Cold Extremes and Impacts on Health 6

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6 Cold Extremes and Impacts on Health

J. Hassi

Abstract

A special feature of the future climatic change is the climate variability in particular the frequency and intensity of extreme conditions. Cold spells will remanin a problem within Europe even under the circumstances of climatic changes. With Britain’s predicted increase in environmental temperature by 2 °C during the next 50 years, seasonal mortality during the cold months of the year still will present the majority of excess mortality. Epidemiological evidence has indicated a causal relationship between mortality and cold weather. Th e most important diseases associated with cold-related excess mortality are ischaemic heart disease, cerebro-vascular disease and respiratory disease, especially infl uenza. Body cooling may off er a better explanation for the cold-related excess mortality than environmental temperature.

Th e goals of public health activities related to the health impact of cold extremes are to reduce pre- mature deaths, the amount of disease and injuries, disease-produced discomfort, sickness and disability in the population. In order to evaluate the prevention of cold exposure-related excess mortality, we need the collaboration between health care, weather services and other offi cials to produce usable preventive action models. Th e defi nition of public health programmes aimed at preventing cold-related mortality needs further research. Th e prevention of cold injuries and illnesses is more the responsibility of health care providers and it requires practical information, education and professional support.

Introduction

Th ere is scientifi c consensus that the composition of the atmosphere is changing, thereby altering the ra- diation balance of the Earth’s atmospheric system and producing global warming. Climate change during the 21st century is predicted to be rapid and large, although there are many associated uncertainties. A special feature of the predicted change is the variability of the future climate and especially the occurrence of extreme conditions. Th e latter include the occurrence of anomalously high and low temperatures, pre- cipitation amounts and wind speeds. Even in the circumstances of climate warming, extreme cold spells remain possible which could be detrimental to health. Mortality is subject to seasonality. In many temperate countries ‘all-cause mortality’ as well as cardiovascular and respiratory mortality are higher during winter months. Some epidemiologist’s use the notion of excess winter mortality to describe this seasonal phenomenon. Most European countries suff er from 5 – 30 % excess winter mortality [19].

Th e average annual excess mortality related to cold climate has decreased [27] and will decrease even further in the future, while excess mortality related to heat will increase. Despite this, with, for example, Britain’s predicted increase in environmental temperature by 2 °C during the coming 50 years, mortality related to cold climate will still represent the majority of mortality excess related to extreme temperatures [26].

Seasonal changes in human health have been recognized for more than 2000 years [2] and excess

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Cold Extremes and Impacts on Health

winter mortality has been known for hundreds of years [45]. In more recent times scientifi c research has documented dramatic rises in mortality every winter, and smaller rises during unusually hot summers.

Mortality fi gures based on monthly, rather than daily, mortality statistics under-estimate the problem [26].

Special attention has been given to excess winter mortality in Europe during the last years [19,43] and deaths from excessive cold have also been epidemiologically quantifi ed [13].

Less recognition has been given to the public health actions to prevent the negative health impacts of cold temperature [35]. In evaluating the need for preventive and protective public health actions, it is important to recognize not only excess cold mortality, but also cold injuries, illnesses and physiological cold stress, all of which aff ect health and performance limitations.

Cold mortality at different daily temperatures

Environmental temperatures are associated with increased daily mortality, not only in countries having cold winters but also in warmer countries with milder winters, such as in the Mediterranean countries.

Th e relationship is generally a non-linear J, or V shaped. Th e lowest mortality related to daily environmental temperature is seen at higher environmental temperatures in countries with the warmest summers ( > Fig. 1) [9, 10, 44]. Th is suggests that diff erent populations adapt to their environmental temperatures.

Daily mortality in Britain is lowest when the outdoor temperature is around +18 °C. Reduction in temperature below this level cause about 40,000 excess deaths per year relative to the number observed at the temperature of minimum mortality. Apart from the special case of heat-waves, warm weather in Britain causes around 1000 extra deaths per year [26].

Th e Eurowinter group studied whether increases in mortality per 1 °C fall in temperature diff er across various European regions and related any diff erences to average winter climate and to measures to protect against cold. Th e fi ndings were that the percentage increases in all-cause mortality per 1 °C fall in temperature below 18 °C were greater in warmer regions than in colder regions, e.g. Athens 2.15 % [95 % CI 1.20 – 3.10] versus south Finland 0.27 % [0.15 – 0.40]). At an outdoor temperature of 7 °C, the mean living- room temperature was 19.2 °C in Athens and 21.7 °C in South Finland; 13 % and 72 % of people in these regions, respectively, wore hats when outdoors at 7 °C.

Multiple regression analyses (with allowance for sex and age, in the six regions with full data) showed that high indices of cold-related mortality were associated with high mean winter temperatures, low living-room temperatures, limited bedroom heating, low proportions of people wearing hats, gloves, and anoraks, and inactivity and shivering when outdoors at 7 °C (p < 0.01 for all-cause mortality and respiratory mortality; p > 0.05 for mortality from ischaemic heart disease and cerebrovascular disease) [43]. Th e Eurowinter group noted that a lower proportion of people wear hats and gloves in slightly cool outdoor temperatures (+7 °C) [43]. It could be hypothesized that the higher cold-related mortality of populations in regions where extreme cold occurs less frequently is associated with a poorer adaptation to the cold.

Deaths outside of hospitals in the USA are strongly associated with cold temperatures, irrespective of gender. Stronger associations with cold are seen for those aged less than 65 years. Th e strong out-of-hospital eff ect modifi er was more than fi ve times greater than in-hospital deaths, supporting the biological plausibility of the association [33]. In Europe, exposure to cold increases the risk of coronary and cerebral thrombosis in elderly people with atheromatous arteries [26]. In recent years, epidemiological evidence has accumulated indicating a causal relationship between mortality and cold weather and today a critical discussion of weather as a confounder is not as common as it used to be.

Exposure to cold has an important and partially direct eff ect on daily mortality [1]. Th e most important diseases associated with cold related excess mortality are ischaemic heart disease, cerebro-vascular disease and respiratory disease [23], especially infl uenza [1]. Approximately half of the excess deaths are

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⊡ Fig. 1

Mortality at different mean daily temperatures. Pooled data for each region at age 55+, 1971 – 1997. The areas of circles are proportional to the number of days at each temperature. (Donaldson GC, Keatinge WR, Nayha S. Changes in summer temperature and heat-related mortality since 1971 in North Carolina, South Finland, and Southeast England. Environmental Research 200; 91(1):1-7 as figure 1)

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due to coronary thrombosis, with a peak two days following a cold spell. Some later coronary deaths occur secondarily to respiratory disease. One-forth of excess mortality is caused by respiratory disease, peaking about 12 days aft er the peak of a cold spell [26]. Th e variance of winter-time temperatures modifi es the eff ects of very cold days on respiratory mortality [5]. Associations between ischaemic heart disease deaths and respiratory deaths that are seen in the temperature range of 0 - 15 °C, were reversed for temperatures a few degrees below 0 °C, probably due to multifactorial causes [8].

Th eories about the mechanisms of cold-related cardiovascular mortality have tended to focus on changes in the circulation and haemostasis that may pre-dispose to thrombotic events [3, 32, 42, 46, 47] as a result of body cooling [14, 41]. Coronary and cerebral mortality are related to a strong increase of blood pressure as a consequence of cold exposure and associated peripheral blood vessels constriction, decreas- ing blood volume and the activation of thrombogenic factors. Th is may lead to thrombosis in cerebral and coronary vessels causing deaths. Th ese and respiratory infections explain the majority of winter deaths.

Keatinge and colleagues place more emphasis on personal behaviours, and have argued that much of the excess winter mortality from arterial thrombosis is related to cold exposure from “brief excursions outdoors rather than to low indoor temperature”[43, 25].

Th e discrepancy of the fi ndings of excess cold mortality associated with the level of environmental cold exposure indicates some other, more direct, causal association. Th e skin temperatures associated with environmental cold exposure commonly decrease, especially in the extremities. During cold winter months even in well-insulated Nordic homes, foot skin temperatures of the elderly are lower than in summer months. Th ese results indicate that man is commonly cold stressed during cold exposure [28].

Body cooling may act as one mediator of cold environmental temperature off ering an explanation for cold related excess mortality better than the diff erent possible causal pathways for cold related excess mortality are widely discussed [4].

Winter mortality

Th e rate of mortality increases seasonally every winter. On average this excess winter mortality in most European countries varies from 5 % to 30 % [6, 19, 31]. However, within a single country excess winter mortality may vary by as much as 40 % from year to year [12]. Cardiovascular and respiratory causes of death are most strongly linked to seasonal changes in temperature. Elderly people and those with impaired health or suff ering from social conditions are the most susceptible to the impact of weather changes [2].

During the last decades there has been a decline in infl uenza epidemics, which account for less than 5 % of the excess winter mortality in Britain [26]. Countries with mild climates show higher levels of excess winter deaths associated with socio-economic conditions and housing standards as explaining variables [43]. Countries with high levels of income poverty and inequality have the highest coeffi cient of seasonal variation in mortality [12]. During cold periods the availability of continuous electricity and heating is es- sential for human well-being. Th ere are numerous examples of accidents in electricity supply and cut-off s in the Russian Federation and many eastern European countries. In the case of heat supply cut-off s, when outdoor temperatures are below 10 °C (this period lasts 3 – 5 months a year in the Northern countries), indoor temperatures fall below 15 °C. For example, during the winter of 2002 – 2003, 20 Russian cities had problems with residential heating systems. More than 1 million people experienced temperature discomfort, which lasted for longer than a month. (Revich, personal communication). Freezing to death and accidental hypothermia resulting in frostbites is extremely rare as a consequence of lack of heating in homes;

the rare extreme cases have been observed during the very cold winters in places like Northern Russian Federation and the Baltic States.

Winter rainfall and excess deaths are signifi cantly associated (a regression coeffi cient of 0.54, p < 0.001) [19]. Cold spells increase mortality [8, 39], but their relative importance is unknown. A recent study

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conducted by Wilkinson et al, (forthcoming) in the United Kingdom, assessed factors for winter excess mortality in the over 75 years old. A relationship between winter mortality and cold was found, however the fi ndings suggest that the risk of excess winter death is more widely distributed within the elderly population than hitherto has been appreciated, and is less related to factors such as access to heating than had been thought. Th is may limit the potential health benefi ts of government energy effi ciency initiatives that are specifi cally targeted at low-income households.

Hypothermia and cold-induced injuries

Accidental hypothermia is known to be a hazard to elderly people in temperate and cold climates [37].

Hypothermic deaths are seen as a special consequence of unsatisfactory dwellings. Th e appearance of outdoor hypothermic deaths is strongly related to the awareness of hypothermia and protection against cold. Th e typical victim of outdoor hypothermic death in Finland is a resident of an elderly persons’ home forgetting his/her way back home from their walking trips during cold spells.

Th e total injury rate may change as a consequence of both direct or indirect eff ects of cold. Causal relationships between diff erent injury sources and accident types, the nature of the injury and the degree of the disability sustained from injury, may also have diff erent pathways ( > Fig. 2).

In the U.S.A. the majority of occupational outdoor cold exposure injuries occur during the few coldest winter days. Wind speed strongly increases the injury rate. Freezing, strains and sprains are commonly represented among the cold exposure injuries. Cold exposure injuries display a strong negative relationship with temperature [40]. Occupational slips and falls exhibit a similar negative correlation with temperature. In the mining industry in the U.S.A. the higher rates are linked to about 0 °C [16]. Unintentional injury occurs least frequently at a temperature of about +20 °C and increases at lower and higher ambient temperatures [36]. Cold environmental temperature is usually a secondary source of injury, rather than a primary one. Cold exposure injuries are reported with much higher frequencies in questionnaire studies than in records, which tend to underestimate this type of injury [34]. Accidental cold exposure occurs mainly outdoors, in socially deprived people, workers, alcoholics, the homeless, the elderly in temperate cold climates [37]. Th e risk of suff ering frostbite increases with age [21].

Th e onset of frostbite resulting from exposure to cold air appears at an environmental temperature of –11 °C. Wind, high altitude and wet clothing lead to onset of freezing injury at higher environmental temperatures [7]. Th e incidence of more serious frostbite requiring hospital treatment increases at temperatures of –15 °C and below. Such injuries have been reported to be more common in metropolitan areas than in other types of living resorts in Finland. Th e risk of suff ering frostbite increases with age. [21].

Injury from frostbite is comparable to burns with respect to the immediate consequences and may range in severity from mild to more severe functional limitation of the injured area, to sick leave, or, in some cases, to hospitalization [21]. Th e latent symptoms of frostbite which are most common include a local hypersensitivity to cold and pain in the injured area, cold-induced sensations and disturbances of muscular function, and excessive sweating. Th ese latent symptoms have been shown to have a negative impact on occupational activities [13]. Cold injuries need to be recognized as one of the health impacts of cold weather.

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Actions of Public Health for Preventing Cold-Related Health Impacts

Predicting and alerting a city’s residents of imminent dangerous weather conditions, especially during the summer, has been practiced in large metropolitan areas of the USA: health-watch warning systems are based on meteorological forecast variables [22], but have been only slightly modifi ed for cold spells.

Warm housing is a key element in the prevention of excess cold mortality [26]. Physical changes in housing design cannot be expected to happen very rapidly and probably do not represent the most eff ective preventive action to be taken against cold-related excess mortality [24]. Modelling of seasonal variations in mortality and domestic thermal effi ciency indicates that low energy effi ciency could explain 5 % of excess winter deaths [19].

Th e responses of people to their thermal environments during the winter months in Norway indicate that they are more cold-stressed at this time of the year [28]. Environmental cold may provoke cardio- pulmonary symptoms independent of sex and age [17] and also provoke other types of symptoms [15].

⊡ Fig. 2

Associations between environmental cold and injuries.

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Protection against outdoor body-cooling is one method of preventing excess cold mortality. In northern countries, people are more experienced and successful in using eff ective cold-protective clothing [43]. In the Nordic countries, some intervention programmes have been established aiming to develop behav- ioural changes in cold-exposed workplaces, and some methodological tools have been produced for the prevention of cold stress through the actions of health care personnel [18, 20, 29, 30, 38]. Th ey have been used as a base to develop an ISO standard for working practices in cold environments: ISO CD 15743 (2002).

Th ere is a need to defi ne preparative actions for preventing cold-related impacts on health. Th e defi - nition of public health programmes to prevent cold-related mortality needs further research in order to evaluate: 1) the populations at risk, 2) the lag time of the eff ect, 3) the eff ect of cardio-vascular and respiratory morbidity, 4) the role of respiratory mortality, and 5) the signifi cance of other meteorological variables [2]. To prevent cold exposure-related excess mortality, we need collaboration between health care, meteorologists and other offi cials to produce usable preventive action models. Th e prevention of cold injuries and illnesses is very much the responsibility of health care providers, requiring practical information, education and professional support.

Conclusions

In the research published in recent years epidemiological evidence has accumulated indicating a causal relationship between mortality and cold weather. Evidence of the importance of cold-related sicknesses and injuries is growing. Th e importance of cold- related health impacts in the whole of Europe today and in the future is not well recognized in the public health sector. Th ere is a need to evaluate more by research cold induced morbidity, mortality and meteorological variables. Despite some models and standards for prevention of cold stress, we need more collaboration between health care, weather broadcasting and other offi cials to produce usable preventive action models and their national applications in Europe.

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