An article popped up in my news feed yesterday. The title read: “Skeletal marker of physiological stress might indicate good, rather than poor, health“. The summary of the article stated that archaeologists may be re-assessing whether linear enamel hypoplasia (LEH) may actually be an indicator of good health… We’ll just say I was more than a little suspicious of this popular news outlet and their seemingly sensational title. So I went to the source, the peer-reviewed journal article written by Yaussy, DeWitte, and Redfern (2016) to see what their evidence and conclusions really were.
First, a little background on LEH. Linear enamel hypoplasia manifests as furrows or indentations of decreased enamel on teeth due to interruption during development. They are attributed to times of high metabolic stress, such as periods of malnutrition, but can also be due to trauma or chronic illness. It has been argued to be useful in determining whether individuals were stressed during their childhood, and at what age this stress started and stopped. As you can see in the photo below, these lines of enamel disruption are very clear, and therefore have been quite helpful in understanding childhood stress in the past.
In their study, Yaussy, DeWitte, and Redfern (2016) examine possible famine burials from medieval London in order to develop a better understanding of selective mortality during a crisis; basically, they want to understand who was more likely to die in periods of high stress. Their sample comes from medieval London, which from the 12th through 16th centuries experienced massive population growth, but also a number of crises, including severe famines. When individuals have restricted access to food, they become malnourished and more susceptible to infectious diseases. Who is most susceptible to starvation and disease varies by culture and context, but previous studies have shown that often men, children under 10, and the elderly have elevated risk of mortality.
The sample for their study comes from the St Mary Spital cemetery, located outside London, near the Borough of Tower Hamlets. It was established by a medieval priory and hospital that was founded in 1197 CE to serve the poor and women in childbirth. The cemetery was in use from 1197 to 1539 CE. A total of 10,516 burials were recovered during excavations. Yaussy, DeWitte, and Redfern (2016) specifically examines burials dating from 1349 to 1350, a period defined by both famine and the Black Death, and compare single interment burials (Type A, 713 individuals) against the larger mass graves consisting of multiple layers of the dead stacked upon one another (Type D, 814 individuals). Each individual was assessed for age, sex and evidence of stress, specifically using cribra orbitalia, linear enamel hypoplasia (LEH), and periosteal new bone formation. Prior research has shown that these changes in bone and teeth are associated with malnutrition and elevated risk of mortality.
Results from the analysis showed that there was a higher frequency of periosteal new bone growth in the Type A regular burials, and a higher frequency of LEH in the Type D mass grave burials. Periosteal new bone growth can only occur if an individual survive the stress that is attacking their body, and indicates that they were healthy enough to survive that particular trauma. Yaussy, DeWitte, and Redfern (2016) argue that “individuals in attritional burials [type A] with observable lesions may have been able to survive physiological stressors long enough to develop lesions, while people in the famine burials [type D] without observable lesions were relatively frail and perished before lesions could develop”. Conversely, LEH is a sign of childhood stress and malnutrition, and individuals who had these traumas early on may not have been physically able to face the disease and starvation associated with famine periods. Therefore, LEH is a sign of underlying frailty and susceptibility.
Yaussy, DeWitte, and Redfern (2016) conclude that individuals who experienced early life stress, as evidenced by the presence of LEH, were more frail and susceptible to disease, and thus, more likely to die in periods of famine. However, individuals with periosteal new bone growth are demonstrating evidence of healing, and may indicate their ability to survive during stressful periods. They also found that individuals with LEH died at younger ages than those with periosteal new bone growth, further supporting their argument.
This is a really fascinating study, and I highly suggest reading the whole article to see their other arguments about age and sex variation in mortality. The results are really interesting, and it does bring up something important that we don’t often discuss, the importance of healing. When we see trauma or disease present in a skeleton, it is important to discern whether it was active, and whether it healed at all. While new bone growth is still pathological, it is also a positive sign of healing in many cases and may indicate a healthy individual!
Yaussy SL, DeWitte SN, & Redfern RC (2016). Frailty and famine: Patterns of mortality and physiological stress among victims of famine in medieval London. American journal of physical anthropology PMID: 26854255