4,000-year-old teeth reveal the oldest evidence of betel nut chewing

What if evidence of a cultural tradition stretching back 4,000 years was hiding in someone’s smile? As it turns out, dental calculus has been concealing traces of an ancient habit – betel nut chewing.

Betel quid is a mixture of areca nut, betel leaves, slaked lime, and sometimes tobacco. It has played a central role in religious ceremonies and social gatherings in Southeast Asia. People also use it in traditional medicines and curative practices. 

Researchers in Thailand have found the earliest evidence of betel nut use. They analyzed chemical traces in ancient dental calculus, which is hardened plaque.

Identifying markers of betel nut chewing

To explore whether this ancient habit could be detected in human remains, researchers used a two-phase approach. First, they tested modern samples of betel leaves and areca nut to detect the key compounds. 

These included hydroxychavicol from the betel leaf, arecoline from betel nut, and nicotine from tobacco (which is sometimes added). Researchers used LC-MS (liquid chromatography-mass spectrometry) to carry out this phase. 

In the second phase, the researchers analyzed 36 samples of ancient dental calculus taken from six human burials at the Nong Ratchawat site in Central Thailand. These burials are about 4,000 years old.

Evidence of betel nut chewing

Researchers identified arecoline and arecaidine derivatives, compounds found in areca nut, in the modern test samples and in three dental calculus samples collected from a female burial. 

This is the first time researchers have identified betel nut residues in dental calculus. This offered a rare molecular glimpse into a 4,000-year-old habit.

The lack of staining on the teeth, an obvious marker of betel nut use, raised interesting questions.

Multiple factors may explain the discrepancy: the person might have drunk the mixture or cleaned the teeth often, the chewing duration or frequency might have been low, or taphonomic processes might have removed the stains.

Following the trail of betel chewers

The researchers aimed to determine whether they could detect chemical traces of betel nut and leaf in the teeth, how uniformly those traces were distributed in the mouth, and whether the habit was common across the population.

Since molars and premolars do most of the chewing, the team expected these teeth to show stronger chemical signals. Hence, they expected that the biomarkers could be detected using LC-MS analysis.

The researchers also hypothesized that all adults, regardless of age, gender, or social status, may have practiced betel nut chewing. The study found chemical traces of areca nut, but none from betel leaf.

In some individuals, tooth decay and gum disease were noticed. Still, researchers did not report any conditions primarily associated with betel nut chewing, such as osteoarthritis of the TMJ (temporomandibular joint) or extreme tooth wear.

Despite this, researchers believed that betel nut chewing could have occurred. Lack of visible clues does not mean it did not happen. It may simply be that the chemical detection methods could not capture it.

Archaeological evidence in Thailand

Long before this biomolecular discovery, archaeologists had uncovered the remains of areca nuts at Thai sites like Spirit Cave and Ban Chiang. This suggests that chewing betel nuts is an ancient tradition.

Later studies confirmed that the practice existed in mainland Southeast Asia, dating from 14,000 to 1,500 years ago.

Researchers previously found indirect archaeological evidence, such as stained teeth and plant fragments, suggesting widespread betel nut use during the prehistoric period, as far back as 14,000 years ago.

Even though rural and minority communities still chew betel nuts, Thai governmental modernization policies since the 1940s have led to their decline. Modern policies emphasize the health risks associated with betel nut chewing.

Dental calculus preserves biomarkers

However, only a few biomolecular studies have directly confirmed betel nut chewing by identifying the associated chemicals, called alkaloids, in the stained teeth. Only recently have researchers begun exploring hardened dental plaque for traces of betel nut. 

New studies have shown that analyzing dental calculus on ancient teeth can reveal information about foodways, nutrition, health, diet, or even milk consumption. It can also provide insights into the use of psychoactive plants and even personalized use patterns.

For instance, researchers previously conducted studies on ancient dental calculus to determine tobacco use in North Americans.

They found that it preserved both chemical and microscopic clues. This suggests dental calculus could help detect other plant-based psychoactive substances, too. 

Future potential for discoveries

By 2020, archaeologists had excavated about 156 burials at the Nong Ratchawat site. Since they have analyzed only six so far, there is significant potential to study dental calculus from the remaining burials. 

Future research will examine how psychoactive plants were used across different ages and genders, and how these practices shaped ancient Thai and Southeast Asian cultures.

Researchers could apply the chemical techniques used here to other ancient sites across Southeast Asia, opening new windows into how the use of psychoactive plants shaped everyday life, rituals, and even social structures.

The full study was published in Frontiers in Environmental Archaeology.

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