In all regions, mean daily mortality per million population fell as mean daily temperature rose from the lowest level experienced in the region, was roughly level over a band of 3°C, and then rose as temperature increased above this band (fig 1). The 3°C band of minimum mortality for each region was calculated and used as baseline for the region. In north Finland this band was 14.3 to 17.3°C (table ). Above this band mortality rose, producing a total of 304 heat related excess deaths per million annually. The rise was highly significant (P<0.001) despite the region having the smallest population (table ).
Annual heat and cold related mortalities per million population in people aged 65-74 living in warm and cold regions of Europe. Values are given with 95% confidence intervals in parenthesis
Population aged 65-74 and wind, humidity, and rainfall at various temperatures in study regions*
In regions with warm summers the 3°C bands of minimum mortality occurred at higher temperatures than in regions with colder summers, P=0.027 (table , fig 1). Consequently, the number of days warmer than the minimum mortality band was no greater in the hotter countries than in colder countries, and annual heat related mortality per million at these temperatures was not significantly greater in hotter regions. The upper limit of the minimum mortality band, marking the start of heat related mortality, was 17.3°C in north Finland, 22.3°C in London, and 25.7°C in Athens. The steepness of the rise in daily mortality with increase in temperature above the minimum mortality band was not significantly different in regions with warmer and colder summers. Neither annual mortality nor the steepness of the rise in daily mortality with temperature above the minimum mortality band was significantly related to the region's mean summer temperature if mortalities were expressed as a fraction of the mortality in the minimum mortality band (data not shown). The baseline mortalities in the minimum band show the well known tendency to higher mortality in colder countries. This is generally attributed to diet.
There were no systematic differences in wind speed, humidity, and rainfall at given temperatures, nor in the proportion of men in the population, that would account for minimum mortality occurring at higher temperatures in hot regions (table ). Athens had higher wind speeds, lower humidity, and less rain than other regions at 22.7 to 25.7°C, the highest 3°C temperature band common to all regions. However, the second hottest region, north Italy, had the lowest wind speeds and roughly average humidity and rain in this temperature band. Wind speeds, humidities, and rainfall were not significantly related to mean summer temperature of the region in any 3°C temperature band.
Annual cold related mortality was higher than heat related mortality in all regions (table ). Over the seven regions together, annual cold related deaths averaged 2003 per million compared with 217 per million heat related deaths (difference, P<0.001 by paired t test). Neither annual cold related mortality nor the steepness with which daily mortality rose with falls in temperature below the band of minimum mortality was significantly related to mean summer temperature of the region. For annual cold related mortality, this remained non-significant if mortality was expressed as a fraction of mortality in the minimum band (data not shown). However, the steepness of the rise in daily mortality with falls in temperature below the band of minimum mortality became significantly related to mean summer temperature (P=0.028) when expressed as a fraction of mortality in the minimum band.