Date Published: March 7, 2019
Publisher: Public Library of Science
Author(s): Samantha M. Hens, Kanya Godde, Kristin M. Macak, Christopher D. Lynn.
Portugal underwent significant political, demographic and epidemiological transitions during the 20th century resulting in migration to urban areas with subsequent overcrowding and issues with water sanitation. This study investigates population health during these transitions and interprets results within a framework of recent history and present-day public health information. We investigate skeletal evidence for anemia (cribra orbitalia and porotic hyperostosis) as indicators of stress and frailty–i.e., whether the lesions contribute to susceptibility for disease or increased risk of death.
The presence and severity of skeletal lesions were compared against known sex and cause of death data to investigate potential heterogeneity in frailty and the relationship between lesions and risk of dying over time. Additionally, we tested for the presence of selective mortality in our data (i.e., whether or not the sample is biased for individuals with higher frailty). Our sample derives from a large, documented, modern Portuguese collection from Lisbon and is the first study of its kind using a documented collection. The collection represents primarily middle-class individuals.
Analyses indicated that porotic hyperostosis became more common and severe over time, while cribra orbitalia severity increased over time. Neither process was linked to cause of death. However, there was a significant relationship to sex; males exhibited a higher prevalence and severity of lesions and increased mortality. A Gompertz function showed decreased survivorship in early life but increased survivorship over age 60. Using comorbidities of anemia, we were unable to detect selective mortality–i.e., in our sample, lesions do not represent a sign of poor health or increased frailty and are not significantly linked with a decreased mean age-at-death. However, lesion prevalence and severity do reflect the socioeconomic processes in urban Lisbon during the 1800s and 1900s and the possibility of water-borne parasites as the contributing factor for iron deficiency anemia.
Skeletal samples provide information about the age-at-death, health, and lifestyles of past populations and may be useful in illuminating trends in morbidity and mortality across sociopolitical or socioeconomic transitions throughout history. The 20th century in Portugal was characterized by significant changes to the political-economy resulting in migration into urban centers with subsequent overcrowding and water contamination issues. Thus, an analysis of skeletal indicators of disease (e.g., iron deficiency anemia) coupled with age-at-death data provide an opportunity to investigate whether skeletal lesions are a sign of overall frailty, susceptibility to disease and/or an increased risk of death during this critical period in Portuguese history. However, over twenty-five years ago, the landmark paper, The Osteological Paradox: Problems of Inferring Prehistoric Health from Skeletal Samples , outlined three fundamental problems underlying interpretations of health and disease in past populations. These problems include: (1) demographic nonstationarity, wherein skeletal collections derived from cemetery contexts may reflect populations that were subject to migration or changes in fertility rates; (2) hidden heterogeneity in frailty, wherein individuals exhibit unequal (and ultimately unknown) susceptibility to disease and risk of death due to genetically determined biological differences, differential exposure to disease vectors, or differences in nutritional status owing to behavioral, cultural, or environmental factors; and (3) selective mortality, wherein the skeletal samples represent biased representatives of the living populations from which they are drawn because individuals with the highest frailty at a particular age are more likely to die and enter the skeletal assemblage. While nonstationary populations are a concern for paleodemographers and population-level studies within paleopathology, hidden heterogeneity in risk and selective mortality affect ancient health research more directly . Wood and coworkers  argue that researchers must exercise caution when interpreting skeletal lesions and their link to health. Skeletal lesions have traditionally been viewed as a sign of poor health; however, because some skeletal lesions take considerable time to form, they may actually indicate a healthier individual, one who has survived for an extended length of time , an idea that is essential to Wood and coworkers’  arguments.
The mean age-at-death differed between males (53.980 years) and females (61.953 years). A one-way ANOVA showed a statistically significant difference in age-at-death for both sexes (F-value = 8.9512, p-value = 0.0029), indicating differences in survivorship in favor of female longevity by approximately eight years.
We explored the relationship between lesions attributed to anemia and sex, cause of death, frailty, and mortality in a modern, documented Portuguese skeletal sample. Because the skeletal sample represents people living in a time of significant socioeconomic change in Portugal, we examined our results across time. Additionally, we formally addressed the issue of selective mortality by testing the differences in mortality patterns between frail and non-frail individuals. Our research design linked frailty to demography, emphasized lesion severity and prevalence, and considered diseases that may contribute to mortality (i.e., comorbidities), while utilizing age-structured data. Numerous authors [2, 10, 53–55], state that this rigor is required to appropriately address the issues raised by Wood and coworkers  in The Osteological Paradox.