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The effect of heat waves on mortality in susceptible groups: a cohort study of a Mediterranean and a Northern Europe city
Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Occupational and Environmental Medicine.
Rome, Italy.
Rome, Italy.
Rome, Italy.
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2015 (English)In: Environmental health, ISSN 1476-069X, Vol. 14, no 1, 30- p.Article in journal (Refereed) Published
Abstract [en]

Background: Climate change is projected to increase the number and intensity of extreme weather events, for example heat waves. Heat waves have adverse health effects, especially for the elderly, since chronic diseases are more frequent in that group than in the population overall. The aim of the study was to investigate mortality during heat waves in an adult population aged 50 years or over, as well as in susceptible subgroups of that population in Rome and Stockholm during the summer periods from 2000 to 2008.

Methods: We collected daily number of deaths occurring between 15th May and 15th September each year for the population above 50 as well as the susceptible subgroups. Heat wave days were defined as two or more days exceeding the city specific 95th percentile of maximum apparent temperature (MAT). The relationship between heat waves and all-cause non-accidental mortality was investigated through time series modelling, adjusting for time trends.

Results: The percent increase in daily mortality during heat waves as compared to normal summer days was, in the 50+ population, 22% (95% Confidence Interval (CI): 18-26%) in Rome and 8% (95% CI: 3-12%) in Stockholm. Subgroup specific increase in mortality in Rome ranged from 7% (95% CI:–17-39%) among survivors of myocardial infarction to 25% in the COPD (95% CI:9-43%) and diabetes (95% CI:14-37%) subgroups. In Stockholm the range was from 10% (95% CI: 2-19%) for congestive heart failure to 33% (95% CI: 10-61%) for the psychiatric subgroup.

Conclusions: Mortality during heat waves increased in both Rome and Stockholm for the 50+ population as well as in the considered subgroups. It should be evaluated if protective measures should be directed towards susceptible groups, rather than the population as a whole.

Place, publisher, year, edition, pages
BioMed Central, 2015. Vol. 14, no 1, 30- p.
Keyword [en]
Heat wave, Mortality, Susceptible groups
National Category
Environmental Health and Occupational Health
URN: urn:nbn:se:umu:diva-88884DOI: 10.1186/s12940-015-0012-0OAI: diva2:717860
the EU project “Public Health Adaptation Strategies to Extreme weather events–PHASE” (contract number EAHC 20101103)

Daniel Oudin Åström was funded by a grant from The Swedish Council for Working Life and Social Research (FAS:2009–0454) awarded to Professor Bertil Forsberg. This work was carried out within the EU project “Public Health Adaptation Strategies to Extreme weather events–PHASE” (contract number EAHC 20101103).

Available from: 2014-05-19 Created: 2014-05-19 Last updated: 2015-07-21Bibliographically approved
In thesis
1. On temperature-related mortality in an elderly population and susceptible groups
Open this publication in new window or tab >>On temperature-related mortality in an elderly population and susceptible groups
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Background: Climate change has increased the frequency, intensity, duration, and spatial extent of some extreme weather events, for instance heat waves. Societies today are experiencing an ongoing change in the population structure yielding an increasing proportion elderly due to increased longevity, resulting in higher prevalence of chronic and degenerative diseases. Literature suggests that the elderly and certain susceptible subgroups with chronic disease are among the most vulnerable to heat waves and elevated temperatures.

Aim: The main aims of this thesis were to expand the scientific knowledge on the short-term effects of extreme heat on mortality for the general population and certain susceptible groups in society, to investigate the development of this relationship over time and to attribute mortality to observed climate change.

Methods: Daily numbers of deaths and daily meteorological observations during three different periods were collected for present day Stockholm County, Sweden. The analyses of the relationship between mortality and temperature extremes were analysed using a time series approach. The regression models assumed the daily counts of mortality to follow an overdispersed Poisson distribution and adjustments were made for time-trends as well as confounding factors.

Results: The literature review of recent studies identified a strong relationship between heat and heat waves and increasing death rates among the elderly, particularly for respiratory and cardiovascular mortality. A statistically significant increase in total daily mortality during heat extremes in all decades investigated, as well as over the entire period, during the period 1901-2009 with a declining trend over time for the relative risk associated with heat extremes, was reported in paper II. For the period 1901-2009 cold extremes significantly increased mortality, with a more disperse pattern over individual decades and no declining trend over time. Paper III attributed increased mortality due to climate change between 1900-1929 and 1980-2009. This increase was mainly due to a large number of excess heat extremes in the latter time period. Furthermore certain subgroups of the population above 50, were in paper IV found to have significantly increased mortality during heat waves as compared to non-heat wave days.

Conclusions: Although the relative risk of dying during extreme temperature events appears to have fallen in Stockholm, Sweden, such events still pose a threat to public health. The elderly population and certain susceptible subgroups of the population experience higher relative risks of dying on heat waves days as compared to normal summer days. Some of the groups most susceptible during heat waves were identified. In order to minimize future impacts of heat waves on public health, identifying susceptible subgroups in an ageing society as well as develop strategies to reduce the impact of future temperature extremes on public health will be important.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2014. 58 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1658
Heat-related mortality, attribution, elderly, susceptible groups
National Category
Environmental Health and Occupational Health
Research subject
Occupational and Environmental Medicine
urn:nbn:se:umu:diva-89019 (URN)978-91-7601-066-2 (ISBN)
Public defence
2014-06-11, Triple Helix, Samverkanshuset, Umeå, 09:00 (English)
Forte, Swedish Research Council for Health, Working Life and Welfare, 2009-0454
Available from: 2014-05-20 Created: 2014-05-19 Last updated: 2015-04-29Bibliographically approved

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