A simplistic view of telomere length seems to be percolating into the public view of aging, judging by some of the recent discussions on the topic I've encountered. The average disinterested fellow in the street might now have the idea that telomeres somehow get shorter and in doing so cause aging. I expect that this mistaken echo from the halls of science will be reinforced as new telomere assessment services flush with venture funding continue to publicize themselves via the mainstream media.
In fact, telomere length is fairly dynamic and varied, and a lot of uncertain remains in its role in aging. In immune cells the average telomere length seems to correlate well with general health on a statistical basis across a population, being on average shorter in ill people. There are ways to measure telomere length in some animal species that do a good job of predicting likely life expectancy. Delivering additional telomerase, the enzyme that lengthens telomeres, to mice increases their life span. Nonetheless, it's very much up in the air as to whether reduced telomere length is a cause of aging versus a secondary effect of other processes that nonetheless causes some harm of its own, versus just being a marker of the progression of degenerative aging. That telomerase therapy might be extending life through some unrelated function of telomerase, perhaps one involving reducing the level of mitochondrial damage in cells.
Of the mechanisms of aging cataloged in the SENS rejuvenation research proposals, only cancer prevention involves telomeres. All of the other ways in which your metabolism becomes damaged over time have nothing much to do with telomere length. But here is a recent article on science and longevity that focuses on telomeres:
[Telomeres are] tiny structures at the ends of your chromosomes that keep them from fraying and losing crucial bits of genetic information. What interests researchers who study aging is that when cells divide, their telomeres get shorter. Once they get too short, cells stops dividing and may die. Played out across the whole body, there's mounting evidence that shorter telomeres translate into increased susceptibility to diseases and the gradual wearing out of tissues that is the hallmark of old age.
It's tempting to think of our telomeres as the cellular equivalents of the grim reaper's hourglass, counting out our predetermined life spans. But the hourglass can get periodic refills - thanks to an enzyme called telomerase, which acts to build telomeres back up. And the rise of telomere testing for consumers is also pegged to evidence that telomere length is not just an inherited inevitability but may be influenced by factors such as stress, exercise and nutrition. The thinking is, if you can regularly monitor your telomere length, you'll be more apt to do the right things to slow the rate at which they're burning away.
Despite media reports, telomeres do not actually tell you how long you are going to live. That's because there's a huge variation between individuals. A teenager can have shorter telomeres than a 70-year-old, yet that teenager is far more likely to still be around in 20 years. The correlation between telomere length and lifespan is something that emerges when larger numbers of individuals are analyzed as a group.
With the field still trying to figure out exactly how telomeres relate to aging and health, some researchers express strong reservations about telomere testing for health assessment - and taking tests at face value. "It's easy to get correlations in aging, because many, many things are affected as you get older," says David Harrison, a gerontologist at the Jackson Laboratory in Bar Harbor, Me. While he doesn't rule out that telomeres play a role in aging, he is not persuaded that their role is clear or that telomere testing is meaningful. And he is wary, he says, when researchers in the field have a commercial interest in the testing technology.