Humans may have finally discovered the secret to a long life, which is hiding in our guts.

Scientists from the University of Copenhagen studied 176 healthy Japanese centenarians - a rare population who reach 100 years or more - and found they all had a mix of bacteria and viruses in their gastrointestinal (GI) tract.

The study showed that specific viruses in the intestines can benefit the microbiome in the gut and, therefore, our health.

While it is impossible to change people's genetic predispositions, the researchers speculate they could change someone's intestinal biome to include the unique mix.

Joachim Johansen, author of the study, said: 'We are always eager to find out why some people live extremely long lives. 

'Previous research has shown that the intestinal bacteria of old Japanese citizens produce brand new molecules that make them resistant to pathogenic — that is, disease-promoting — microorganisms. 

'And if their intestines are better protected against infection, well, then that is probably one of the things that cause them to live longer than others.'

The team developed an algorithm to map the centenarians' intestinal bacteria and bacterial viruses.

These results were then compared to a group of adults between the ages of 18 and 60. 

Mr Johansen said the team found 'great biological diversity in both bacteria and bacterial viruses' in the centenarians.