Telomere length predicts lifespan

10 January 2012 by Tom Marshall

You can predict how long a young bird is likely to live by looking at just one specialised piece of genetic material in its cells, new research shows.

Zebra finches

Zebra finches

These portions of DNA, called telomeres, occur in almost all higher animals and plants. They mark the chromosome ends and protect organisms' genes from damage.

But they gradually shorten over time, and when they reach a certain point they can no longer do their job, exposing the unprotected chromosomes to damage. This causes cells to malfunction and tissues to deteriorate, hastening death.

Researchers from the Universities of Glasgow and Exeter measured telomere length in a captive population of zebra finches when they were 25 days old, and then at regular intervals throughout their natural lives. The birds' lifespans varied greatly, from just 210 days to almost nine years. Those that started with long telomeres tended to have long lives.

"While there was a lot of variation amongst individuals in telomere length, those birds that lived longest had the longest telomeres at every measurement point," comments Dr Britt Heidinger, the first author of the paper, which is published in Proceedings of the National Academy of Sciences.

It's known that there's some inherited genetic component to telomere length, but also that it varies due to environmental factors such as stress.

Previous research has already shown that telomere length could help predict lifespan in other species, including Alpine swifts and southern giant petrels. But these studies measured the subjects' telomere length only once or twice, and didn't monitor the same individuals throughout their natural lives. So in such studies there are biases that could have been affecting the results.

For example, the petrel research started out with adult birds at a range of ages. This means that those individuals dying young were excluded from the study, and it was not possible to examine early life telomere length.

"What's unique here is that rather than sampling individuals over a range of ages we measured telomere length in these zebra finches from early in life and then followed the same individuals for the rest of their natural lives," says Professor Pat Monaghan of the University of Glasgow, who led the group. "This means that we can show that telomere length in early life is a better predictor of lifespan than telomere length in adulthood."

"There's been a great deal of research on the mechanics of how telomere length changes can cause cells to malfunction; our study provides conclusive evidence that in this is linked to animal lifespans," she adds.

Of course, in the wild birds die for all kinds of reasons that have nothing to do with how long their telomeres are, including disease and predators. The captive finch flock didn't face these perils, so the effect of differences in telomere length was easier to discern. "We're really looking at the capacity for long life in the absence of external factors that cause death," Monaghan explains.

Telomeres are specialised sections of genetic material that sit at the end of chromosomes, marking the chromosome ends and protecting them from gradual damage and from losing genetic information during cell division.

But they have a finite lifespan. Whenever each cell divides, the telomeres protecting its chromosomes get shorter. Eventually, they can't shorten any further and the cell can no longer function properly and stops dividing. So you can imagine how starting off with longer telomeres would keep your chromosomes protected for longer. Long telomeres might also be related to other factors that promote longevity, such as resistance to oxidative damage.

Monaghan says her team is now embarking on a five-year follow-up project to find out how far telomere length is passed on from parents to offspring and how changes in telomere length are affected by environmental factors.

It's certainly too early to know how far telomere length in early life affects human lifespan, Monaghan adds. There have been studies on this, but because humans live so long they've tended to start off with people who are already elderly. So as with her team's previous studies on other birds, it's not impossible that this is biasing the results by excluding individuals who died at younger ages, making it harder to detect the true relationship between lifespan and telomere length.