Oxygen is essential for survival to ensure that cells function and produce energy. Without enough oxygen, the body's organs and cells die. However, scientists have found that limiting oxygen intake at certain times may actually help the body better repair injuries.
In fact, the human body does have mechanisms to cope with different oxygen concentrations. Preliminary research has found that in the state of hypoxia, some special cell differentiation and metabolic mechanisms in the human body will be activated, thereby helping to treat certain diseases and enhance human health.
However, the deep life mechanism of hypoxia is still poorly understood. In-depth study of the benefits and disadvantages of hypoxia to the human body will help improve human health and overcome more diseases.
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For climbers Ralph Duimowitz and Nancy Hansen, who have climbed eight of the world's tallest mountains together, the thin air environment doesn't seem like much of a problem. In May 2018, the two of them entered the low-oxygen chamber of the German Aerospace Center, the "highest peak" they have climbed in their careers.
After a two-week acclimatization period, they persevered for 16 days in an environment thinner than the air at the summit of Mount Everest, including four days with oxygen concentrations equivalent to being in the mountains at an altitude of 7,112 meters above sea level – very close to the "death zone" at 8,000 meters above sea level. In the "death zone," the lack of oxygen affects climbers' judgment and increases their risk of heart attack and stroke.
Throughout the experiment, the two climbers and the researchers who observed them hesitated countless times to interrupt the experiment. But the good news is that they persevered. If Duimowitz and Hansen can show that humans can tolerate prolonged periods of hypoxia, it could pave the way for a more ambitious experiment: testing whether people deprived of oxygen for a period of time is good for their bodies.
High altitude adaptation
Or can it make your body healthier?
This sounds a little strange. Because our organs and tissues need oxygen. In the early days of the 2020 coronavirus pandemic, patients' blood oxygen levels were so low that doctors were confused, so they added a "polyoxygen" to their treatment plan. Similarly, people with heart disease or stroke need oxygen after an attack to make sure their tissues don't die.
Still, scientists have found that some hypoxic adaptations appear to be beneficial. About 140 years ago, French physiologist Paul Burt put forward the hypothesis that "in a high-altitude environment, the number of red blood cells carrying oxygen in the body will increase". Air Force pilots in the '30s were trained to "adapt to high altitude" before flying open cockpit aircraft.
During this time, doctors noticed that hypoxia seemed to help treat everything from asthma to high blood pressure. There are still many clinical phenomena that show that when a person's heart and spinal cord are damaged, appropriate hypoxia may help patients recover faster.
In fact, our bodies have long been prepared to adapt to different oxygen concentrations. The 2019 Nobel Prize in Physiology or Medicine was awarded to three British and American scientists who discovered a key molecule called hypoxia-inducible factor (HIF), which is produced in large quantities when oxygen supply is insufficient, helping the body cope with hypoxia by activating hundreds of genes and biochemical signaling pathways.
Scientists have wondered: Are we breathing in too much oxygen in some cases? This seems to be completely different from the traditional medical view of hypoxia: when people enter the mountains, the reduced oxygen supply forces the body to respond to measures such as a rapid heartbeat and an increase in blood pressure. People may experience nausea, headaches, and difficulty concentrating. Severe altitude sickness can also be fatal because it causes the brain to swell and fluid to build up in the lungs.
Still, those at higher altitudes appear to be healthier than those who live at lower altitudes for a long time — diabetes, cardiovascular disease, and certain cancers (such as breast cancer and lymphoma) have lower rates among them at lower altitudes.
Intermittent hypoxia
May trigger growth factor release
Some animal studies have revealed the reasons behind this paradox. In 2017, Hisham Sadiq and colleagues at the University of Texas Southwestern Medical Center in Dallas reported a strange finding.
The researchers kept the mice in a space where oxygen levels were gradually decreasing, and found that after breathing 7% oxygen (equivalent to the amount of oxygen people breathe at the summit of Mount Everest) for two weeks, the heart cells of these mice began to divide and grow again. This is a surprising finding, because adult mammalian hearts often fail to form enough new tissue to regenerate themselves, which is why heart disease is so deadly.
Sadiq knew that mammalian heart cells were able to divide and grow in the womb, but that ability was lost soon after birth. He wondered if it had something to do with the special oxygen environment that embryos experienced.
While embryos get oxygen from their mothers through the placenta, their hearts grow largely in hypoxic conditions, when the heart can regenerate if damaged. However, babies lose this ability soon after birth, and when they start breathing, their bodies are filled with oxygen. Sadiq speculates that the process is reversible: by finely controlling the concentration of oxygen inhaled, mature heart cells may revert to an "embryonic state" and regain the ability to divide and regenerate.
Sadiq isn't the only one who has discovered that hypoxia can be beneficial. For the past few years, a team led by Gordon Mitchell, a neuroscientist at the University of Florida, has been limiting oxygen intake for spinal cord injury patients. These patients all need to be on ventilators, Mitchell said: "We will have patients inhale one minute of normal air, another minute of thin air equivalent to the mountains at an altitude of 6,000 meters, and so on." ”
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The study found that patients who breathed thin air were less dependent on ventilators. At the same time, their ability to walk and grasp has improved. Mitchell's team found that hypoxia triggers the release of growth factors, which enhance neural connections — and that in turn, the neural pathways between the brain and spinal cord are strengthened. Now, this finding is being confirmed by more clinical trials.
There is also some evidence that hypoxia stimulates the growth of new blood vessels around the heart. This may help explain why people who live at high altitudes for a long time have a lower risk of cardiovascular disease.
Several preliminary trials have been published so far, and intermittent hypoxia therapy may also help reduce cognitive impairment associated with neurodegenerative diseases. Mitchell revealed that they are also studying the effects of intermittent hypoxia therapy for other diseases, including amyotrophic lateral sclerosis, multiple sclerosis and stroke.
Stay in the mountains
Eating more without moving can also burn more fat
For healthy ordinary people, hypoxia treatment may also have many benefits, one of which is more attractive to the public is to help lose weight.
Studies have shown that people who live at high altitudes are generally not obese, and people who live at low altitudes and regularly engage in mountaineering are not prone to obesity. Is this because people who like to live at high altitudes are more active? Or is it because climbing mountains is an energy-intensive sport? But the researchers say there may be deeper reasons beyond that.
In 1985, the U.S. military conducted a 40-day simulation of a mountaineering expedition in a hypoxic chamber. The six volunteers are warmly dressed, have unlimited snacks and meals each day, and can exercise if they wish. As in Duimowitz and Hansen's experiments with DLR, the oxygen content in the cabin gradually decreases until it is as thin as the summit of Mount Everest. Experiments showed that volunteers lost an average of 7.5 kg in 40 days.
Another study yielded similar results. The researchers recruited a group of obese men and asked them to spend a week in a comfortable residence located at an altitude of 2650 meters. During this time, the volunteers did not exercise and could eat as much as they wanted, but each lost about 1.3 kilograms.
Researchers believe that hypoxia leads to weight loss in two ways. The first is to make people less hungry. In the study, the researchers found that the volunteers produced more satiety hormones at high altitudes, so they ate 730 fewer calories per day than usual during the trial. The second is to trigger hormonal changes that increase the body's metabolic rate. In a state of hypoxia, the body burns more calories and consumes at least 30% more energy.
Use a double-edged sword
Explore "Healthier with Thin Oxygen"
That's not to say that anyone who wants to lose weight should go hiking. On the one hand, the effects of hypoxia may subside when people are no longer deprived of oxygen – a weekend at a ski resort is unlikely to produce lasting weight loss. On the other hand, existing research is unclear about exactly how much oxygen inhalation should be restricted to have positive health effects, and whether appropriate restriction of inhaled oxygen is appropriate for everyone.
At the end of the day, hypoxia can be a double-edged sword: beneficial in some cases, undoubtedly harmful in others. For example, for people with sleep apnea, lack of oxygen causes people to stop breathing repeatedly during the night, sometimes for up to a few minutes. Many people with sleep apnea syndrome develop diabetes, possibly because lack of oxygen triggers changes in glucose metabolism that make patients more susceptible to diabetes.
Research on hypoxia needs to continue, hence the experiments that Duimowitz and Hansen received. Inspired by Sadiq's mouse study, which showed that hypoxia promotes the regeneration of heart cells, DLR's Ulrich Limbel and his colleagues wanted to test the effects of chronic hypoxia on healthy individuals first, and eventually in people recovering from heart disease.
The thin air causes visible changes in the climber's body: their heartbeat becomes irregular, their blood thickens because of the extra red blood cells produced by the bone marrow, veins in the brain swell, the heart contracts, and the heart wall thickens. When they return to breathing normal air, most of these changes are reversed.
For their part, Duimowitz and Hansen seemed relieved when they stepped out of the windowless hypoxic chamber and returned to normal air. Hansen wrote on her blog: "After five weeks in a hypoxic chamber, my first impression after leaving the cabin was that it was big and busy. There was a lot of oxygen in the air, it felt great! ”
More in-depth research will continue. Limbel said: "Now that we know that healthy individuals in humans can tolerate this level of hypoxia without risk, we need to prove that heart disease patients can too." His team has recruited a group of volunteers with heart disease who are willing to spend weeks in hypoxic chambers — like climbers, volunteers go through a process where ambient oxygen levels slowly drop.
Oxygen is an irreplaceable substance that human beings rely on for survival. Because it's so important, Limbel hopes to find a way for the body to fight back when there is a lack of oxygen—people become healthier when oxygen is thin.