Telomerase is an enzyme that counters telomere shortening by providing DNA to rebuild telomeres.

Normally, when a cell divides it loses part of its telomeres. As the cell continues to divide it ages and eventually dies when it reaches its Hayflick limit, i.e., its telomeres become too short and replication is no longer possible.

However, cells with telomerase don't lose telomere length as fast or at all. In fact, some cells with telomerase grow longer telomeres despite cell division. The result is cells that bypass their Hayflick limit, with some even becoming "immortal".

Cells that are known to have higher levels of telomerase are:

  • younger cells (to help them survive to maturity);
  • embryonic stem cells (which need to divide indefinitely in order to create a human being);
  • heart cells;
  • blood cells;
  • immune system cells (which need to multiply practically nonstop as they continually fend off disease); and,
  • sperm and eggs cells (which need to survive indefinitely in order to be passed to the next generation or, more broadly, to prevent extinction of the species).

From an anti-aging perspective, telomerase has generated tremendous excitement. Many have speculated that by activating this enzyme in all cells humans can retard the aging process. Some have speculated that telomerase may enable people to live 1,000 years.

The big problem facing telomerase therapies is that, while telomerase may extend the life of cells beneficial to good health, it's also the fuel that enables cancer cells to thrive.