Ancient teeth found in Thailand show that the practice of chewing on betel nuts emerged at least 4,000 years ago during the Bronze Age.

Betel nuts are the fruit of the areca palm tree. The areca palm is native to the Philippines but was dispersed widely throughout the region by ancient human migrants.

Chewing betel nuts and leaves has been a common practice for local people in the tropics – particularly South and Southeast Asia – for thousands of years. The nut acts as a stimulant drug, enhancing alertness, energy, euphoria and relaxation.

Sometimes the nut is mixed with leaves and other ingredients to form a “betel quid”.

The practice of chewing betel nuts has declined in recent times. Not only can it lead to stained reddish-brown or even black teeth, there is evidence that it is linked to long-term health problems like addiction, gum disease, oral cancer (particularly when used with tobacco) and heart disease.

Archaeologists have now identified the earliest evidence of betel nut chewing in the world.

The discovery of 4,000-year-old dental plaque with trace compounds from betel nuts is detailed in a paper published in Frontiers in Environmental Archaeology.

“We identified plant derivatives in dental calculus from a 4,000-year-old burial at Nong Ratchawat, Thailand,” says first author Piyawit Moonkham, an anthropological archaeologist at Thailand’s Chiang Mai University. “This is the earliest direct biomolecular evidence of betel nut use in Southeast Asia.”

“We demonstrate that dental calculus can preserve chemical signatures of psychoactive plant use for millennia, even when conventional archaeological evidence is completely absent,” adds senior author Shannon Tushingham, from California Academy of Sciences, USA. “In essence, we’ve developed a way to make the invisible visible – revealing behaviours and practices that have been lost to time for 4,000 years.”

Archaeological burials with associated artifacts at Nong Ratchawat. Credit: Piyawit Moonkham.

The team identified the betel nut compounds from 36 hardened tooth plaque samples found in ancient human burials in Thailand.

They confirmed the presence of betel nut compounds by producing their own betel quid samples.

“We used dried betel nut, pink limestone paste, Piper betel leaves and sometimes Senegalia catechu bark and tobacco. We ground the ingredients with human saliva to replicate authentic chewing conditions,” Moonkham explains.

“Sourcing materials and experimentally ‘chewing’ betel nuts to create authentic quid samples was both a fun and interesting process.”

Results showed that 3 samples, all from the same female individual, contained traces of arecoline and arecaidine – organic compounds found in betel nuts.

“The presence of betel nut compounds in dental calculus does suggest repeated consumption, as these residues become incorporated into mineralised plaque deposits over time through regular exposure,” says Tushingham.

Product of “chewing” betel quid. Credit: Piyawit Moonkham.

Strangely, the ancient individual’s teeth showed no signs of staining from betel nut chewing.

The team say this could be the result of different consumption methods, teeth cleaning practices or processes which affected the preservation of stains in the thousands of years since the individual died.

Despite betel compounds being found in samples from only one individual, there is no evidence that this person received special treatment or was of a different social status.

“Dental calculus analysis can reveal behaviours that leave no traditional archaeological traces, potentially revolutionising our understanding of ancient lifeways and human-plant relationships,” Tushingham says. “It could open new windows into the deep history of human cultural practices.”

“Understanding the cultural context of traditional plant use is a larger theme we want to amplify – psychoactive, medicinal and ceremonial plants are often dismissed as drugs, but they represent millennia of cultural knowledge, spiritual practice, and community identity,” Moonkham adds. “Archaeological evidence can inform contemporary discussions by honouring the deep cultural heritage behind these practices.”