In a quiet rice field in central Thailand, archaeologists have uncovered an unlikely time capsule: ancient dental plaque from a Bronze Age woman that holds the earliest direct evidence of betel nut chewing in Southeast Asia. Using biomolecular analysis, researchers found residues of psychoactive compounds preserved for 4,000 years in the calcified plaque on her teeth.
This finding, published in Frontiers in Environmental Archaeology, pushes back the timeline for betel nut use and reveals new ways to detect ancient plant-based cultural practices that leave no visible trace.
Making the Invisible Visible
At the Nong Ratchawat site, where more than 150 human burials have been excavated since 2003, scientists analyzed dental calculus (hardened plaque) from six individuals. Only one, Burial 11, yielded a surprising result: chemical signatures of arecoline and arecaidine, compounds found in betel nuts that produce stimulant effects like heightened alertness and euphoria.
“We identified plant derivatives in dental calculus from a 4,000-year-old burial at Nong Ratchawat, Thailand,” said Dr. Piyawit Moonkham of Chiang Mai University. “This is the earliest direct biomolecular evidence of betel nut use in southeast Asia.”
Senior author Dr. Shannon Tushingham of the California Academy of Sciences added, “We’ve developed a way to make the invisible visible, revealing behaviors and practices that have been lost to time for 4,000 years.”
What They Found, and How
- 36 dental calculus samples were tested from six individuals
- Only Burial 11 (a likely female) showed biomolecular evidence of betel nut use
- Key compounds detected: arecoline and a possible derivative of arecaidine
- No visible staining of teeth was present
- Experimental “chewed” betel quids were used as controls to validate the method
To simulate authentic chewing conditions, the team prepared quids using betel nut, Piper betel leaves, pink limestone paste, and sometimes tobacco and Senegalia catechu bark, all mixed with human saliva. These controls helped confirm that the compounds found in Burial 11’s teeth were indeed from betel nut.
Culture in a Plaque Sample
The presence of betel nut compounds suggests habitual use. Yet the woman’s teeth lacked the dark reddish-black staining commonly associated with betel chewing. This could be due to different chewing techniques, oral hygiene, or the ravages of time on soft tissues and tooth enamel.
Although Burial 11 included some grave goods, such as stone beads and clay vessels, the researchers found no evidence that she held a unique social or ceremonial role. Still, her biochemistry tells a story invisible to the naked eye, one that likely reflects a broader cultural tradition.
A New Tool for Ancient Habits
Dental calculus is fast becoming a powerful lens through which archaeologists can detect ancient behaviors that leave no trace in artifacts or visible remains. Previous evidence of betel nut use relied on stained teeth or scattered plant remains. This study goes further.
“Dental calculus analysis can reveal behaviors that leave no traditional archaeological traces,” said Tushingham. “It could open new windows into the deep history of human cultural practices.”
Moonkham emphasized the cultural context: “Psychoactive, medicinal, and ceremonial plants are often dismissed as drugs, but they represent millennia of cultural knowledge, spiritual practice, and community identity.”
Why It Matters
Despite modernization efforts and changing attitudes, betel nut chewing still survives in rural and minority communities in Thailand and Southeast Asia. Its cultural resonance persists in rituals, social customs, and oral traditions. This research not only reframes how archaeologists study psychoactive plant use but also helps reclaim overlooked aspects of human history.
As more calculus samples are studied from the 150+ burials at Nong Ratchawat and elsewhere, new patterns may emerge about gender, status, and the social functions of ancient chewing habits. For now, one Bronze Age woman’s teeth have helped make visible a hidden chapter of Southeast Asian culture.
Journal Reference
Journal: Frontiers in Environmental Archaeology
DOI: 10.3389/fearc.2025.1622935
Article Title: Earliest Direct Evidence of Bronze Age Betel Nut Use: Biomolecular Analysis of Dental Calculus from Nong Ratchawat, Thailand
Publication Date: July 31, 2025
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