Early cohort mortality predicts the rate of aging in the cohort: a historical analysis

Abstract

Early environmental influences on later-life health and mortality are well recognized in the doubling of life expectancy since 1800. To further define these relationships, we analyzed the associations between early-life mortality and both the estimated mortality level at age 40 and the exponential acceleration in mortality rates with age characterized by the Gompertz model. Using mortality data from 630 cohorts born throughout the 19th and early 20th century in nine European countries, we developed a multilevel model that accounts for cohort and period effects in later-life mortality. We show that early-life mortality, which is linked to exposure to infection and poor nutrition, predicts both the estimated cohort mortality level at age 40 and the subsequent Gompertz rate of mortality acceleration during aging. After controlling for effects of country and period, the model accounts for the majority of variance in the Gompertz parameters (about 90% of variation in the estimated level of mortality at age 40 and about 78% of variation in the Gompertz slope). The gains in cohort survival to older ages are entirely due to large declines in adult mortality level, because the rates of mortality acceleration at older ages became faster. These findings apply to cohorts born in both the 19th century and the early 20th century. This analysis defines new links in the developmental origins of adult health and disease in which effects of early-life circumstances, such as exposure to infections or poor nutrition, persist into mid-adulthood and remain evident in the cohort mortality rates from ages 40 to 90.

Fig. 1. Lexis diagram representing cohort mortality data included in the analysis. Single–year birth cohorts aged 0–10 (red lines) and 40–90 (black lines)

Fig. 2

Historical data for Sweden showing cohort mortality declines. (a) Average cohort mortality rates for the total population: selected cohorts. The spikes in mortality for the most recent two cohorts are associated with the 1918 Influenza pandemic (top panel), and (b) estimated Gompertz parameters with 95% confidence intervals for single–year birth cohorts ages 40–90 for men (blue) and women (red) (bottom panel)

Fig. 3. Gompertz parameter associations (Eq. (1)) with cohort mortality for the nine European countries ages 0–10 years (q0–10). Slope is the mortality rate acceleration, ages 40–90; In a is the log-mortality rate calculated at age 40