Dissertation

Long-term trends in mortality differences: register-based studies in Finland, 1970-2020

Abstract

Mortality has declined substantially over the last century, reflecting significant overall health improvements across populations. Yet despite the overall improvement, notable differences in mortality risks persist across population subgroups, with evidence suggesting that these differences have even widened in recent decades, at least when measured by socioeconomic position. However, mortality differences are not solely shaped by socioeconomic inequalities but also by other dimensions, such as where people live, with whom they live, and frailty to seasonal mortality risks. These aspects have received less attention, particularly from a long-term perspective. This thesis examined long-term trends in mortality differences in Finland since the 1970s in three independent sub-studies, each focusing on distinct and less-studied dimensions of mortality variation: area of residence, living arrangements, and seasons of the year. The studies were based on comprehensive individual-level total population data of those aged 30 and above, drawn from administrative registers and covering the period from 1970 to 2020. Over the past five decades, variation in mortality rates between municipalities increased markedly, largely explained by widening differences in population age structures. Once these age structure differences were accounted for, mortality differences remained unchanged amongst those age 70 and over. In contrast, disparities widened at younger ages, with the most consistent increase observed among working-age men (30–49), for whom area differences were the most pronounced. Men in this age group living in higher-mortality municipalities faced, on average, a 33% higher hazard of death compared to those in lower-mortality municipalities, up from 17% in the early 1970s. This increase in mortality variation was largely driven by external causes of death and linked to growing socioeconomic disparities between municipalities. Living arrangements that involve co-residence with a partner have traditionally been linked to lower mortality. This advantage persisted between 1990 and 2020. Throughout this period, all-cause mortality was lowest among men and women living with a partner, while those living alone or with persons other than a partner or child faced up to a fivefold excess mortality risk compared to those living with a partner and children. Although mortality declined across all living arrangement groups and absolute differences in mortality rates narrowed, relative disparities widened partially due to the declining mortality level. The relative mortality disadvantage increased particularly in the growing group of individuals living alone. Adjusting for socioeconomic factors attenuated mortality differences between living arrangement categories only modestly but their contribution grew slightly towards the end of the study period. Mortality typically follows a seasonal pattern, with higher mortality rates observed during winter months, particularly among the older population. Since 1970, excess winter mortality steadily declined in Finland. Yet despite this overall decline, winter mortality rates consistently remained higher compared to non-winter rates, with approximately 12% higher mortality observed during winter months in the most recent two decades. While older individuals, and those with dementia or living in institutional settings, were identified as being more vulnerable to winter mortality, the increased risk of winter death extended beyond these groups in the population aged 60 years and over. No differences were observed between income groups. Overall, these findings demonstrate that while mortality has continuously declined over the past decades, disparities between the dimensions studied in this thesis persist. However, some differences have widened, others have remained stable, and some have narrowed. The results further show that the factors driving mortality differences, and their changes vary across contexts, with socioeconomic factors playing different roles in explaining the trends over time. Taken together, insights from this study extend perspectives on the long-term developments of mortality disparities and emphasise the need for holistic, sustained, and coordinated efforts to address them.