Why are cells damaged when you don't get enough oxygen?
Oxygen deprivation triggers a chain reaction that damages cells through energy shortage, lactate accumulation, collapsing mitochondria, and programmed cell death. Brain cells and blood vessels are the most vulnerable; protection starts with restoring the oxygen supply as quickly as possible.
Oxygen is the fuel for the cell's efficient energy factory: the mitochondria. Without enough oxygen, cells switch to an emergency method that produces far less energy and leaves behind large amounts of lactate as a waste product. In the cells lining the inner wall of blood vessels, this immediately leads to an energy shortage.
The accumulated lactate then triggers a chain reaction. It binds to a protein that drives glycolysis, making that protein more stable and further amplifying the emergency method. At the same time, the lactate damages the mitochondria of muscle cells in the blood vessel wall: these become too permeable, leak genetic material, and send an alarm signal that pushes the cell toward self-destruction. This turns into a self-reinforcing vicious cycle.
Brain cells are exceptionally sensitive to this process because they have almost no energy reserves. Oxygen deprivation activates multiple damage pathways simultaneously: programmed cell death, disrupted waste processing, DNA damage, and mitochondrial failure. In addition, it damages the blood-brain barrier: a sealing protein in the walls of the brain's blood vessels shifts from its normal position, allowing harmful substances to enter the brain. With prolonged oxygen deprivation, the brain's own immune system also becomes overactive, which amplifies the damage further and can cause cognitive decline.
Mitochondria normally have a built-in quality control system: damaged ones are split apart and broken down, while healthy ones are fused together. A regulatory protein that governs this splitting becomes chemically dysregulated under oxygen deprivation, causing damaged mitochondria to accumulate. This plays a role in damage to the heart, brain, and other organs.
A special case is oxygen deprivation in tumours: cancer cells adapt to it by activating pathways that actually suppress cell death. This makes them more resistant to radiation and chemotherapy, complicating treatment. During pregnancy, oxygen deprivation in the placenta can lead to a specific form of cell death in which fat molecules are oxidised; the damaged cells then release harmful substances into the bloodstream, which damages the mother's blood vessels.
All findings are based on mechanistic and cellular research (in vitro and in vivo), largely in humans or in human cell lines. The chain lactate → mitochondrial damage → cell death has been described consistently across multiple studies. There are no large clinical trials; the molecular mechanisms are plausible but have not yet been fully translated into therapeutic applications.