Seasonal fluctuations in mortality have a substantial impact on annual life expectancy at birth (e0) in Europe. However, the exact contribution of seasonality on longevity remains largely unknown. In this article, we investigate the influence of seasonal mortality patterns on life expectancy levels and temporal trends across 20 European countries during 2000-2019.
Patterns of Seasonal Mortality
Our analysis of harmonized weekly mortality data from the Human Mortality Database reveals significant cross-country variations in the impact of seasonal excess deaths. On average, we found an annual reduction in life expectancy due to seasonal mortality of 1.14 years for males and 0.80 years for females. Notably, around 70% and 90% of these reductions were attributable to the older population (aged 65+).
The most pronounced effects were observed during the winter months, especially in Southern and Eastern European countries like Portugal and Bulgaria, where seasonal excess mortality led to a loss of around 0.8 years in e0. In contrast, Northern countries like Sweden and Finland were less affected by winter-related mortality spikes.
In comparison, the impact of summer heatwaves on life expectancy was relatively smaller. For example, the 2003 heatwave reduced e0 by only 0.3 years in France and Spain. This finding may be partly explained by the limited inclusion of Mediterranean countries in our analysis, which are historically more vulnerable to heat-related mortality.
Trends in Seasonal Mortality
While the median across the 20 European countries showed a decreasing trend in the total contribution of seasonality to life expectancy, the country-specific analysis revealed a more heterogeneous pattern. Some nations, like Bulgaria and Estonia, experienced a statistically significant decline in the impact of seasonality over time for both males and females.
However, we also identified concerning trends in a few countries. Swedish females and Polish, Slovak, and German males exhibited increasing burdens of seasonal mortality on life expectancy. These diverging trajectories underscore the need for further investigation and targeted public health interventions to address the persistent and, in some cases, growing impact of seasonality.
Impact on Life Expectancy Levels
Our findings highlight the substantial influence of seasonal mortality on life expectancy levels in Europe. The observed effect on e0 amounted to approximately 400,000 deaths per year across all the studied countries. Interestingly, the impact was almost entirely driven by excess mortality in the elderly population (65+).
When considering remaining life expectancy at age 65 (e65), the burden of seasonal excess mortality was even more pronounced. On average, removing season-specific excess deaths would increase e65 by 0.78 years for males and 0.74 years for females, accounting for around 70% and 90% of the total impact, respectively.
The most affected countries in terms of e65 were Portugal, Estonia, Bulgaria, and Latvia, where seasonal excess mortality led to a loss of 1.3-1.4 years for both sexes.
Long-Term Trends in Life Expectancy
Examining the impact of seasonality on long-term trends in life expectancy, we found that the improvements in e0 during 2000-2019 would have been marginally faster in the absence of seasonal excess mortality. However, this effect was generally small, indicating a lack of substantial progress in reducing the public health burden of seasonality.
Interestingly, a few exceptions were observed, such as in Hungary, Poland, and Slovakia, where the elimination of seasonal excess mortality could have led to additional gains of around 0.3-0.4 years in e0 for both males and females. These findings suggest that targeted interventions to mitigate seasonal mortality may have the potential to accelerate longevity improvements in certain European countries.
Causes of Seasonal Mortality
The drivers of elevated seasonal mortality are multifaceted, involving a complex interplay of environmental factors, infectious diseases, and chronic conditions.
Environmental factors, such as extreme temperatures, play a crucial role. Winter excess mortality, often driven by cardiovascular and respiratory diseases, has been the dominant contributor to seasonal life expectancy losses. This is likely due to the increased physiological stress and vulnerability to illnesses during colder months.
In addition, influenza epidemics have been a key direct driver of winter mortality spikes, especially in the older population. Severe influenza seasons, such as those observed in 2004/2005, 2009/2010, and 2014/2015, significantly impacted life expectancy levels across Europe.
The role of summer heatwaves, while less pronounced than winter effects, should not be overlooked. These extreme temperature events can disproportionately affect vulnerable groups, particularly the elderly with pre-existing medical conditions.
Implications for Public Health
The findings of this study underscore the need for timely and targeted public health interventions to mitigate the substantial burden of excess seasonal mortality in Europe. Developing effective early warning systems and promoting epidemic and extreme weather preparedness are crucial steps.
Implementing policies that provide social protection and financial aid during high-risk seasons, especially for the elderly and other vulnerable populations, can help alleviate the impacts of seasonal mortality shocks. Enhancing healthcare capacity and disease surveillance in Southern and Eastern European countries may also be beneficial in addressing the regional disparities observed in our analysis.
Moreover, the potential growing impact of climate change on seasonal mortality patterns requires close monitoring and proactive adaptation strategies, such as improving building insulation and heatwave response plans. Integrating seasonal mortality considerations into future epidemiological and demographic research and forecasting will be essential for developing comprehensive public health strategies.
By addressing the persistent and, in some cases, increasing burden of seasonal mortality, policymakers and public health authorities can work towards improving longevity and population health outcomes in the face of rapidly aging societies and evolving environmental challenges.
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