The association between cold extremes and neonatal mortality in Swedish Sápmi from 1800 to 1895

Abstract

Background: Studies in which the association between temperature and neonatal mortality (deaths during the first 28 days of life) is tracked over extended periods that cover demographic, economic and epidemiological transitions are quite limited. From previous research about the demographic transition in Swedish Sápmi, we know that infant and child mortality was generally higher among the indigenous (Sami) population compared to non-indigenous populations. Objective: The aim of this study was to analyse the association between extreme temperatures and neonatal mortality among the Sami and non-Sami population in Swedish Sápmi (Lapland) during the nineteenth century. Methods: Data from the Demographic Data Base, Umeå University, were used to identify neonatal deaths. We used monthly mean temperature in Tornedalen and identified cold and warm month (5th and 95th) percentiles. Monthly death counts from extreme temperatures were modelled using negative binomial regression. We computed relative risks (RR) with 95% confidence intervals (CI), adjusting for time trends and seasonality. Results: Overall, the neonatal mortality rate was higher among Sami compared to non-Sami infants (62/1,000 vs 35/1,000 live births), although the differences between the two populations decreased after 1860. For the Sami population prior 1860, the results revealed a higher neonatal incidence rate during cold winter months (<−15.4°C, RR = 1.60, CI 1.14-2.23) compared to infants born during months of medium temperature. No association was found between extreme cold months and neonatal mortality for non-Sami populations. Warm months (+15.1°C) had no impact on Sami or non-Sami populations. Conclusions: This study revealed the role of environmental factors (temperature extremes) on infant health during the demographic transition where cold extremes mainly affected the Sami population. Ethnicity and living conditions contributed to differential weather vulnerability.

Neonatal Mortality and Temperature in Two Northern Swedish Rural Parishes, 1860–1899—The Significance of Ethnicity and Gender

“…The non-Sami population showed no clear seasonal pattern in neonatal mortality, yet a higher mortality was found among infants born in January and November [7]. Furthermore, our previous research showed an association between extreme winter temperatures and neonatal mortality between 1800 and 1900, during which time neonatal mortality increased during the cold winter months (monthly mean temperatures below −15 • C) compared to the milder winter months, particularly among the Sami population [6]. We also found a decreased vulnerability in the Sami population during the second half of the century, suggesting improvements in overall living conditions and health outcomes [6].…”

“…In this paper, we studied the association of daily temperature and seasonality with neonatal mortality, covering a sensitive period of an infant's life. Our previous studies, based on monthly mean temperatures, showed that Sami perinatal and neonatal mortality were influenced by extreme cold in the winter, whereas extreme cold winter temperature had no effect on the non-Sami population [6,8].…”

“…Based on information about family name, parish, occupation and family relations, an ethnical indicator that distinguished between the Sami population and the non-Sami population has been developed [39]. This ethnical indictor has been used in a variety of studies regarding marriage, fertility and mortality patterns in Swedish Sápmi [4,[6][7][8]13,23,39,40]. The available information about ethnicity does not allow a differentiation between nomadic and settled Sami.…”

“…Mortality rates in northern Sweden in particular, including in the Sápmi area (traditional land of the indigenous Sami), were sometimes as high as 250/1000 live births [5]. One of the factors associated with the high infant mortality rate in the Sápmi area is the harsh climate with long and cold winters [6,7].…”

“…While previous studies of the association between temperature and neonatal mortality among historical populations mainly used month of birth as a proxy for temperature or monthly mean temperatures [6], studies that include daily temperatures are limited [19,20]. In this study, we aimed to unravel the association between local daily temperature conditions and neonatal mortality in two Swedish rural parishes between 1860 and 1899.…”