New Scientist - USA (2021-02-20)

46 | New Scientist | 20 February 2021

How old are

you really?

If you want to know how well your body is ageing

you may be in for a surprise, finds Marta Zaraska

W

HEN David Nurse turned 30,

he wanted to find out how his

biological age compared with his

chronological one. A life coach with the US

National Baseball Association, he hoped that

the ultra-healthy lifestyle he advocates to

players had kept his own body young and

healthy, too. So he took a test to assess the

length of his telomeres. It revealed his

biological age to be 28 years. That was in

2017. Two years later, he took another test.
“I was down to 25, so that was great,” he says.
If you google “telomeres”, you are likely
to find them described as an ageing clock.
They are segments of DNA at the ends of
each chromosome that become shorter
every time a cell divides. If this shortening
happens slowly, it suggests that your body is
wearing well. Say you are a 60-year-old with
telomeres as long as those of an average
50-year-old, your mortality risk is equivalent
to that of someone 10 years younger – or so the
story goes. Increasing numbers of people want
this information, and many companies offer
tests like the one Nurse took, together with
various pills claimed to lengthen your
telomeres and, in turn, your lifespan.
If only it were that simple. We are now
discovering that telomeres are an unreliable
ageing clock, which raises questions about the
validity of ageing tests based on them. The
links between telomere length and lifestyle
choices also aren’t as straightforward as we
once thought. In fact, long telomeres can
even be bad news. Nevertheless, there are
some surprising ways we can look after
our telomeres.

At first glance, telomere-mania seems

grounded in science. In 1982, Elizabeth

Blackburn at the University of California,

Berkeley, and Jack Szostak at Harvard

Medical School cracked the riddle of how

chromosomes remain intact when cells divide:

they have repeating units of DNA at their ends

that stop them from unravelling. The pair

called these “telomeres”. Later, they discovered

that each time a cell divides, its telomeres

become shorter, like the ticking of a biological

clock. Meanwhile, Blackburn and Carol Greider

at Cold Spring Harbor Laboratory in New York

identified an enzyme, telomerase, that

promotes the construction of telomere DNA.

These discoveries won Blackburn, Greider

and Szostak a Nobel prize in 2009. Hype soon

followed and researchers began piling into the

field. However, as we find out more about

telomeres, the mythology that has built up

around them is starting to crumble.

For a start, it turns out that having long

telomeres isn’t necessarily a sign that you

have done a great job keeping your body

younger and healthier than other people

of your chronological age. A lot of the

differences between people are down to

genes. We now know that telomere length is

highly heritable, with as much as 60 per cent

of the variation between individuals being

due to their genes. There are several genes

associated with telomere length, and some

of them are responsible for regulating the

activity of telomerase.

What happens to a fetus while in the uterus

also has a huge effect. Studies have linked

shorter telomeres to prenatal exposure to MA

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