World's oldest person, Ethel Caterham, celebrates 116th birthday in Surrey, England

British great-grandmother Ethel Caterham celebrated her 116th birthday on August 21.

Ms Caterham officially became the oldest living person earlier this year, following the death of a Brazilian nun who previously held the record.

Born in Hampshire in 1909, she currently lives in a care home in Surrey, having outlived her husband and both her daughters.

Naturally, such milestones spark curiosity and admiration.

We have long been fascinated by people who live well past 100, often asking them for their secrets to a long and happy life.

But Ms Caterham's age raises another question: how sure are we that anyone is living to 110, let alone 116?

According to research, a surprising number of the world's so-called "supercentenarians" (people aged 110 and older) may not be quite as old as they claim.

And in many cases, the reason is not some elaborate conspiracy, it is just bad record-keeping.

'Blue Zones' raise red flags

For years, cities like Okinawa in Japan and Sardinia in Italy have been dubbed "Blue Zones", regions where residents reportedly live significantly longer, healthier lives.

But when Dr Saul Newman, a research fellow at the Oxford Institute of Population Ageing, started digging into the demographics behind these zones, things did not quite add up.

Take Okinawa: it is often celebrated as a model of healthy aging, but it actually has one of the lowest life expectancies in Japan, along with high poverty and poor health outcomes.

And yet, it is reportedly full of supercentenarians? Unlikely, says Newman.

He believes the more plausible explanation is a mix of recording errors, misreported birthdates and, in some cases, deliberate misrepresentation.

A similar pattern appears in Sardinia, Italy.

Some of the poorest, least healthy, most crime-ridden parts of Italy have the highest concentration of supercentenarians.

Dr Newman concludes these regions are more likely to produce errors or even pension fraud, where someone may be collecting benefits under the name of a deceased relative.

Birth certificates in the US

In the early 20th century, US states adopted formal birth certificates at different times.

And when a state began requiring accurate, official birth documentation, something fascinating happened: the number of reported supercentenarians dropped dramatically.

Newman found that the introduction of birth certificates led to a 69–82 per cent fall in the number of people reported to have reached age 110.

That suggests that seven to eight out of every 10 so-called supercentenarians may never have reached that age at all.

So where does that leave Ethel Caterham? She may well be 116.

She was born in an era with far better documentation but for many others, reaching 110 may have less to do with a long, healthy life and more to do with a missing birth certificate.

But Ms Caterham shared her own secret to longevity on her birthday last year.

"I listen and I do what I like."