Why breathing too much oxygen can lead to health problems? Scientists finally figured out why

Scientists have long known that breathing air with oxygen levels higher than the standard 21 percent found in Earth's atmosphere can cause organ damage, seizures and even death in humans and animals, but they have never been able to find the cause.

According to media reports, in April 2023, in the journal Molecular Cell, the Gladstone Institute revealed how excess oxygen levels change certain iron- and sulfur-containing proteins in our cells, similar to the process of iron rusting. As a result, these "rusted" proteins trigger a chain reaction that damages cells and tissues, shedding light on the impact on diseases such as heart attacks and sleep apnea.

How oxygen is transported in the human body

Oxygen, with the chemical formula O2, makes up about one-fifth of Earth's atmosphere. It is essential to animal life and is used by the mitochondria in nearly all animal cells to convert food into useful energy.

The oxygen dissolved in the blood only accounts for a small part of the blood oxygen content, about 1.5% of the total, and more oxygen is transported through the blood through chemical bonding. There is a component in the blood called hemoglobin. When the blood undergoes gas exchange in the lungs, the oxygen in the air will combine with hemoglobin to form oxygenated hemoglobin.

What would happen to humans if the Earth continued to be in an oxygen-rich environment?

Oxygen enrichment is the process of collecting oxygen from the air using physical or chemical methods so that the oxygen content in the collected gas is ≥21%.

Our health will be seriously threatened. We all know that once the oxygen concentration is lower than 10%, our breathing will become very difficult, consciousness will gradually disappear, and we may die in a few minutes. But when the concentration is too high, the body cannot bear it, and various organs in our body, such as the retina and lungs, will have problems. Even if we can tolerate an oxygen-rich environment, our life span will be shortened. Therefore, although humans cannot live without oxygen, they cannot accept an oxygen-rich environment.

Hypothesis on the origin of oxygen

Scientists have given us several hypotheses about the origin of oxygen.

In 2013, researchers studied fossilized sterols, an organic compound that ancient fungi can produce using extremely low concentrations of oxygen. Based on this, they inferred that oxygen existed on Earth in ancient times.

In 2015, Professor Tian Shanxi of the University of Science and Technology of China and his research team found that there were more carbon dioxide and low-energy electrons in the early Earth's atmosphere. These carbon dioxide molecules can capture low-energy electrons and undergo chemical reactions to produce carbon atom anions and free oxygen atoms or oxygen molecules. After further experiments, they found that oxygen molecules can only be produced within a specific energy range, and that free oxygen atoms as reaction products may also combine into oxygen molecules.

In 2016, according to a report by Huanqiu.com, a research team from Osaka Sangyo University in Japan and others observed oxygen in the early formation of the universe. The study showed that oxygen did not appear immediately after the Big Bang, but was formed inside stars that appeared later and released into the universe through the explosion of stars.

There is also a theory that bacteria are related to the Great Oxidation. About 2.5 billion years ago, the Earth's crust cooled, and the number of anaerobic methanogens also decreased. The oxygen in the air finally escaped the "clutches" of methane, and the oxygen content in the air increased significantly afterwards.

Comprehensive sources:

Science and Technology Daily

Science Popularization China