So much for this topic.

Of course, we recommend that you give up all kinds of carbonated, sweetened and energetic drinks - they have no health benefits. The exception is good isotonic drinks, which are essential during prolonged exercise. For additional drinks - tea, coffee, possibly 100% fruit juice, preferably squeezed. But in fact, water should be your staple drink.

By the way - a quick explanation of what the "stone" in the kettle is. Well, the water, seeping through the layers of limestone, with the participation of carbon dioxide dissolves the main component of these rocks - calcium carbonate, i.e. calcite. Calcite breaks down into two ions: the calcium cation and the bicarbonate anion. Calcite has the specific property that it dissolves better in cold water than in warm water. Therefore, it will precipitate in the opposite way to most known substances - in warm water. Therefore, it is made at the bottom of the kettle and not in a jug of cold water. And no, the stone is not harmful - it makes no difference whether you drink it dissolved in water, or scratch it with a spoon from the bottom of the kettle and eat it - anyway, it will go to your body, which is very fond of the components of the stone, i.e. calcium and magnesium cations.

This leads to the next point - water hardness. Simply put, water hardness is the degree of mineralization, i.e. the content of ions, mainly calcium and magnesium. Hard water, although not very beneficial for household appliances and hindering the action of detergents, is certainly not harmful to health, on the contrary, because it contains more minerals that are beneficial for the body. Speaking of mineralization, let's look at two extreme cases - distilled water and seawater.

Can i drink distilled water?

Generally yes, but keep in mind that distilled water contains almost no minerals and will therefore reduce their concentration in the body. It is not a dangerous process, as long as we have access to a balanced diet or supplement the minerals with supplements. However, you should not drink distilled water during strenuous exercise, as it accelerates sodium leaching and may lead to the already mentioned hyponatremia. Of course - distilled water is better than no water at all - you are much more likely to die from dehydration than from hyponatraemia.

Can i drink sea water?

No, drinking seawater leads to a phenomenon called hypertonic hyperhydration. There is a phenomenon opposite to hyponatremia - hypernatremia, i.e. an increase in plasma sodium concentration above 145 mmol / L. The reverse process occurs - this time the intracellular water migrates outward, causing the cell to dehydrate. The body, detecting too much sodium in the blood, will try to reduce its concentration. One of the steps will be to increase your thirst as fresh water is the simplest medicine. However, this leads to a very dangerous loopback - if we are shipwrecked at sea and we drink sea water due to enormous thirst, the thirst will soon be even greater. The body has gotten too much sodium and will try to dilute it by demanding fresh water. Each sip of seawater only makes things worse - even more sodium, stronger thirst and stronger intracellular water migration. Extremely dehydrated nerve cells have serious problems with working properly - there are hallucinations, confusion, over-excitation, convulsions and finally coma. The circulatory system reacts in a similar way - congestive heart failure appears, which is dangerous for life. Drinking seawater while not having access to freshwater very quickly can lead to death!

Recently, I have noticed that many people fear thirst like fire and drink water compulsively to avoid dehydration. I hear words repeated like a mantra almost everywhere: "stay hydrated." I have seen many articles saying that the mechanism of the feeling of desire is very imperfect, works too late, and is easy to deceive. And yet this mechanism is the result of an extremely long evolution, thanks to which almost 8 billion people on Earth now live. If it worked poorly, it would mean that thousands of generations lived in a permanent state of dehydration, which I don't really want to believe. There are scientific studies that show that dehydration even at the level of 2.6% does not lead to a significant decrease in concentration or mood.

The article also suggests that the water regulating mechanism is very precise and complex. In addition, the body is able to suggest to the awareness what it lacks. This is especially true of sodium - when plasma levels drop, the body craves salty drinks.

Of course, you should drink water regularly and stay hydrated. It's more about psychological comfort - your body is designed so that a slight dehydration will not cause severe health complications, so don't panic if you don't take a bottle of water for a long walk.

How much can a person survive without water?

Death from dehydration occurs when water is lost over 15% of body weight. Our exemplary Miroslaw, weighing 90 kilograms, could therefore lose a maximum of 13.5 liters of water.

The minimum loss of water under ideal conditions is 1 liter per day. However, it should be emphasized here that these are ideal conditions: there is no sweating and the person does not move at all. In such conditions, our Mirosław could survive for almost two weeks. However, normally a person loses much more water - as much as the daily requirement, i.e. between 2.2 and 3.7 liters per day. Taking the lower value, Mirosław's survival rate drops to six days. In the case of the upper value - three and a half days. However, we are still talking about normal conditions - if we lack water, it means an extreme situation, such as complete paralysis of the state, war or getting lost in the wild. In such scenarios, we move more, sweat more, and breathe faster, so it should be assumed that water loss will be even faster. How fast? It depends, mostly on the climate. In case of extreme temperatures, a person can sweat as much as 10 liters of water a day (source), so Mirosław would last almost a day and a half. In the case of a milder climate, this time is longer, but it must be assumed that an adult, fit person, without access to water, can survive no more than three days.

Assume that you will probably live without water for 3 days.