Impacts of Weather and Climate on Mortality and Self-harm in Finland

Abstract

Human beings are able to adapt to their climatic normal conditions, but weather extremes may pose a substantial health risks. The aims of this dissertation were to model the dependence of all-cause mortality on thermal conditions in Finland, and to assess changes in the relationship over the decades and regional differences in the relationships between hospital districts. Another aim was to assess impacts of weather and climate on committed and attempted suicides Finland. Various methods were applied in these studies.

Time series of all-cause mortality in three age groups in Helsinki-Uusimaa hospital district were made stationary, and thus the weather impacts were comparable over the 43-year long time period regardless of changes in population and life-expectancy. The increase in relative mortality due to hot extreme was more than due to cold extreme, when compared to seasonally varying expected mortality. However, a decrease in relative mortality in extreme temperatures over the decades was found in all age-groups, even among the 75 years and older, indicating decreased sensitivity to thermal stress in the population.

Regional differences in temperature‒mortality relationships between 21 hospital districts were studied using distributed lag non-linear models (DLNM), and the differences were assessed by meta-regression with selected climatic and sociodemographic covariates. Regional differences in the relationships were not statistically significant indicating that the same temperature-mortality relationship can be applied in different parts of the country. On the other hand, the meta-regression suggested that the morbidity indices and population in the hospital districts could explain part of the small heterogeneity in the temperature‒mortality relationships.

The study on committed suicides on the basis of 33-year long time series showed a significant negative association between suicides and solar radiation in the period from November to March, thus, a lack of solar radiation would increase suicide risk in winter. Men appeared to be more sensitive to variation in solar radiation than women. The study on weather dependence of attempted suicides in Helsinki on the basis of two shorter periods showed another difference between genders. The risk of suicide attempts of men increased with decreasing atmospheric pressure, while the risk of suicide attempts of women increased with increasing pressure.

The outcomes of this thesis can be utilized e.g. in preparedness to weather extremes in health sector and in further studies on impacts of climate change on human health.