In the northern hemisphere, mortality increases in the winter. This is in large part because influenza is a winter phenomenon, and old people are vulnerable to infection and downstream consequences of infection. Cold weather provides a number of opportunities beyond infection for additional stresses to be placed on an aged body, however. An important characteristic of the frailty of old age is an inability to resist stresses that younger people would take in their stride, instead tipping over into the downward spiral to mortality. Researchers here survey the seasonality of human mortality, quantifying the overall size of the effect.
Seasonal fluctuations in mortality affect annual life expectancy at birth (e0). Nevertheless, evidence on the impact of seasonal mortality on longevity is very limited and mainly restricted to assessing season-specific mortality levels due to shocks (e.g., heatwaves and influenza epidemics). We investigated the influence of seasonality in mortality on life expectancy levels and temporal trends across 20 European countries during 2000-2019. We used harmonised weekly population-level mortality data from the Human Mortality Database. Seasonal contributions to life expectancy at birth and age 65, by sex, were estimated using the excess mortality approach and decomposition analysis. Time-series analysis was used to evaluate the impact on long-term mortality trends.
Seasonal mortality had a substantial but stable impact on e0 between 2000 and 2019. On average, we found an annual reduction in life expectancy due to seasonal excess mortality of 1.14 years for males and 0.80 years for females. Deaths in the elderly population (65+) were the main driver of this impact: around 70% and 90% of these reductions in life expectancy were attributable to older ages. Excess mortality in winter had the strongest impact on annual life expectancy, especially in Portugal and Bulgaria (around 0.8-year loss on e0). The study revealed significant cross-country variations in contributions of seasonal mortality. The most pronounced effects were observed in winter months and at older ages. These findings underscore the need for timely and targeted public health interventions to mitigate excess seasonal mortality.
Link: https://doi.org/10.1136/jech-2024-223050
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