Bacteria found in people's spit does not vary much around the world, a surprising finding that could provide insights into how diet and cultural factors affect human health, researchers said on Thursday.

Because the human body harbors 10 times more bacterial cells than human cells, scientists are trying to understand more about the bacteria we carry.

The human mouth is a major gateway for bacteria into the body and it contains a diverse array of microbial species. Yet scientists know little about this diversity and how it relates to diet, environment, health and disease, they added.

"We are interested in this because by studying the bacteria we can get more insights into human populations than we would get from just studying the human DNA," Mark Stoneking of the Max Planck Institute in Leipzig, Germany, who led the study, said in a telephone interview.

In their study published in Genome Research, the team sequenced bacteria found in saliva samples taken from 120 healthy volunteers from North America, South America, Western Europe, Eastern Europe, Africa and Asia.

Not surprisingly, they observed considerable diversity of bacterial life in the overall saliva microbiome, both within and between individuals.

But when comparing samples from different geographic areas they found not much variation, suggesting that bacteria within the mouth of a person's neighbor is likely to be just as different as someone on the other side of the world.

The findings could help better understand human migrations and populations as well as providing background for future studies looking at the influence of diet, cultural factors and disease on differences in saliva bacteria.

"The saliva microbiome does not vary substantially around the world," Stoneking said in a statement. "Which seems surprising given the large diversity in diet and other cultural factors that could influence the human salivary microbiome."