Seasonal blood pressure changes: which ambient temperature should we consider?

Abstract

ost countries suffer from 5 to 30% excess wintermortality (EWM),themajorityofadditionalwinterdeaths being caused by cerebrovascular diseases,which may be related, among other factors, to the pressoreffect of cold weather. The possibility to control the bloodpressure (BP) changes associated with low environmentaltemperatureisthusarelevantissue,forbothphysiciansandpublic health officers. In this regard, previous investi-gations, aswellasrecommendations given to citizens, havebeen developing into two different directions, underlyingthe importance of indoor or outdoor temperature, respect-ively,althoughthehealthimpactofcoldstrainseemstobeamore complex issue.The diffusion of effective systems for heating homes hasalways been considered as an important element in thepromotion of public health, especially in world regionscharacterizedbycoldwinters.Toreducetheenvironmentalimpact of ambient indoor heating and at the same time tooptimize its effects, there is now increasing attentiontowards technologies that can improve heating systemsefficiency, by reducing heat loss from homes walls, doorsand windows.These efforts seem to have been rewarding because,usinga5-yearmovingaverage,whichsmoothensoutshort-termfluctuations,excesswinterdeathshavebeendecliningsteadily since 1960–1961 up to current times. However, theimportance of thermal efficiency standards in relation tohousing is not equally felt as an important issue in thedifferent European countries. This may be partly due to theobservation that, in Europe, although mortality doesincrease as weather gets colder, differences in outdoortemperature only explain a small amount of the variancein winter mortality, and high levels of EWM can occurduring relatively mild winters [1]. More precisely, Healey[2]showed thatEWMvariedwidelywithin Europe, andthatcountries with very low outdoor winter temperatures inScandinavia and Northern Europe, such as Finland andGermany, somehow unexpectedly had very low rates ofEWM, whereas countries with very mild winter tempera-tures in Southern Europe, such as Portugal and Spain,displayed very high rates of EWM.Infact,Europeancountrieswithmilderwintersalsotendto have homes with poorer thermal efficiency (e.g. fewerhomes have cavity wall insulation and double glazing),which makes it harder to keep homes constantly warmduring winter [2]. Available data on cross-country thermalefficiencystandardsinhousingindicatethatthosecountrieswith the poorest thermal housing efficiency (Portugal,Greece,Ireland,theUK)doindeeddemonstratethehighestexcess winter mortality [2].Thesame epidemiological datacan, however,beread ina different perspective. The behavioural capability to copewith cold weather was also shown to display quite widevariations within Europe. The Eurowinter group [3]reported that, compared with people living in countrieswith cold winters, individuals from warmer countries wereless likely to wear warm protective clothing in coldweather. The same international survey showed an inde-pendent association of outdoor, as well as indoor, lowambient temperatures with excess mortality in suchcountries during cold weather [3].People in the retirement age are particularly vulnerableto winter temperatures, and show higher mortality rateswith cold weather. Indeed, in Great Britain, blue collars atworking age (50–59 years) had lower cold weather-related mortality as compared either with their wives ofsimilar age or with men of the same social class afterretirement age (65–74 years). These observations suggestthat body internal heat production from manual workprotected men of working age against daytime cold-related stress, as well as against the associated risk ofhigher mortality.Moreover, elderly people living in sheltered houses thatwere fully heated, but who often went outdoors, had asmuch winter mortality as the general elderly populationincluding those living in less well heated houses [4]. This isnotsurprising,sincethemajorityofadditionalwinterdeathsare caused by cerebrovascular diseases, and, for example,coldtemperature-relatedstressaffectingpeoplewaitingata