Why some people get very old and others die at an early age have puzzled us for a long time. We try all sorts of things to slow down the ageing process and increase our longevity. But how do we know what works and what doesn’t? Ageing can be considered as a progressive failure in the ability to maintain tissue homeostasis, leading to health decline and the emergence of age-related disease. In the words of Wong 2001; Kirkwood 2005; Schmidt et al. 2005 – “The process of aging is regarded as a progressive functional decline, which can be observed in cells, tissues and organisms, and which results in an increased vulnerability to environmental challenge and a growing risk to suffer disease and to die.”

The history of the ageing theory

In 1908 Rubner published his famous work noting the duration of animal lifespan and its relationship to energy expenditure. The free radical, nowadays called the oxidative stress or the rate of living theory of ageing, took Rubners ideas further and was proposed some 60 years ago. It suggests that a lower metabolic rate means longer life span and higher metabolic rate means a shorter life span, i.e. “live fast, die young”.

Larger animals in general have a low metabolic rate and tend to live longer than smaller animals with a corresponding higher metabolic rate. One explanation for the difference in metabolism is that all species lose heat through the skin and since small animals have more skin surface in relation to their body size, they lose more heat than larger animals. Because of this they need a higher metabolism to produce the heat needed to keep a body temperature of 36-38 degrees Celsius, since this temperature is optimum for protein performance.

A good example is an elephant. It can live up to 80 years and since it has a slow metabolism, the elephant heart beats roughly the same number of beats as the heart of a mouse. The mouse however, with a much faster metabolism, “uses up” it’s heart beats in only 2-3 years.

A number of studies have shown that calorie constriction leads to increased life span, which seems to confirm the oxidative stress theory of ageing, since calorie restriction reduces the metabolism. However, it may also be that these animals that are put on restricted diets are just surviving, but not thriving. Like a bear hibernating, it has very low metabolism, but doesn’t really get much done.

A factor speaking against the theory, or atleast indicating that it is incomplete, is that there are several exceptions. For example birds live longer than their similar sized mammals. Or the fact that physical exercise, which increases metabolism, doesn’t lead to shorter life span.

Below are three more interesting connections in regards to ageing:

1. Carbon dioxide increase fat burning and antioxidant activity through the peroxisomes

The peroxisome is an organelle working very closely with the mitochondria. When the carbon dioxide levels are low, there is less activity in the peroxisomes. The peroxisomes do a lot of important activities, but these are the three major functions:

Control mitochondrial biogenesis (size and number of mitochondria) through the peroxisome PGC-1? pathway. When PGC-1? is activated it stimulates mitochondrial growth. In this cancer-study: Transcutaneous Application of Carbon Dioxide (CO2) Induces Mitochondrial Apoptosis (Ref 1), rats had cancer-cells injected. In one group the rats were exposed to CO2 through the skin. 100% CO2 was administered into a bag that covered the tumor, for 10 minutes twice per week for two weeks. In total 40 minutes, which is not a lot. Despite the tiny CO2 exposure, the tumor volume was reduced by 48% compared to the control group. The researchers concluded that CO2 activated the PGC-1? pathway and hence increased the mitochondrial activity, which in turn made the mitochondria induce apoptosis.

(size and number of mitochondria) through the peroxisome PGC-1? pathway. When PGC-1? is activated it stimulates mitochondrial growth. In this cancer-study: (Ref 1), rats had cancer-cells injected. In one group the rats were exposed to CO2 through the skin. 100% CO2 was administered into a bag that covered the tumor, for 10 minutes twice per week for two weeks. In total 40 minutes, which is not a lot. Despite the tiny CO2 exposure, the tumor volume was reduced by 48% compared to the control group. The researchers concluded that CO2 activated the PGC-1? pathway and hence increased the mitochondrial activity, which in turn made the mitochondria induce apoptosis. Convert long fatty acids to Acetyl-CoA , so that the Acetyl-CoA can be fed to the mitochondria for conversion to ATP, heat, water, CO2 and free radicals. In contrast to normal length fatty acids, these long fatty acids can’t be burnt directly in the mitochondria, but instead needs to pass through the peroxisomes for conversion first.

, so that the Acetyl-CoA can be fed to the mitochondria for conversion to ATP, heat, water, CO2 and free radicals. In contrast to normal length fatty acids, these long fatty acids can’t be burnt directly in the mitochondria, but instead needs to pass through the peroxisomes for conversion first. Neutralize free radicals. The conversion-process from fat to Acetyl-CoA generates the free radical hydrogen peroxide (H2O2). Consequently, the peroxisomes contain the enzyme catalase, one of the fastest enzymes in our body. Catalase can convert millions of hydrogen peroxide into water and oxygen per second. In other words, catalase is a powerful antioxidant that can neutralize large amounts of free radicals.

In conclusion, the information above means that low CO2 not only lead to reduced mitochondria, as the PGC-1? pathway is downregulated in low CO2, but low CO2 also reduces the size and number of peroxisomes, and thereby decreased ability to burn fat and reduced antioxidant activity, which in turn contributes to increased oxidative stress and a shorter life span.

From one perspective cancer could be viewed mainly as an ageing disease (although some young people also get cancer). Since cancer is very much associated with a) poor mitochondrial function, b) high sugar metabolism and c) oxidative stress, the link between low CO2, peroxisome and mitochondria dysfunction is indeed interesting.

2. Carbon dioxide deficiency may reduce heat production

Another interesting aspect of ageing is uncoupling, which is the ability for the mitochondria to switch to produce more heat instead of ATP-energy. Uncoupling seems to produce fewer free radicals even when metabolism is higher.

So, for example if we over breathe or over eat, more oxygen and/or more nutrients than needed in order to meet the metabolic demand, may reach the cell. The mitochondria can then uncouple and produce heat instead of ATP energy. However, if our ability to uncouple is diminished, the mitochondria will be flooded with oxygen and/or nutrients in overeating / over breathing, and it will leak more free radicals.

Here is an interesting article on the subject: Body size, energy metabolism and lifespan: (Ref 2) – “However, smaller individuals with higher rates of metabolism live longer than their slower, larger conspecifics. An addition to these confused observations has been the recent suggestion that under some circumstances we might expect mitochondria to produce fewer free radicals when metabolism is higher–particularly when they are uncoupled. These new ideas concerning the manner in which mitochondria generate free radicals as a function of metabolism shed some light on the complexity of observations linking body size, metabolism and lifespan.”

A factor that increase the ability to uncouple is the circulation to the skin. If the circulation is good, the extra heat produced in uncoupling can escape through the skin. However, if the blood circulation to the skin is not so good, which is the case when CO2 is low, it may lead to problems with uncoupling. Below we discuss heat production and circulation to the skin in relation to thyroid function.

3. Membrane fatty acid composition correlates with maximum lifespan

The organelles in our cells (mitochondria, nucleus, peroxisomes etc.) are highly specialized and can be likened to rooms in a house – kitchen, bedroom, toilet, living room etc. Just as the house have outer walls to protect the house from the weather and unwelcome guests and inner walls to separate the rooms from each other, the cell has an outer wall, the cell membrane, to protect the cell from virus, bacteria and unwanted substances and the organelles have walls as well, mitochondrial membrane etc, to separate the organelles from each other.

The cellular and organelle membranes are made up of fatty acids. The correlation between membrane composition and longevity is called the membrane pacemaker theory of ageing and the lipid peroxidation index. The theory states that in general polyunsaturated fatty acids (PUFA) are more susceptible to oxidative stress than saturated and monounsaturated fatty acids. It also seems evident that the more omega 6 polyunsaturated fatty acids (in relation to omega 3), the shorter the lifespan. For humans, omega 6 is to be found in junk food. Here are some interesting articles on the subject:

Explaining longevity of different animals: is membrane fatty acid composition the missing link?: (Ref 3) “ Saturated and monounsaturated fatty acids are very resistant to peroxidative damage, while the more polyunsaturated a fatty acid, the more susceptible it is to peroxidation. Membrane fatty acid composition is correlated with the maximum lifespans of mammals and birds. Exceptionally long-living mammal species and birds have a more peroxidation-resistant membrane composition compared to shorter-living similar-sized mammals. Membrane fatty acid composition is little appreciated but important correlate to the rate of aging of animals and the determination of their longevity .”

(Ref 3) “ .” The importance of the ratio of omega-6/omega-3 essential fatty acids: (Ref 4) “ Several sources of information suggest that human beings evolved on a diet with a ratio of omega-6 to omega-3 essential fatty acids (EFA) of approximately 1 whereas in Western diets the ratio is 15/1-16.7/1. Western diets are deficient in omega-3 fatty acids, and have excessive amounts of omega-6 fatty acids compared with the diet on which human beings evolved and their genetic patterns were established. Excessive amounts of omega-6 polyunsaturated fatty acids (PUFA) and a very high omega-6/omega-3 ratio, as is found in today’s Western diets, promote the pathogenesis of many diseases, including cardiovascular disease, cancer, and inflammatory and autoimmune diseases, whereas increased levels of omega-3 PUFA (a low omega-6/omega-3 ratio) exert suppressive effects .”

(Ref 4) “ .” Oxidative Stress and Lipid Peroxidation Products in Cancer Progression and Therapy: (Ref 5) “The lipid peroxidation and the breakage of lipids with the formation of reactive compounds can lead to changes in the permeability and fluidity of the membrane lipid bilayer and can dramatically alter cell integrity.”

We can’t live without oxygen

The reason why we only survive a few minutes without breathing is because of energy deficiency. The oxygen that we inhale is needed in order to produce energy efficiently. With the aid of oxygen we can extract up to 100% of the available energy in the food we eat, while only 6% of the energy can be extracted without oxygen.

This says a lot about how important oxygen is for our survival. But even though we are so extremely dependent of oxygen we store very little of it at any given time. At rest we consume about 250 ml of oxygen per minute, so even if we were able to use up all of the approx. 1,6 liter of oxygen that we store (for a 70 kg person), which we probably can’t, it will still only last for about 6-7 minutes (Ref 6).

So why do we have so little oxygen? In comparison to the approx. 120 liter of carbon dioxide that we store, the amount of oxygen is 75 times less. It is because oxygen is so reactive and too much of it is dangerous and toxic (leads to oxidative stress), so we can only allow some of the oxygen to reach the mitochondria at any given time.

The vast majority of our energy, 90%, is produced in the mitochondria in the cells. The mitochondria are often likened to an incinerator and it is easy to understand the danger of oxygen if we think of spraying it on a normal fire. When the oxygen hits the fire, the reaction will be very explosive. That’s why the energy production in the mitochondria is divided into several steps, so that there won’t be any “oxygen explosions”.

Carbon dioxide paves the way for oxygen

The major function of breathing is to inhale oxygen and exhale the carbon dioxide produced in the metabolism process. And it is easy to think of oxygen as the lifesaver and CO2 as the waste product. But it is actually the other way around.

It is carbon dioxide that paves the way for oxygen, all the way from initiating the inhale of air (through the phrenic nerve that signals to the diaphragm to move downwards), to kicking off the oxygen from the blood at the cellular level.

Inhale: CO2 tells the brain stem, by lowering the pH to the level where the breathing center is triggered to start an inhalation.

CO2 tells the brain stem, by lowering the pH to the level where the breathing center is triggered to start an inhalation. Airways: CO2 makes the smooth muscles in the airways relax so that they can open up and let the air into the lungs.

CO2 makes the smooth muscles in the airways relax so that they can open up and let the air into the lungs. Blood: CO2 makes the smooth muscles in the blood vessels relax so that they open up and circulation can occur easily.

CO2 makes the smooth muscles in the blood vessels relax so that they open up and circulation can occur easily. Cells: According to the Bohr-effect CO2 lowers pH, which reduces hemoglobin affinity for oxygen and the O2 is released from the blood to the cells.

In conclusion, an optimum carbon dioxide pressure is needed in order to oxygenate our body in the most efficient way.

Too many free radicals equals oxidative stress

For every cycle that the electron transport chain runs in the mitochondria, in order to produce the energy we need to survive and thrive, it will also produce free oxygen radicals. Free radicals are not bad per se, instead they make up an important signal pathway that are involved in for example cell division and angiogenesis (the process where the capillary network increases, so that the cell can get more blood, oxygen and nutrients and remove waste).

This is logical, since if we exercise, the metabolism increases, and more free radicals are formed, which leads to increased cell division and angiogenesis that is needed in order to meet the increased demand from the cell.

The problem arises when we have an excess of free radicals, either because too many are formed or because the antioxidant system that is supposed to neutralize the free radicals, is compromised. Too many free radicals is also called oxidative stress.

Reduced thyroid function when carbon dioxide is low

So in conclusion oxygen is a double edged sword, where too little leads to death and too much increases free radicals and oxidative stress.When we over breathe the carbon dioxide pressure in our body decreases, which have a negative impact on circulation since CO2 widens the blood vessels. In poor circulation our body prioritizes blood flow to the most important organs – kidneys, lungs, heart and brain. The first organ to receive less blood is the skin, followed by our muscles.

In thyroid problems it is common that the skin is dry, irritated and coarse, which indicates that the blood circulation to the skin isn’t optimum. When this happens, two important negative effects happen. The first is that it is harder to tolerate heat. Since our skin is responsible for controlling our body temperature, poor blood flow to the skin creates problems with heat regulation.

So if the body gets too hot it can’t get rid of the excess heat through the skin and our core temperature increases. The only way for the body to compensate for this is by reducing the activity in the thyroid, as the thyroid is responsible for body metabolism and thereby also heat production. So an important reason for an underactive thyroid is to compensate for poor circulation to the skin, which occur because of over breathing that lowers the CO2 pressure, which in turn makes the blood vessels constrict.

Increased soda consumption to increase carbon dioxide

The consumption of carbonated beverages in our society is very big. Why do we like to drink carbonated beverages? A main reason is because they contain CO2, and the increased consumption can be viewed as a result of our body simply recognizing the low levels of CO2 and that they need to be refilled.

And the reason why we prefer a cold soda or beer over a warm one, is because warm drinks lose their CO2 to the atmosphere faster. So when the carbonated drink is warm it contains less CO2 and therefore doesn’t taste as good. The reason we don’t find the taste as appealing is probably because our body doesn’t get the CO2 it is looking for.

Another reason for the big consumption is also breathing related and have to do with our energy production. When we produce energy we can do it in two ways, with our without oxygen. Energy production with oxygen is a complex and fairly slow process, but on the other hand up to 100% of the available energy can be extracted from the nutrients we ingest. Energy production without oxygen, on the other hand, is indeed simple and fast, but only 6% of the available energy is extracted.

When the CO2 pressure is lower the oxygenation is impaired, which forces us to produce more of the energy without oxygen and in the long term use simpler and simpler sources of energy. It is possible that the more often we choose energy sources that are simple for our body to convert to energy, the “simpler” we will over time become as a person. WE need a balance between complexity and simplicity.

Fungi produces carbon dioxide and may increase when the CO2 levels are low

Fungi and their spores are everywhere. They are present in air, so with every breath we inhale hundreds of fungi spores. Although, with nasal breathing we can probably stop most of them from entering the lungs. They are also in the soil forming mykorrhiza – an amazing symbiotic relationship between microscopic fungi spores growing into the roots of trees and plants, heping each other to take up nutrients.

The fungi spores can even be found in rocks. For millions of years they have done an important job in tearing up rocks into smaller and smaller rock crystals until eventually soil has been formed.

Fungi produce carbon dioxide. An effect of over breathing (and inactivity) that decreases the CO2-pressure in our body, could then be that more fungi is formed in order to “try to maintain a normal CO2 pressure and pH”, for example in the skin and gut. A few examples:

Skin infections . The pH of the skin is normally between 4-5. Poor circulation to the skin, because of low CO2, may raise skin pH (as CO2 is acidic), hence provide a favorable environment for fungi and diseases like athlete’s foot, ringworm and other fungal infections of the skin may develop.

. The pH of the skin is normally between 4-5. Poor circulation to the skin, because of low CO2, may raise skin pH (as CO2 is acidic), hence provide a favorable environment for fungi and diseases like athlete’s foot, ringworm and other fungal infections of the skin may develop. Candida . The gut microbiome consists of enormous amounts of bacteria and other micro organisms, and one of these inhabitants is the family of yeast fungi called candida. When the candida get the opportunity they will start to multiply rapidly (the fungi is opportunistic). Candida infections can occur in the mouth, throat, gut and the vagina, and also in the blood.

. The gut microbiome consists of enormous amounts of bacteria and other micro organisms, and one of these inhabitants is the family of yeast fungi called candida. When the candida get the opportunity they will start to multiply rapidly (the fungi is opportunistic). Candida infections can occur in the mouth, throat, gut and the vagina, and also in the blood. Cryptococcus gattii. This yeast is primarily responsible for cryptococcosis, a fungal disease that occurs in about one million HIV/AIDS patients, causing over 600,000 deaths annually.

If you want to learn more about fungi here is a film well worth watching: The Kingdom: How Fungi Made Our World >>

High carbon dioxide levels in social insect colonies

CO2 concentration ranges from 1 to 2 percent in ant colonies, 0.8–5.2 percent in termite colonies and 0.2–9.9 percent in honey bee (Apis mellifera L.) colonies. Even though there is a considerable variation, it by far exceeds the normal levels in the atmosphere of 0,04%. The high CO2-levels could explain why the queen live far longer than her colony workers. Since the queen is in the colony all the time, she is constantly exposed to these high CO2 levels.

THE BEE QUEEN

A bee queen could be three to four years old, compared to a normal bee worker that only live for two to three months, she lives ten to twelve times longer.

Scientists Explore Queen Bee Longevity: (Ref 7) “ The queen honey bee is genetically identical to the workers in her hive, but she lives 10 times longer. Many times the way organisms achieve longevity is via a tradeoff with reproduction,” said entomology professor Gene Robinson, principal investigator on the study. “In general, life forms that postpone reproduction until later in life live longer. But the queen bee has her cake and eats it too. She’s an egg-laying machine. She lays 2,000 eggs a day and yet lives 10 times longer than individuals that stem from the same genome and yet do not reproduce.”

(Ref 7) “ said entomology professor Gene Robinson, principal investigator on the study. Extended longevity of queen honey bees compared to workers is associated with peroxidation-resistant membranes: (Ref 8) “Assuming the same slope of the relationship between membrane peroxidation index and maximum lifespan as previously observed for mammal and bird species, we propose that the 3-fold difference in peroxidation index of phospholipids of queens and workers is large enough to account for the order-of-magnitude difference in their longevity.”

THE TERMITE QUEEN

Termites are among the most successful groups of insects on Earth, colonising all landmasses except Antarctica. The Termite Queen has a long life span. She can live up to 50 years, the longest for any insect. In comparison, termite workers normally live only ont to two years.

Termites have a very organized society – workers are responsible for building the nest and collect dead wood, plants and leaves, soldiers defending the colony, and a queen and king are responsible for reproduction. Termite species in Africa and Asia have been cultivating fungi for consumption for tens of millions of years. And they do it well as the harvest of a colony retain the same high yield level for up to several decades. As mentioned above, the interesting thing is that fungi give off carbon dioxide.

An Efficient Antioxidant System in a Long-Lived Termite Queen: (Ref 9) “ These long-lived queens have a significantly lower level of oxidative damage, including oxidative DNA damage, than workers, soldiers and nymphs. The lower levels of damage appear to be due to increased catalase, an enzyme that protects against oxidative stress .”

(Ref 9) “ .” Sociobiology and Natural Adaptation of Termite and Termitomyces in Different Forest Division of Gorakhpur Region: (Ref 10) “ Some species of Termite practice fungi culture. They maintain a garden of specialized fungi Termitomyces, which are nourished by the excrement of the insect. When the fungi are eaten, their spores pass undamaged through the intestine of the termite to complete the cycle by germinating in the fresh faecal pellets. The termites cultivate the fungus on special structures within the nest called fungus combs. These fungus combs are continuously provided with externally derived plant material (e.g. wood, dry grass, leaf litter), while the older parts, consisting of partially degraded plant material and fungal mycelium and nodules (asexual fruit bodies covered with conidia) are consumed . All species in the genus Termitomyces are completely dependent on the termites since they have never been found free-living and they are rapidly overgrown by other fungi, when removed from the termite nest .”

(Ref 10) “ .” Why exceptionally fertile termite queens have long lives: (Ref 11) “ Usually the rule in the animal kingdom is that a lot of progeny means a short life – if you are less fertile, you live longer. ‘Macrotermes queens are the most reproductively successful terrestrial animals,’ says Freiburg biologist Prof. Dr. Judith Korb. Termite queens lay continuously about 20,000 eggs daily. And yet they reach ages of up to 20 years. Workers from this species have the same genome as the queen, but are infertile and only live for a few months .”

(Ref 11) “ .” The architecture of termite mounds: a result of a trade-off between thermoregulation and gas exchange?: (Ref 12) “ Although termites can, at least for some time, survive under high concentrations of CO2, a colony, with up to 6 million individuals (Lüscher, 1961) and its cultivated fungi, needs a sufficient gas exchange. Lüscher (1961) measured CO2 concentrations of up to 2.8% in the center of M. bellicosus nests, and Matsumoto (1978) recorded concentrations of up to 5.2% in the center of other Macrotermitinae nests .”

(Ref 12) “ .” Termite World | Life In The Undergrowth | Richard Attenborough: “The fungus-growing termite is the most common and widely distributed member of all Macrotermes in southern Africa. They live in nests that are kept at a constant temperature by a remarkable piece of engineering, a spiralled mound consisting of a network of vents and tunnels set around one central chimney. As their names suggests these termites actually cultivate fungus to digest the food which they are unable to do so themselves.”

THE ANT QUEEN

The ant queen can live for up to 30 years, but workers live only one to three years. Apart from humans, ants are the most successful species in spreading around the globe. The tunnel system and space under the visible nest could reach 5-6 meters below ground and have an area as big as a tennis court. Just as termites they have an organized society and many species also cultivate fungus, which give off CO2.

Longevity of harvester ant colonies in southern Idaho: (Ref 13) “ In the ant species, pogonomyrmex owyheei, the queen ant has a maximum estimated longevity of 30 years, while worker ants live only one or two years .”

(Ref 13) “ .” Carbon dioxide concentrations and nest ventilation in nests of the leaf-cutting ant Atta vollenweideri: (Ref 14) “Gas exchange between nest and environment is essential. Due to colony respiration considerable amounts of O2 are consumed and CO2 produced. In closed dwellings this leads to hypoxic (low oxygen) and hypercapnic (high carbon dioxide) conditions.”

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Other land animals with high tolerance for carbon dioxide

One aspect in relation to ageing is the breathing frequency. We know that dogs, cats and mice have a high respiration rate and live a markedly shorter period of time, compared to a giant tortoise that only takes about four to five breaths per minute and can live up to 200 years and an elephant only takes four to six breaths per minute and can become up to 80 years old.

NAKED MOLE RAT

This fascinating little creature can be up to 30 years old, which is 10-15 times longer than their similar sized cousin, the mouse. The naked mole rat lives about a meter below ground, where the oxygen levels are low and the CO2 levels are high. They have a slow respiration, can survive up to 18 minutes without oxygen and suffer from very little oxidative stress.

Weird: Naked Mole Rats Don’t Die of Old Age: (Ref 15) “ ’ The chance of a mole rat dying at one year of age or dying at 25 years of age is the same. We really don’t know what’s killing them at this point .’ Buffenstein told Live Science. It would be like if humans were equally likely to die at 30 as at 90 , she said.”

(Ref 15) “ ’ .’ Buffenstein told Live Science. , she said.” The Naked Mole-Rat Response to Oxidative Stress: Just Deal with It: (Ref 16) “Strikingly, these animals are very resistant to cancer, with no case ever reported in our large colony maintained for over 30 years. This is in sharp contrast to data based upon laboratory rodents. For example, >70% of C57Bl/6 mice die of cancer in the laboratory setting. Not only are naked mole-rats resistant to cancers, but they also appear to resist many of the age-associated diseases. We have found that unlike mice, naked mole-rats show a markedly slower age-related change in diastolic function with approximately a 25% decline over 20 years, whereas the change in diastolic function over a similar proportion of lifespan in C57Bl/6 mice is more than a 50% decline.”

BATS

Bats can live up to 40 years. An important factor why they get so old, despite being so small, is probably because they live in the caves where their own excrement is rich in ammonia. The ammonia escapes into the air and gives rise to the smell characteristic for bat populated caves. Ammonia is alkaline and when inhaling it the bats get alkaline, hence they retain carbon dioxide, which is acidic, in order to cope with the high levels of CO2.

Ageing studies on bats: a review: (Ref 17) “ Bat biologists have long known about the exceptional longevity of bats (Order: Chiroptera), which is unusual for mammals of such a small size and a high metabolic rate .”

(Ref 17) “ .” Ammonia Tolerance of the California Leaf-Nosed Bat: (Ref 18) “ Investigators have often mentioned the extremely unpleasant working conditions in the ammoniated atmosphere of caves and mines frequented by large number of bats…Since this condition occurs in the normal habitat of these animals, interest was aroused regarding their unusual tolerance to ammonia .”

(Ref 18) “ .” Carbon Dioxide Retention: A Mechanism of Ammonia Tolerance in Mammals: (Ref 19) “ Passive carbon dioxide retention is clearly related to ammonia tolerance in these mammals .”

(Ref 19) “ .” Elevated Carbon Dioxide Levels in Bayliss Cave, Australia: Implications for the Evolution of Obligate Cave Species: (Ref 20) “The downward-sloping cave acts as a trap for CO2 , because CO2 is 1.5 times heavier than air. Between The Wall and The Duckunder is a zone of mixing in which the CO2 concentration increased nearly five times (from 0.6 to 2.8 volume %). Beyond The Wall the CO2 increased dramatically to a maximum of 5.9%.”

ECHIDNA

The echidna is a mammal, although it lays eggs. It could be up to 50 years old which is very old for an animal of this size (it’s weight is only about 3-4 kg).

Control of breathing in the echidna during hibernation: (Ref 21) “ Resting non-hibernating echidnas are characterised by low metabolic rates, but also have a very low respiratory frequency and a variable respiratory minute volume, often resulting in low levels of arterial O(2) and high CO(2) .”

(Ref 21) “ .” Respiration by buried echidnas Tachyglossus aculeatus: (Ref 22) “ It is clear that echidnas are frequently exposed, at least for short periods, to increased hypoxia and hypercapnia, either when digging into soil or within their burrows (Augee et al., 1971). Previous studies have demonstrated that echidnas are physiologically well suited for burrowing. Augee et al. (Augee et al., 1971) covered echidnas with soil to simulate natural conditions and found them to be very tolerant of high carbon dioxide (CO2) and low oxygen (O2) under these conditions .”

(Ref 22) “ .” The exceptional longevity of an egg-laying mammal, the short-beaked echidna is associated with peroxidation-resistant membrane composition: (Ref 23) “These findings support the membrane pacemaker theory of aging and emphasise the potential importance of membrane fatty acid composition in aging and in the determination of maximum longevity.”

Other sea animals with high tolerance for carbon dioxide

Creatures that swim the ocean depths are notoriously difficult to observe in their natural habitat, so there is still much to be learned about many species.

Water contains about 50 times higher levels of CO2 than the atmosphere, which may contribute to the long life of many water living species. And cold waters contains even more CO2.

BOWHEAD WHALE

The Bowhead whale can grow 14 to 18 m in length and weigh from 75 to 100 tonnes and they can live over 200 years. They live in the Arctic waters, which has a fairly constant temperature near the freezing point. From a carbon dioxide perspective this is very interesting, as colder water contains more CO2. And this could be an explanation to why the whale lives to such an old age.

Insights into the Evolution of Longevity from the Bowhead Whale Genome: (Ref 24) “It is remarkable that a warm-blooded species such as the bowhead whale (Balaena mysticetus) has not only been estimated to live over 200 years (estimated age of one specimen 211 SE 35 years), suggesting it is the longest-lived mammal, but also exhibits very low disease incidence until an advanced age compared to humans.”

GREENLAND SHARK

Just like the Bowhead whale, the Greenland sharks are native to the Arctic (and North Atlantic). It can grow to be up to 7 meters long and weigh up to 1,200 kilo. One study showed that they live up to 300-500 years.

Eye lens radiocarbon reveals centuries of longevity in the Greenland shark: (Ref 25) “ The Greenland shark (Somniosus microcephalus), an iconic species of the Arctic Seas, grows slowly and reaches >500 centimeters (cm) in total length, suggesting a life span well beyond those of other vertebrates. Radiocarbon dating of eye lens nuclei from 28 female Greenland sharks (81 to 502 cm in total length) revealed a life span of at least 272 years. Our results show that the Greenland shark is the longest-lived vertebrate known .”

(Ref 25) “ .” Longest-lived vertebrate is Greenland shark: Lifespan of 400 years: (Ref 26) “Their analysis suggests an average lifespan of at least 272 years. The two largest sharks in this study, at 493 cm and 502 cm in length, were estimated to be roughly 335 and 392 years old, respectively. Based on these results, the Greenland shark is now the oldest-known vertebrate to roam the Earth.”

ANTARCTICA ISLANDICA

The Antarctica islandica, also called the ocean quahog clam, shows exceptional longevity. One specimen called “Ming” was estimated to live up to 507 years in the wild. The clam has a slow respiration and can tolerate very low levels of oxygen and high levels of carbon dioxide. The shell traps the CO2 inside, similar to the high CO2 levels in a beehive.

The extreme longevity of Arctica islandica is associated with increased peroxidation resistance in mitochondrial membranes: (Ref 27) “ The deleterious reactive carbonyls released upon oxidation of polyunsaturated fatty acids in biological membranes are believed to foster cellular aging. Comparative studies in mammals and birds have shown that the susceptibility to peroxidation of membrane lipids peroxidation index (PI) is negatively correlated with longevity. These results clearly demonstrate that the PI also decreases with increasing longevity in marine bivalves and that it decreases faster in the mitochondrial membrane than in other membranes in general. Furthermore, the particularly low PI values for A. islandica can partly explain this species’ extreme longevity .”

(Ref 27) “ .” Extreme Longevity Is Associated With Increased Resistance to Oxidative Stress in Arctica islandica, the Longest-Living Non-Colonial Animal: (Ref 28) “ Our findings demonstrate an association between longevity and resistance to oxidative stress–induced cell death in A islandica, consistent with the oxidative stress hypothesis of aging and provide justification for detailed evaluation of pathways involving repair of free radical–mediated macromolecular damage and regulation of apoptosis in the world’s longest-living non-colonial animal .”

(Ref 28) “ .” A metabolic model for the ocean quahog Arctica islandica – Effects of animal mass and age, temperature, salinity and geography on respiration rate: (Ref 29) “ Respiration of Arctica islandica is significantly below the average of 59 bivalve species when compared at the same temperature and animal mass .”

(Ref 29) “ .” Metabolic and physiological responses in tissues of the long-lived bivalve Arctica islandica to oxygen deficiency: (Ref 30) “In Arctica islandica, a long lifespan is associated with low metabolic activity, and with a pronounced tolerance to low environmental oxygen.”

Breathe less and live longer

A reason why humans tend to live longer and longer could probably to some extent be attributed to a) increased CO2 levels in the atmosphere, where it has increased by 60% in the last 270 years, from 0,025% CO2 in 1750, before industrialization, to 0,041% in 2019 and b) people spending more time indoors where the CO2 levels in general are higher than outdoors.

The common denominator for the species listed above, all well known for their extreme longevity, is that they have slow respiration and/or high tolerance for carbon dioxide, i.e. suggesting that the carbon dioxide tolerance theory may be the most important factor determining longevity.

For example, the fundamental difference between someone in a state of panic and someone in deep relaxation isn’t first and foremost a question of the quality of their sleep, food, exercise, relationships etc. The fundamental difference is carbon dioxide tolerance. The person with a panic attack has a fast and shallow breathing with a corresponding low CO2 tolerance, while the person in deep relaxation breathe low and slow and have a high tolerance for carbon dioxide.

There are two main ways to increase the levels of carbon dioxide in your body – reduce the outflow and increase the production. When you slow down your breathing less CO2 is lost via exhalation and when you do physical activity, more CO2 is produced as the metabolism increases. A great way is to combine the two, low intense physical activity while only breathing through your nose. Over time the carbon dioxide tolerance training will reset the breathing center in your brain stem and make you tolerate higher and higher levels of CO2, which in turn may help you to live a healthier and longer life.

Scientific References