The Relative Effects of Shocks in Early‐ and Later‐Life Conditions on Mortality

Abstract

The relative importance of cohorts' early-life conditions, compared to later period conditions, on adult and old-age mortality is not known. This article studies how cohort-level mortality depends on shocks in cohorts' early- and later-life (period) conditions. I use cohorts' own mortality as a proxy for the early-life conditions, and define shocks as deviations from trend. Using historical data for five European Countries i find that shocks in early-life conditions are only weakly associated with cohorts' later mortality. This may be because individual-level health is robust to early-life conditions, or because at the cohort level scarring, selection, and immunity cancel each other. Shocks in period conditions, measured as deviations from trend in period child mortality, are strongly and positively correlated with mortality at all older ages. The results suggest that at the cohort level changing period conditions drive mortality variation and change.

Early-life disease exposure and associations with adult survival, cause of death, and reproductive success in preindustrial humans

“…Our study, however, uses data from 100 cohorts of a preindustrial population and controls for variation in social class and birth circumstances to provide a unique snapshot of how early-life conditions may have influenced human populations for much of our evolutionary history (6, 7). We conclude, in agreement with several other authors (37,39,40), that the influence of improved adult, rather than childhood, conditions is likely to have driven recent improvements in life expectancy.…”

“…Previous studies have found evidence for links between early-life cohort mortality rate and later survival (4,5,8), but without considering that such a measure of disease exposure could be confounded by spatial variation, social status, other intrinsic and extrinsic conditions as well as disease exposure, and improvements in living conditions and hygiene across time. Demographic studies have applied statistical techniques such as Hodrick-Prescott decomposition to trending environmental data and found generally weak associations between early and later cohort mortality (37)(38)(39)(40), although some of these studies have still detected significant correlations (19,41). By applying Hodrick-Prescott decomposition, we were able to account for declines in death rates from infection across time by using deviations from this trend as our measure of early-life disease exposure (Fig.…”

“…For example, early infections may have negative associations with later health through chronic physiological "scarring," but may also have positive associations due to acquired immunity or selection of the most robust individuals who were able to survive the harsh early environment (42). There may also be changes in the factors that influence mortality in different parts of the life course, such that the relative importance of scarring and selection may vary with age (43) and the effects of early adversity may be short-lived, or be negligible in comparison with events that occur in adult life (39). A study using data from Sweden, collected 1813-1968 and calculating early-life disease risk based on neonatal mortality rates, showed that effects of exposure on mortality varied with age: Individuals born during times of higher neonatal mortality rates showed higher mortality initially but lower mortality in later life (44).…”

“…Based on previous studies examining links between early exposure to mortality and later-life health and fitness (19,(38)(39)(40), we aimed to estimate an individual's experience of infectious diseases in their first 5 y of life, as illustrated by the prevalence of death from infectious diseases recorded by the church (54). Because children and adults are vulnerable to different diseases in this population (SI Appendix, Tables S3 and S5), we recorded the number of individuals aged 0-10 y who were alive in the parish in each year, 1751-1855, a total of 194,182 person-y (SI Appendix, Table S2), during which time 4,780 children died of a known cause, 73% of which were due to infectious diseases (SI Appendix, Table S3); 22% of deaths were from an unknown disease, which we included in the infectious category.…”

Early-life conditions and adult mortality decline in Dutch cohorts born 1812–1921

“…However, using historical data from England and Wales, Finland, the Netherlands, and Sweden, Myrskylä (2010) found that shocks in early-life conditions, proxied by a cohort's infant mortality, are only weakly associated with a cohort's later mortality.…”