National Geographic News
A photo of a male skeleton

This young male was buried wearing bead jewelry at an ancient cemetery in Sudan.

Photograph by Donatella Usai, Centro Studi Sudanesi and Sub-Sahariani (CSSeS)

Traci Watson

for National Geographic

Published July 16, 2014

The purple nutsedge is one of the world's worst weeds, spreading stealthily underground and shrugging off herbicides as if they were soda water. But new research shows that for one ancient people, this noxious plant may have served as a tooth cleaner.

A new analysis of skeletons reveals that people who lived in Sudan 2,000 years ago were eating the purple nutsedge. Those people had surprisingly sound teeth—and the antibacterial properties of the weed may deserve the credit, scientists say in a study published in the journal PLOS ONE on Wednesday.

Early humans generally had relatively few cavities, thanks in part to meals that were heavy on the meat, light on the carbs.

Then humans invented farming and began eating more grain. Bacteria in the human mouth flourished, pouring out acids that eat away at the teeth. The first farmers tended to have much more tooth decay than hunter-gatherers did.

But when scientists looked at the teeth of people buried roughly 2,000 years ago in an ancient cemetery called Al Khiday 2, they found that fewer than one percent of the teeth had cavities, abscesses, or other signs of tooth decay, though those people were probably farmers, says study co-author Donatella Usai of Italy's Center for Sudanese and Sub-Saharan Studies.

A photo of purple nutsedge.
Extracts of purple nutsedge (above) impede the growth of the bacteria most widely implicated in tooth decay.
Photograph by Dinodia Photos, Alamy

Analysis of hardened bits of plaque on the teeth showed those interred at the cemetery had ingested the tubers of the purple nutsedge, perhaps as food, perhaps as medicine. People buried at Al Khiday at least 8,700 years ago—before the rise of farming there—also consumed the tubers, probably as food.

Experiments by other researchers show that extracts of the weed impede the growth of the bacteria most widely implicated in tooth decay. So the weed could have served as both a nutritious dinner and a primitive, if unintentional, antibacterial potion, the scientists say, though they caution that they haven't proved a link.

Such a function is certainly possible, says biological anthropologist Sarah Lacy of the University of Missouri-St. Louis, who is not associated with the new study. No other example has been reported of a specific plant that kept tooth decay in check among ancient people, says Lacy, who calls the results "very exciting."

The purple nutsedge tuber may have many virtues, but a nice flavor isn't one of them. People might have tried to tame the tubers' bitterness by cooking them, says study co-author Karen Hardy of the Catalan Institution for Research and Advanced Studies at the Autonomous University of Barcelona, or they may have just tolerated the bad taste.

"They might have been using it for some medicinal purpose," Hardy says. "Medicine always tastes horrible, so it would be par for the course."

F Gerard Lelieveld
F Gerard Lelieveld

Why don't we eat it then? I brush, I floss, I pick, I waterpick, I eat less sugar, but still my teeth form cavities.

gunapal kathiresan
gunapal kathiresan

 Street dog near my home use to eat this plant whenever they feel sick and when there food not getting digest.  I never seen some one used to clean teeth. 

Pierre-François PUECH
Pierre-François PUECH

A very old medicine from ancient Egypt that does not tastes horrible.       Cyperus esculentuswhose small tubercles are eaten nowadays were also eaten by ancient Egyptians. Cyperus esculentus and Cyperus papyrus (the lower part of the plant was chewed uncooked for its sugar taste or baked in a pan, stems were also crushed for flour) have a high percentage of fibers charged with phytolithes (mineral plant inclusions) with polishing properties that produce a characteristic blunt appearance of dental wear. The use of Cyperus as masticatories develops the flow of saliva which increases the deposit of calculus, but dental wear reduces the number of carious cavities. Pierre-François PUECH

Gia Williams
Gia Williams

@F Gerard Lelieveld if you a a lot of dental treatment as a child then its should be about maintenance of this care. cutting back on sugar and drinking water after eating is best. But if you are still getting caries in your mouth there maybe an underlying factor in your diet, such as grazing on food and changing you PH levels in your mouth. 

Tom Carberry
Tom Carberry

@Pierre-François PUECH A lot of Egyptian mummies had terrible teeth and some show evidence of death from abscesses.  This probably happened because the Egyptians ate a diet heavy in bread made from flour that contained a lot of sand.  The bread encouraged mouth bacteria and the sand eroded the teeth even more.

Gia Williams
Gia Williams

@Tom Carberry @Pierre-François PUECH you are very much right on this fact and people today still ignore signs of abscesses and just want to mask it by taking antibiotics and not dealing with the problem at hand due to lack of funds or fear of dental treatment. There is a massive lack of understanding in the general public in regards to how serious dental decay can be and if you have an underlying heart condition you can put your health at risk and will die if untreated. I have worked in dental for 16 years and watch people put there lives at risk with bad oral hygiene.


Popular Stories

The Future of Food

  • Why Food Matters

    Why Food Matters

    How do we feed nine billion people by 2050, and how do we do so sustainably?

  • Download: Free iPad App

    Download: Free iPad App

    We've made our magazine's best stories about the future of food available in a free iPad app.

See more food news, photos, and videos »