oxidative stress
/ OK-sih-day-tiv stress /
Think of how a cut apple slowly turns brown, or how iron left in the rain rusts. Both are reactions with oxygen that damage the material. Inside your cells, a related kind of chemical wear-and-tear is constantly going on, and when it gets out of hand it is called oxidative stress. It is the situation in which a cell produces more reactive, damaging oxygen-based molecules than it can safely neutralize.
Cells normally generate small amounts of reactive oxygen species (ROS) — unstable molecules such as the superoxide radical and hydrogen peroxide — mostly as byproducts of making energy in the mitochondria. To keep them in check, cells run a defense system of antioxidants: small molecules like glutathione and vitamins C and E, plus protective enzymes such as superoxide dismutase and catalase that disarm ROS. Oxidative stress arises when the balance tips, either because ROS production surges (from pollution, radiation, infection, or toxins) or because the antioxidant defenses falter. Unchecked ROS then attack the cell's own building blocks: they oxidize lipids in membranes, damage proteins, and mutate DNA.
Oxidative stress is implicated in aging and in many diseases, including cancer, cardiovascular disease, and neurodegeneration, which is why antioxidants get so much attention. But the popular story is too simple. A modest level of ROS is not just tolerated but useful — cells use ROS as signaling molecules and immune cells use them as weapons against microbes. This is why flooding the body with high-dose antioxidant supplements has generally failed to deliver the promised health benefits in large trials, and in some cases even caused harm. The goal in a healthy cell is balance, not the total elimination of oxidants.
A lung cell exposed to cigarette smoke is flooded with reactive oxygen species faster than its antioxidant enzymes can mop them up. The excess ROS oxidize fats in the cell membrane and nick the DNA. Repeated bouts of this oxidative stress, year after year, are one reason long-term smoking damages tissue and raises cancer risk.
Oxidative stress is too many reactive oxygen molecules for the cell's defenses to handle.
More antioxidants is not automatically better. Cells need some reactive oxygen species for signaling and immune defense, and large trials of high-dose antioxidant supplements have largely failed to extend life or prevent disease — sometimes doing harm.