EARLY INCREASES IN ISCHEMIC-HEART-DISEASE MORTALITY DISSOCIATED FROM AND LATER CHANGES ASSOCIATED WITH RESPIRATORY MORTALITY AFTER COLD WEATHER IN SOUTH EAST ENGLAND

Study objective-To identify the time courses and magnitude of ischaemi c heart (IHD), respiratory (RES), and all cause mortality associated w ith common 20-30 day patterns of cold weather in order to assess Links between cold exposure and mortality. Design-Daily temperatures and da ily mortality on successive days before and after a reference day were regressed on the temperature of the reference day using high pass fil tered data in which changes with a cycle length <80 days were unaffect ed (<2%), but slower cyclical changes and trends were partly or comple tely suppressed. This provided the short term patterns of both tempera ture and mortality associated with a one day displacement of temperatu re. The results were compared with simple regressions of unfiltered mo rtality on temperature at successive delays. Study population and sett ing-Population of south east England, including London, over 50 years of age from 1976-92. Main results-Colder than average days in the line ar range 15 to 0 degrees C were associated with a ''run up'' of cold w eather for 10-15 days beforehand and a ''run down'' for 10-15 days aft erwards. The increases in deaths were maximal at 3 days after the peak in cold for IHD, at 12 days for RES, and at 3 days for all cause mort ality. The increases lasted approximately 40 days after the peak in co ld. RES deaths were significantly delayed compared with IHD deaths. Ex cess deaths per million associated with these short term temperature d isplacements were 7.3 for IHD, 5.8 for RES, and 24.7 for all cause, pe r one day fall of 1 degrees C. These were greater by 52% for IHD, 17% for RES, and 37% for all cause mortality than the overall increases in daily mortality per degrees C fall, at optimal delays, indicated by r egressions using unfiltered data. Similar analyses of data at 0 to -6. 7 degrees C showed an immediate rise in IHD mortality after cold, foll owed by a fall in both IHD and RES mortality rates which peaked 17 and 20 days respectively after a peak in cold. Conclusion-Twenty to 30 da y patterns of cold weather below 15 degrees C were followed: (1) rapid ly by IHD deaths, consistent with known thrombogenic and reflex conseq uences of personal cold exposure; and (2) by delayed increases in RES and associated IHD deaths in the range 0 to 15 degrees C, which were r eversed for a few degrees below 0 degrees C, and were probably multifa ctorial in cause. These patterns provide evidence that personal exposu re to cold has a large role in the excess mortality of winter.