Every day, our bodies replace billions of cells. As cells grow old, they die to make way for the new. This is one of our most crucial bodily processes, which zombie cells disrupt.
Zombie cells are damaged cells that refuse to die. They’ve entered a state of, what scientists call, cellular senescence, one of the nine fundamental hallmarks of aging1. These troublemakers are known contributors to several age-related diseases including arthritis, several cardiovascular illnesses, and cancer2.
Cellular senescence is essentially a brake system; it prevents further cell replication and triggers apoptosis (programmed cell death). Each cell replication damages the cell. And damaged cells replicate to form more damaged cells. This can lead to a host of problems, including cancer.
A typical human cell can divide up to 40 – 60 times before it’s too damaged to replicate. At this point, the cell enters senescence, a zombie-like state. This state prevents further cell replication, and eventually triggers apoptosis.
Senescence is an entirely natural and harmless phase as long as it’s followed by apoptosis. Unfortunately, some of these cells refuse to conduct apoptosis, creating senescent, or zombie, cells. And senescence without apoptosis leads to crisis!
A cell goes zombie after it’s taken excessive DNA damage. Traditionally, senescence occurs after a cell has hit its maximum cell divisions, and should stop replicating. This is referred to as replicative senescence3.
Stress-induced senescence is a more problematic variety. DNA stressors, such as free radicals and UV radiation, attack our DNA, creating breaks. (Read more about using antioxidants to fight free radicals here! )In response to this damage, our cells activate a pathway that prematurely sends it into senescence4,5.
Senescent cells want to get caught. That’s why they’re so obnoxious! They actively secrete toxic inflammatory factors and send signals to neighboring cells to alert the immune system. Ideally, our immune cells would spot the misbehavior and clear the zombies out. Unfortunately, our immune system depletes with age, so many cells don’t get cleared away5.
When these little zombies aren’t stopped, they continue to secrete inflammatory factors leading to chronic inflammation. Chronic inflammation results in the clotting of the bloodstream and brain vessels; it also promotes tumors and neurological disorders6.
Zombie cells also employ cellular signaling to peer-pressure nearby cells towards senescence. As young and impressionable cells, stem cells are particularly influenced by this signaling. In extreme cases, these cells are driven towards senescence en masse, and reservoirs of stem cells deplete significantly. This depletion is a crucial aging instrument, and can even lead to organ dysfunction4.
Free radicals and radiation exposure are huge culprits behind DNA damage and stress-induced senescence. You can actively avoid cellular senescence by using sunscreen and integrating antioxidants, to counter free radicals, into your diet.