The death of the world’s oldest person, Maria Branyas Morera, at age 117 may prompt many to ponder the secrets of an exceptionally long life. But scientists say it might be better not to take advice on longevity from centenarians themselves.

According to the Guinness Book of World Records website, Branyas believed her longevity was due to “order, calm, good connections with family and friends, contact with nature, emotional stability, no worries, no regrets, lots of positivity, and distancing herself from toxic people.”

However, Richard Faragher, professor of biogerontology at the University of Brighton, said that in reality science is still trying to figure out why some people live beyond the age of 100.

Faragher said there were two main theories that were not mutually exclusive.

First, he said, some people are basically just lucky. In other words, just because centenarians had certain habits didn’t mean those habits affected their longevity – a logical error known as survivorship bias.

“Just because you survived smoking 60 cigarettes a day doesn’t mean it’s good for you to smoke 60 cigarettes a day,” Faragher said.

The second theory, he said, is that centenarians possess certain genetic traits that allow them to live longer—in other words, their genes make them more robust.

However, Faragher said both theories lead to the same warning: “Never take health and lifestyle advice from a centenarian.”

He added: “What is striking about most centenarians – and these are generalisations – is that they do not exercise much. Very often they have a rather unhealthy diet,” noting that some centenarians are also smokers.

“This contradicts the large body of epidemiological evidence we have on how to extend life expectancy through healthy lifestyles,” he said, adding that a large study found that not smoking, physical activity, moderate alcohol consumption and eating five portions of fruit and vegetables a day could increase life expectancy by up to 14 years.

“The fact that (centenarians) do a lot of these unhealthy things and still get through (life) easily shows that they are either lucky or very well-endowed (genetically) in general,” he said.

Branyas admitted that luck played a role in her long life, while her daughter Rosa Moret once put it down to genetics. “She has never been to hospital, she has never broken bones, she is fine, she is not in pain,” Moret told Catalan regional television in 2023.

Faragher added that many of the reasons discussed for centenarians’ longer life expectancy may actually be examples of reverse causality. For example, the idea that a positive mental attitude can help people live very long may be due, at least in part, to people being more optimistic because of their better health.

“When was the last time you had a really positive mental attitude and a toothache?” he said.

Faragher added that one problem is that when you look at centenarians, you tend to focus on things that might have helped them survive. “But we don’t take into account the factors that prevented them from doing so,” he said.

Prof David Gems, a geneticist at University College London, said that while gender is an important factor in life expectancy – women age more slowly than men – he also agreed that luck plays an important role. One example of this is the natural variability in the rate of ageing.

“I’m working on nematodes that only live for a few weeks,” he said. “The worms are genetically identical and are kept under identical conditions, but the first worms die of old age after about 10 days and the last after about 30 days.”

While at an individual level, a certain amount of luck might explain why some people live beyond the age of 100, experts say there are also known factors that can improve life expectancy at a population level, such as improvements in health care and hygiene.

“For about 100 years, we have seen a huge increase in life expectancy due to progress in reducing the likelihood of child mortality,” says David Sinclair, executive director of the International Longevity Centre, pointing out that this is mainly due to the introduction of vaccinations and clean water.

“What we have seen over the last 20 years and what we will see over the next 20 years is a similar focus on aging,” Sinclair said, adding that this includes improvements in vaccines against flu and shingles, statins and other drugs that would help increase life expectancy in older people.

However, he said governments also need to take action to help individuals make healthier choices – choices that will ultimately help them live longer. He added that many people live in environments where it is difficult to exercise, eat healthily or avoid pollution.

Even if someone reaches three-digit years of age, their life is not necessarily all balloons and glowing birthday cakes.

Sinclair said that while the news about centenarians is often optimistic, it often turns out that these people face challenges, such as living alone for many years.

“The reality is not always as positive as it seems,” he said.