The length of telomeres, which appear at the end of human chromosomes, may help scientists determine a person’s longevity. (Peter Lansdorp)

As early as this fall, we may be able to get a simple blood test that can help us monitor not only our general health status but also how fast we’re aging — or at least how fast our cells are aging.

The test will measure the length of our telomeres, the caps on the ends of chromosomes that keep our DNA intact and our cells thriving.

News about the test’s imminent release has spurred a flurry of misleading reports suggesting that we’re on the cusp of being able to learn how long we’ll live — and whether we can ward off the irksome outward signs of aging. While scientists are divided over the value of the test for individuals, no serious researchers are saying a telomere test will be some kind of crystal ball.

At best, the new test represents another, more powerful tool among the tests already used to assess health — cholesterol, triglyceride and glucose measurements — not an entirely new approach. They 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.

The ‘core pathway’

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 has led many scientists to view telomere length as a marker of biological aging, a molecular clock ticking off the cell’s life span, as well as an indicator of overall health. In general, older people have shorter telomeres than younger ones.

Ronald A. DePinho, a cancer biologist at Boston’s Dana-Farber Cancer Institute, recently proposed a unified theory of aging, with malfunctioning telomeres as what he called 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 the probability of disease and early mortality. It is not a diagnosis,” stresses Elissa Epel, a health psychologist at the University of California at San Francisco and a founder of Telomere Health Inc., one of the companies making the test. “Telomere length is only helpful information when interpreted correctly, which is probabilistically.”

Here’s how that interpretation would work: Like other medical tests based on risk assessments — such as a measure of cholesterol levels — the companies aim to compare your telomere length to a norm determined through statistical analysis of people similar in age, sex and behaviors. Both THI, based in Menlo Park, Calif., and Life Length S.L., in Madrid, are conducting those studies now.

As molecular biologist Calvin B. Harley, chief scientific officer 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.”

‘As good as throwing the dice’

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 co-founder of THI, and Carol Greider, a molecular biologist at the Johns Hopkins School of Medicine — disagree about the value of a test.

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 wrote in an e-mail.

There’s a growing body of research showing correlations between telomere length, particularly in white blood cells, and lifestyle. For example, studies show that those who exercise regularly have longer telomeres than couch potatoes. Those who perceive themselves as the most stressed have shorter telomeres than those who see themselves as the least frazzled. And as Blackburn noted, certain diseases, too, correlate with shorter telomeres.

“What we do know is that in terms of cohorts, of groups of people, telomere length has some predictive power,” says Thomas von Zglinicki, a professor of cell gerontology at Britain’s Institute for Ageing and Health in Newcastle. But, he adds: “If we look at an individual and try to use telomere length as a predictor of anything, it’s as good as throwing the dice.”

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

Look in the mirror

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.

The good news is that research also has shown that telomeres can lengthen over time, possibly through such lifestyle changes as an increase in the intake of omega-3 fatty acids, reduction of stress and belly fat, exercise, meditation and other interventions.

A recent paper showed that people who went on an intensive meditation retreat had higher levels of the restorative enzyme telomerase — which can add to existing telomeres — than those who did not go. Another study showed that over a period of five years, telomeres lengthened in those with the highest levels of omega-3 fatty acids in their blood.

“It’s early in the research to make any definitive statements,” says Epel, “but the greatest benefit” for the individual who takes the tests when they become available, “will probably come from personal relative measurements; that is, how your telomere length changes over time — say, at baseline and then after six months, when certain lifestyle behaviors have been changed. This is about health maintenance, not detecting disease.”

“People need feedback on whether their efforts are working,” she says. “Monitoring telomere length may be a helpful way to promote the paradigm shift toward prevention of disease.”

Singer is the author of Stress Less (Hudson St. Press), an investigation of telomeres, stress and aging.