A new way of looking at tooth enamel could give scientists a path toward a deeper understanding of the health of human populations, from ancient to modern times.
The method, published this week in the journal Journal of Archaeological Scienceexamines two immune proteins found embedded in human tooth enamel: immunoglobulin G, an antibody that fights infections, and C-reactive protein, which is present during inflammation in the body.
“These proteins are present in tooth enamel, and we can use them to study the biological and potentially emotional health of past human populations,” said Tammy Buonasera, an assistant professor at the University of Alaska Fairbanks and senior author on the paper. “Analysis of immune proteins in enamel has not been done before, and this opens the door to studying disease and health in the past in a more targeted way than we can do today.”
The study began when Buonasera was a research associate at the University of California, Davis. She and her collaborators, who included representatives of local indigenous tribes, analyzed the presence and amount of proteins in the tooth enamel of three groups of people:
- Ancestors of the Ohlone people from a mission outpost dating to the late 18th and early 19th centuries in the San Francisco Bay Area. Their skeletons were inadvertently discovered during a construction project in the area in 2016. Descendants of the tribe gave permission for their teeth to be used in the study.
- Late 19th century European settlers buried in a San Francisco city cemetery.
- Modern-day military cadets who donated wisdom teeth.
The research team compared the levels of the two proteins to the known history and experiences of each of the populations. Indigenous peoples in the California mission system experienced high mortality rates, intense stress, and introduced infectious diseases. European settlers in the 19th century had shorter life expectancies than present-day populations, but as a group were presumed to have experienced lower degrees of stress and disease than the Ohlone group. Present-day military cadets were presumed to have enjoyed better health and nutrition than both archaeological groups.
The researchers found a close correspondence between evidence of high levels of stress and disease in the indigenous population and high levels of the two proteins in their teeth. The protein levels were much higher than in the other two groups analysed.
“We see certain people, especially children, with very high levels of immunoglobulins, which the body uses to fight off disease, and C-reactive protein, which people produce when they’re under stress,” said Jelmer Eerkens, a professor of anthropology at the University of California, Davis and one of the paper’s corresponding authors. “It’s heartbreaking to think about children who may have lost parents and family members to illness, who were thrown into a new cultural environment they didn’t understand, and how this affected their well-being.”
Buonasera said this new way of looking at teeth could allow scientists a more detailed look at historical and prehistoric human experiences, for several reasons.
The first is that teeth form at different stages of human development, from the womb to late adolescence or early adulthood. This growth of each tooth over time is analogous to the rings of a tree.
“So it has the potential to give us a record, from birth to early adulthood, of a person’s health status,” Buonasera said.
Second, immune proteins in tooth enamel could provide more specific information about health than scientists can glean from looking at structural changes in bones or teeth. Many diseases leave no visible trace in the skeleton, while tooth proteins can record responses to disease or inflammation.
Finally, tooth enamel tends to degrade much more slowly than other tissues in the body. That means there is the potential to learn from the proteins in the teeth of ancient humans, which would offer a timeline of human well-being stretching back thousands of years.
In addition to gaining new insights into the lives of ancient humans, the method has the potential to also drive discoveries about the effects of stress, disease and lifestyle on modern humans, he said.
“Without trying to overstate things, looking at stress and immune responses in past populations could provide points of comparison to modern lifestyles that can be especially valuable because you have that depth of time,” Buonasera said.
In addition to being the first to examine serum proteins trapped in enamel, the study is also groundbreaking because of the precision the new method provides, said Glendon Parker, an adjunct associate professor at UC Davis and one of the paper’s co-authors.
“We think the approach Tammy and her team have taken is relevant in many contexts, for this and other questions,” Parker said. “These new tools will give us greater insight into the lives of people in the past. It’s an exciting time for bioanthropology as these tools become available.”