What Can Our Telomeres Tell Us?
Buzzy new DNA tests claim to reveal how "old" our bodies really are.
Telomere mania has spawned a flurry of articles in publications like the Independent, the Huffington Post, and the New York Times, as well as breathy TV spots, like this one from ABC World News, which uses these tests as an occasion to pose the eternal dorm-room puzzler: If you could, would you want to know when you're going to die? Telomeres even got a shout-out on the new Starz show Torchwood: Miracle Day, about a day when everyone in the world stops dying—although their chromosomal ends continue to shorten.
But what exactly can telomere tests tell us about health or aging? The evidence here is still on the young side, though much of it is intriguing. Strong data show that those with extremely short telomeres are more likely to suffer from certain relatively rare age-related diseases, such as bone marrow failure and pulmonary fibrosis. A number of studies also suggest correlations between shorter telomere lengths and higher risk of more widespread ills, including heart disease and cancer, though the evidence here is not unequivocal. Other papers find suggestive connections with stress. In 2004, for instance, researchers looked at women caring for sick children and reported that those who'd been doing so for the longest time tended to have the shortest telomeres relative to other people their age.It's possible, then, that telomere length will prove a useful marker for particular kinds of poor health or adversity—a warning or record etched in DNA.
It's still not clear what that means, though, for the telomere tests now on the market, or those coming soon. These tests generally compare an individual's telomere lengths to reference values from others of the same age. This seems reasonable, because on a population level, telomere length decreases as people get older. The problem is that "at any given age, there's a huge amount of variation" among individuals, says Peter Lansdorp, a professor at the University of British Columbia in Canada and founder of the company Repeat Diagnostics, which provides telomere measures mainly for research and does little marketing to the general public."It's not hard to find a teenager whose telomeres are shorter than [those of] a 70-year-old." Companies also use different methods for assessing telomere length, which can make their results difficult to validate or even compare, he adds. In other words, while the basic concept has promise, using telomere results today to predict an individual's future health or mortality remains tricky business. (Even some enthusiasts, like Blackburn, have pushed back against the wildest claims that telomere lengths can suggest how long an individual has left to live.)
Nor is it clear that, even at their most promising, telomere lengths will prove better predictors of mortality than other, simpler measures. Researchers have studied the telomeres of elderly Danish twins, for instance, whom they followed over time. They found that for pairs of fraternal twins, the one with the shorter telomeres was somewhat more likely to die first. But then some of the scientists wondered if another marker of biological age might prove equally informative. So they conducted another study on "perceived age." That is, they took photos of the twins' faces and asked neutral observers to guess how old each one was. As it turned out, the twin who was thought to look older was also more likely to die first. In other words, if you want to predict a person's health and survival, a picture works about as well—or perhaps slightly better—than telomere length, one of the researchers told me. And the picture is cheaper, to boot.
The poet Randall Jarrell once famously protested that his face belied his true age: "I'll point to myself and say: I'm not like this./ I'm the same as always inside./ – And even that's not so." But maybe Jarrell had it wrong, to the dismay of anyone frowning into the mirror: Maybe the aging face isn't such a liar, after all.
Amanda Schaffer is a science and medical columnist for Slate.
Photograph of woman looking in a mirror by Guang Niu/Getty Images.