Telomeres. These are long stretches of DNA at the ends of our chromosomes, which protect our genes from damage or improper regulation. One Nobel Prize-winning scientist who studies telomeres has compared them to aglets -- the plastic or metal sheath covering ends of shoelaces. When aglets wear down, the shoelace is exposed to fraying and degradation from environmental forces.

Colored in blue are the 46 chromosomes of the human genome.
In white are the telomeres at the end of each chromosome.

Like aglets, telomeres don't last forever. In most of our cells, telomeres get shorter each time that cell divides. And when they get too short, the cell either quits dividing or dies.

Many studies -- in laboratory animals and humans -- have associated shorter telomeres with poor health outcomes, especially in adults.