This article will give you a simple explanation of what hypoxia and oxidative stress are and how they are connected. By understanding these points, you will grasp how vital adequate oxygenation is for our health and the importance of balancing free radicals and antioxidants in our bodies (read on to find out about those, too).

What is hypoxia?

Hypoxia is a condition where oxygen is deficient in the tissues and organs of the body. Oxygen is crucial for cells to produce energy, so a lack of oxygen can cause various problems.

Causes of hypoxia

A lack of oxygen in the body can be caused by several things. We can categorise these into environmental causes, medical conditions, and situational causes of hypoxia. A common example of an environmental cause of hypoxia is being exposed to high altitudes, as the air has less air pressure and oxygen. Many respiratory conditions will be associated with hypoxia, like asthma and chronic obstructive pulmonary disease (COPD). Other conditions contributing to hypoxia include heart disease and anaemia. Finally, strenuous exercise or choking would be examples of situational hypoxia. 

Types of hypoxia

The mechanisms of breathing and respiration involve several steps, and any of these steps can be affected.¹ If there is insufficient oxygen entering the airways, then this is known as hypoxic hypoxia. It can be due to the environment, as mentioned above, or issues with the airways, such as an obstruction. Next, we have anaemic hypoxia. People with anaemia do not have enough haemoglobin in the blood to carry oxygen. So, although enough oxygen enters the airways and the lungs, the amount of oxygen being transported around the body is still insufficient. The third type is circulatory hypoxia (also known as stagnant or ischaemic hypoxia), and this is the result of poor blood circulation, so oxygen can be carried by the blood, but it isn’t delivered well. The fourth type of hypoxia occurs when cells and tissues can't use the oxygen because of toxins (e.g., cyanide poisoning). This is known as histotoxic hypoxia. 

When the body doesn't get enough oxygen

• Energy production decreases: normally, cells produce energy (known as ATP) through aerobic respiration, using oxygen. Without enough oxygen, cells switch to anaerobic metabolism, which is much less efficient.² Aerobic respiration produces about 36 ATP molecules per glucose molecule, while anaerobic respiration produces only about 2 ATP molecules per glucose molecule
• Lactic acid buildup: Anaerobic metabolism leads to the accumulation of lactic acid in the tissues. Blood lactic acid levels can rise significantly during hypoxia, potentially leading to lactic acidosis if levels exceed 4 mmol/L
• Brain sensitivity: The brain is extremely sensitive to hypoxia. Brain cells begin to die within 5 minutes of oxygen deprivation. Studies indicate that for every minute a stroke goes untreated, the brain loses an estimated 1.9 million neurons³
• Organ damage: Prolonged hypoxia can lead to organ damage and failure. For instance, heart tissues can sustain irreversible damage after about 30 minutes of severe oxygen deprivation, which is why prompt treatment of heart attacks is critical⁴

What is oxidative stress?

Oxidative stress occurs when there is an imbalance between free radicals (unstable molecules that can damage cells) and antioxidants (molecules that neutralise free radicals). Free radicals are produced naturally in the body during normal metabolic processes but also from external sources like pollution, radiation, and tobacco smoke. Antioxidants are found in foods (e.g., fruits, vegetables, nuts) and produced by the body. They neutralise free radicals.

How do hypoxia and oxidative stress interact?

There are detailed mechanisms and explanations of hypoxia and its relation to oxidative stress. In summary, when cells are starved of oxygen, they produce more free radicals. Free radicals cause damage to cell membranes, proteins, and DNA. The balance of free radicals and antioxidants is essential because if the body’s antioxidants can't keep up with the free radical production, oxidative stress occurs.

Why are hypoxia and oxidative stress important?

Both hypoxia and oxidative stress are linked to cardiovascular diseases, stroke, and cancer.⁴ Moreover, they play a significant role in neurodegenerative diseases such as Alzheimer's and Parkinson's disease. Chronic conditions like COPD and heart disease often involve ongoing hypoxia and oxidative stress, accelerating ageing and furthering disease progression.⁵ Understanding these mechanisms highlights the importance of maintaining healthy oxygen levels and a balanced diet rich in antioxidants to mitigate these risks and promote overall well-being.

Summary

Hypoxia is a condition where the body’s tissues and organs receive insufficient oxygen, leading to decreased energy production, lactic acid buildup, and potential organ damage. It can be caused by environmental factors, medical conditions, or situations like exercise or choking. There are different types of hypoxia, including hypoxic hypoxia, anaemic hypoxia, circulatory hypoxia, and histotoxic hypoxia, each involving different mechanisms of oxygen deficiency.

Oxidative stress occurs when there is an imbalance between free radicals, which damage cells, and antioxidants, which neutralize them. Hypoxia can increase free radical production, contributing to oxidative stress, which damages cell membranes, proteins, and DNA. Both hypoxia and oxidative stress are linked to cardiovascular diseases, strokes, cancer, and neurodegenerative diseases like Alzheimer's and Parkinson's. Chronic conditions such as COPD and heart disease can involve prolonged hypoxia and oxidative stress, accelerating disease progression. Maintaining proper oxygen levels and a balanced diet rich in antioxidants is vital for health.