Diachronic changes in linear enamel hypoplasia during the Edo period (1603-1867), Japan

摘要

Linear enamel hypoplasia (LEH) is a useful indicator of childhood health. This study aimed at investigating whether there was any diachronic change in LEH occurrence during the Edo period (1603-1867). The Edo period, which experienced no major transition in subsistence and had no large-scale contact with foreign population, did undergo various social changes that could have affected childhood health status. The skeletal remains of 144 adult individuals recovered from seven burial sites in Tokyo were examined. Based on historical records and archaeological evidence, these individuals were divided into two time-period groups, the early Edo period and the late Edo period. Each group was then subdivided into the two age-at-death groups of young and old. The late Edo period groups were also divided into coffin-type groups, which reflect their social status. Comparison of general prevalence, frequency distribution, and the mean number of LEHs observed per tooth revealed that the individuals of the late Edo period groups of any coffin type tend to have fewer LEHs than those of the early Edo period groups, and significant differences were found either in the frequency distribution or in the mean number of LEHs per tooth. Considering the possible factors that could affect the result, such as age-at death distribution and social status, the observed difference between the time periods can be attributed to diachronic change, which is assumed to be due to improvements in childhood health status during the Edo period. This assumption is compatible with historical evidence suggesting that the living environment in the city of Edo was improving in the 17th century and stabilized in the 18th century as a result of the establishment of basic infrastructure and improvements in public safety. The findings of this study will help us understand childhood health status in a changing society.