In fact, the new test represents a difference in degree rather than kind from the individual tests we currently use to assess health, such as cholesterol, triglyceride, and glucose levels. Telomere tests aim to provide a one-stop snapshot of our statistical risk for everything from heart disease and diabetes to cognitive decline and mortality. If people can monitor their telomere length, the thinking goes, they can make lifestyle changes to alter that risk by boosting their cells' longevity.

How it works

How can a simple test that analyzes white-blood cells provide this kind of information?

When cells divide to replicate themselves, their telomeres shorten. That's led many scientists to view telomere length as a marker of biological aging, a "molecular" clock ticking off the cell's lifespan, as well as an indicator of overall health. So, in general, older people have shorter telomeres than younger ones. In February, Ronald A. DePinho, a cancer biologist at Boston's Dana-Farber Cancer Institute, proposed a unified theory of aging, with malfunctioning telomeres as the the "core pathway" causing health decline in advanced age.

But telomere length is just part of the picture.

"Telomere length, like any other risk measurement, tells us probability of disease and early mortality-it is not a diagnosis," stresses Elissa Epel, a health psychologist at the University of California, San Francisco, and a cofounder of Telome Health Inc. (THI), one of the companies offering the test. "Telomere length is only helpful information when interpreted correctly, which is probabilistically," she says.

Here's how that interpretation will work: Like other medical tests based on risk assessments, the companies will compare your telomere length to a "norm" determined through statistical analysis of large groups of people similar in age, gender, and behaviors . Both Meno Park-based THI and Life Length S.L., in Madrid, Spain, are conducting those studies now.

As molecular biologist Calvin B. Harley, chief scientific officer and a cofounder of THI, puts it, "The bottom line is that for every risk factor, it's not a diagnosis or a prognosis; it's a statistical result based upon large group analyses."

Ready or not?

That said, two of the most distinguished researchers in the field who shared the 2009 Nobel Prize for their telomere work—Elizabeth H. Blackburn, a cofounder of THI, and Carol Greider, a molecular biologist at the Johns Hopkins School of Medicine—disagree about the value of a test at this point in time. You've likely heard Greider elsewhere, perhaps in one of those misleading reports. Here she is in context.

Greider doesn't believe there have been enough large-scale clinical studies yet for a telomere-length measurement to give individuals useful information about their risk status. "We've known a lot about cholesterol for a long time, so you can pick out a particular individual and say for this individual we know what the risks are," she says.  "And that's from many different laboratories over many, many years. And so it's established within the scientific community. That is not the current state of the status in terms of telomere length."

Blackburn disagrees. "Multiple cohorts and multiple studies have established clear statistical links with telomere shortness and risks for common as well as less common diseases that include cardiovascular disease and mortality, certain cancers, and diabetes, as well as associations with severe life-trauma exposures that themselves have clearly established risks for diseases," she emails from Iceland, where she is delivering a talk. "These studies include some additional, not yet published,  longitudinal studies that, for example, Carol may not be aware of."

Greider further compares the current state of telomere testing to direct-to-consumer genetic testing, which offers to sequence your genome and tell you your susceptibility to certain diseases. "The concern there has always been: What are they going to tell people about those particular genetic variations" that they find? she asks. "The science isn't there yet" regarding what different configurations of genetic variations mean about predisposition to disease.

Again, Blackburn demurs, pointing out in an email that telomeres, though comprising DNA, do not carry "genetic-information content" like the genome does. Hence, changes in telomere length don't represent variations in genes but rather the aging of cells and how that aging correlates statistically with disease risk.

There's a growing body of research showing correlations between telomere length, particularly white-blood-cell telomere length, and lifestyle. For example, studies show that those who exercise regularly have longer telomeres than couch potatoes. Folks rating highest on a pessimism scale have shorter telomeres than those rating lowest. Those who perceive themselves as the most stressed have shorter telomeres than those who see themselves as the least frazzled.

"What we do know is that in terms of cohorts, of groups of people, telomere length has some predictive power," says cell gerontologist Thomas Von Zglnicki, professor of cell gerontology in the Institute for Aging and Health in Newcastle. He adds: "If we look at an individual and try to use telomere length as a predictor of anything it's as good as a throwing the dice."

Whis is why, the companies say, they—like cholesterol testers—are not in the business of predictions. Rather, they are exploring the probability of risk.

Monitoring ourselves

How might these shortening telomeres manifest themselves in our sagging jowls, wrinkled skin and gray hair?

Once a cell has divided to the point where its telomeres have been worn to a nub, it enters an arrested state called senescense, or it dies. Senescent cells emit all kinds of pro-inflammatory substances into the tissue and bloodstream. Some scientists believe that it is those toxins that chew away at the collagen and elastin—protein fibers that hold together our organs (including our skin), leading to the "unsightly ripening," as Shakespeare would have it, that we witness in the mirror as we age.