What causes iron to rust, butter to become rancid and apples to turn brown?
What also messes with your DNA, weakens your memory and hastens aging?
What's this terrible stuff?
It's oxygen, the most common chemical element found on Earth. And its the most common chemical in your body - your life depends on it.
This "most precious" of commodities can also be very hazardous to your health.
This danger comes from the atomic structure of this colorless, odorless, tasteless gas.
In its normal form, an atom of oxygen is surrounded by a cloud of eight electrons - tiny particles of matter carrying a negative electric charge. Usually two such atoms are locked together in a safe, stable oxygen molecule containing a nice even number of electrons. Sometimes, however, one of these electrons is knocked off, or an extra one tacked on, creating a highly unstable molecule known as a "free radical."
Many things can do this - cigarette smoke, smog, ultra-violet rays, the environment, even ordinary food processing can be the culprits, turning oxygen from friend to foe.
Free radicals, like molecular terrorists, roam through living cells, creating havoc. Desperate to regain their regular complement of electrons, they snatch one from any available molecule, starting a chain reaction of devastation. This accumulation of damage - known as "oxidative stress " - is blamed for a multitude of maladies, from cataracts to muscle loss to cancer and PSP.
As researchers' understanding of free radicals grows, they are learning how the body protects itself against their assaults and what kinds of drugs or dietary supplements can help.
A typical human cell generates about 1 trillion oxygen radicals every day as a natural by-product of normal life processes, according to Richard Weindruch at the University of Wisconsin in Madison, an authority on free radicals. About 2 percent of them, or 20 billion toxic molecules, get loose and can be "very dangerous," he said.
"Our bodies can repair much of this damage," Weindruch said.
"Unfortunately, our ability to repair free radical damage decreases with age, and we make more free radicals as we age. Thus the damage accumulates."
Brain cells burn huge amounts of oxygen and therefore are "particularly vulnerable to damage caused by free radicals," said Roberta Brinton, a researcher on aging at the University of Southern California in Los Angeles.
"Oxidative damage is proposed to be one of the early events leading to Alzheimer's disease."
It is also believed to be a cause of Progressive Supranuclear Palsy.
The body's natural defenses against oxidative stress are the so-called antioxidants, small molecules that scavenge for free radicals, donate electrons to them and render them harmless. A perpetual battle is raging in your body between antioxidants and toxic radicals, but eventually the attackers usually overwhelm the defenders.
"Antioxidant defenses are not 100 percent efficient," said Barry Halliwell, a biologist at the University of California at Davis.
Common antioxidants are vitamins A, C and E, found in fruits and vegetables, and the hormone melatonin. Estrogen replacement hormones for post-menopausal women may also protect against the ravages of free radicals.
Health food stores and popular diet books have touted the value of antioxidants ever since their role was discovered a generation ago. Many scientists believe a healthy diet provides most people with all the antioxidants they need, but recommend special supplements, especially Vitamin E, for the elderly.
"The benefit of natural antioxidants is so clear that you should listen to your mom and eat more fruits and vegetables,"said Yang Fann, a researcher at the National Institute of Environmental Health Sciences in Research Triangle Park. Scientific trials to test the value of dietary supplements have been inconclusive. Some have shown that excessive amounts of some vitamins can do more harm than good.
Another way to combat the assault of free radicals may be to cut down on your food intake. In theory, fewer calories should lower the level of oxidative stress, according to Weindruch, and retard the damage associated with increasing age.
Experiments with flies, mice and rats show that reducing the number of calories they consume prolongs their lifespan by as much as 40 percent. In a long-running experiment, George Roth, a molecular biologist at the National Institutes of Health, is feeding monkeys a diet containing 30 percent fewer calories than they would eat on their own. So far they seem healthy, but the effect on their lifespan won't be known for years.
