Excess heat and cold are both associated with increases in mortality. The temperatures at which populations are affected vary geographically. Researchers from the Queen Mary and Westfield College, London, UK undertook an observational population study to assess heat-related mortality in seven regions of Europe. They looked at mortality among people aged 65-74 in north Finland, south Finland, Germany, Netherlands, London, north Italy and Athens.

They found that:

Mortality was lowest at 14.3-17.3ºC in north Finland, and at 22.7-25.7ºC in Athens
Regions where the summers are hotter do not have significantly higher annual heat-related mortality than cooler lands
Mean annual heat-related mortalities were 304 per million population in north Finland, 445 in Athens and 40 in London
By contrast, cold-related mortality figures were much higher, at 2,457, 2,533 and 3,129 respectively.
The authors concluded that populations in Europe have successfully adapted to mean summer temperatures ranging from 13.5ºC to 24.1ºC, and may be expected to adjust to the predicted global warming with little increase in heat-related mortality. Measures to help people protect against cold in winter may allow substantial reductions in overall mortality as temperatures rise.