Cold-related deaths have been noted for centuries.

The results show that the percentage increases in all-cause and RD mortality with fall in temperature were greater, and that protective measures against a given degree of cold were fewer, in regions with mild winters.

Although we know that the middle-aged and elderly should wear protective clothing and keep active in cold weather outdoors, our surveys show that in relatively warm countries they often fail to do so.

As recently described by Fowler et al.,22 the EWD index (EWDi) is calculated by comparing the number of deaths that occur in:
† the 4 months of winter (these are pre-designated as December–March in the Northern hemisphere);
† the four autumn months preceding that winter (August– November)
† the four spring months following on from that winter (April – July)

Several known effects of cold on the body could account for cold-related deaths. Arterial thrombosis is promoted by the haemoconcentration3,4 induced by cold, and rapid coronary deaths could result from rupture of atheromatous plaques during hypertension and cold- induced coronary spasm.5–8,22

Suppression of immune responses by stress hormones during cold exposure is likely to reduce resistance to respiratory infection, as will direct effects of cold on the respiratory tract;23,24 these direct effects could also cause bronchoconstriction.25

Acute-phase reactions to such respiratory infection13,14 can then be expected to increase further the risk of arterial thrombosis. The results do not rule out other factors such as previous temperature experience, or low vitamin C intake in winter.26,27

However, the associations shown in the results between mortality and protection against cold stress strongly suggest that excess winter mortality could be reduced substantially by improved protection from cold—particularly in countries with warm winters where the need for cold-avoidance was less obvious, and measures taken against it less effective.

(index) Heating degree days (HDDs)