Every year, 98 percent of the atoms in your body get replaced. This has been known since the 1950s, when researchers actually fed test subjects radioactive atoms and watched their course through the body.

Since atoms make up molecules, and molecules make up cells (which make up tissues and organs), it would seem, then, that our bodies should “refresh” themselves each year in the ultimate of makeovers, leaving us eternally young.

In reality, this “extreme makeover” only goes so far. While your atoms are, indeed, replaced, the structures made of those atoms -- your cells -- are not so invincible.

Your cells regenerate constantly. Among those that regenerate themselves weekly or monthly (red blood cells, for instance), copying mistakes can pop up. And among those that regenerate more slowly (your heart, brain and bones), the cells are susceptible to damage by environmental factors (toxins, radiation and more).

This is why we age, even though our atoms are “new.” That said, your body does have a remarkable capacity to heal itself and age gracefully, living to a ripe old age -- if you give it the right tools.

NPR July 14, 2007