Tooth enamel proteins provide a window into ancient and modern human well-being

A new way to observe tooth enamel could give scientists a better understanding of the health of human populations from ancient times to the present day.

The method, published this week in the Journal of Archaeological Sciencesexamines two immune proteins found embedded in human tooth enamel: immunoglobulin G, an antibody that fights infection, 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 lead author of the study. “Analyzing immune proteins in enamel has never been done before, and this opens the door to studying past diseases and health in a more targeted way than is possible today.”

The study began when Buonasera was a research associate at the University of California, Davis. She and her collaborators, including representatives from local indigenous tribes, tested the presence and amount of proteins in the tooth enamel of three groups of people:

• The Ohlone ancestors lived in a mission outpost dating back to the late 1700s and early 1800s in the San Francisco Bay Area. Their skeletons were inadvertently discovered during a construction project in the area in 2016. The tribe’s descendants gave permission for their teeth to be used in the study.
• European settlers from the late 1800s buried in a San Francisco city cemetery.
• Today’s military cadets who donated their wisdom teeth.

The research team then compared the levels of the two proteins with the known history and experiences of each population. The indigenous peoples of the California mission system experienced high mortality rates, intense stress and the introduction of infectious diseases.

The 19th-century European settlers had shorter life expectancies than modern populations, but as a group they are thought to have experienced less stress and disease than the Ohlone group. Modern military cadets are thought to have enjoyed better health and nutrition than either archaeological group.

The researchers found a strong correlation between high levels of stress and disease in the indigenous population and high levels of these two proteins in their teeth. The protein levels were much higher than those in the other two groups tested.

“Some individuals, particularly children, have very high levels of immunoglobulins, which the body uses to fight disease, and C-reactive protein, which people produce when they’re stressed,” said Jelmer Eerkens, a professor of anthropology at the University of California, Davis, and one of the study’s corresponding authors. “It’s heartbreaking to think about children who may have lost their parents and family to illness, who were thrown into a new cultural environment that they didn’t understand, and the impact that had on their well-being.”

Buonasera said this new way of looking at teeth could allow scientists to gain more detailed insight into historical and prehistoric human experiences, for several reasons.

The first is that teeth form at different periods of human development, from birth to late adolescence or early adulthood. This growth over time of each tooth is analogous to the rings of a tree.

“So this 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 may provide more precise information about health than scientists can get from looking at structural changes in bones or teeth. Many diseases don’t leave visible traces on the skeleton, but proteins in teeth can record responses to disease or inflammation.

Finally, tooth enamel tends to degrade much more slowly than other tissues in the body. This means that it is possible to learn from the proteins in ancient humans’ teeth, providing a timeline of human well-being that goes back thousands of years.

Beyond providing new insights into the lives of ancient humans, the method has the potential to fuel discoveries about the effects of stress, disease and lifestyle on modern humans as well, she said.

“Without wanting to overstate things, studying stresses and immune responses in past populations could provide points of comparison with modern lifestyles that can be particularly valuable because you have this depth of time,” Buonasera said.

In addition to being the first to examine serum proteins trapped in enamel, the study is also innovative because of the precision provided by the new method, said Glendon Parker, an adjunct associate professor at UC Davis and one of the paper’s co-authors.

“We believe that the approach taken by Tammy and her team is relevant in many contexts, for this question and others,” Parker said. “These new tools will give us deeper insights into the lives of peoples in the past. It’s an exciting time for bioanthropology that such tools are available.”