Research has long established that the first 1,000 days after conception (about 280 days until birth and then up to 24 months of age) significantly influence a person’s overall life expectancy and risk for chronic diseases.
In general, low birth weight has been the primary indicator of early life stress, but this can only measure stress or maternal nutrition up until birth and still falls quite short of a measurement useful for the first 1,000 days.
Now, a new study at the University of Washington (UW) suggests that an asymmetric lower face is an accurate marker of early life stress occurring after birth.
“Asymmetries in the skull and teeth have been used for decades by anthropologists to mark environmental stress, but they have only rarely been used in living populations,” said study author Philippe Hujoel, an adjunct professor of epidemiology in the School of Public Health and professor in the School of Dentistry.
“Such lower-face asymmetries can be assessed by looking at the dental bite in the permanent teeth — an exam that can be completed in seconds and with more certainty than a mother’s recall of birth weight and more ease than a search for a birth certificate.”
A crooked, or asymmetric, bite is described by Hujoel as the teeth biting backward or forward on one side of the face but normally on the other side.
Backward-biting asymmetries, the most common lower-face asymmetry in the U.S. population, fluctuate randomly between the left and right sides of the face. Such randomness is evidence for early life stress, he said.
Hujoel emphasized that crooked teeth, overbites, and underbites are different than an asymmetric bite. Those conditions can be associated with asymmetric and symmetric bites, the latter of which is largely a reflection of genetics, not environmental stress, he said.
For the study, Hujoel and researchers Erin Masterson and Anne-Marie Bollen analyzed data from 1966 to 1970, which involved a sample of 6,654 adolescents (aged 12 to 17) who were participating in a National Health Examination Survey.
The team had to look back four decades for data because in the 1970’s, he said, dental researchers in charge of designing U.S. surveys began to disregard the value of diagnosing facial asymmetry, and stopped taking those measurements.
“From a biological perspective, this decision resulted in an inability to reliably track trends in the U.S.,” said Hujoel. “We don’t have current information on the prevalence of lower-face asymmetries in the U.S. population.”
The researchers found that one in four of the U.S. adolescents had lower-face asymmetries.
“Lower-face asymmetries were common in a generation that became typified by an epidemic of diabetes and obesity in adulthood,” said Hujoel.
More research is needed to determine whether lower-face asymmetries are predictive of chronic diseases in living populations in the same way that skull asymmetries have been associated with degenerative diseases in long-deceased populations.