Ambient Temperature and Morbidity: A Review of Epidemiological Evidence
Xiaofang Ye1, Rodney Wolff2, Weiwei Yu1, Pavla Vaneckova1, Xiaochuan Pan3, Shilu Tong1
1 School of Public Health and Institute of Health and Biomedical Innovation, and, 2 Mathematical Sciences Discipline, Faculty of Science and Technology, Queensland University of Technology, Brisbane, Queensland, Australia, 3 Department of Occupational and Environmental Health, Peking University School of Public Health, Beijing, China
Environ Health Perspect 120:19-28 (2011). http://dx.doi.org/10.1289/ehp.1003198 [online 08 August 2011]
Objective: In this paper, we review the epidemiological evidence on the relationship between ambient temperature and morbidity. We assessed the methodological issues in previous studies and proposed future research directions.
Data sources and data extraction: We searched the PubMed database for epidemiological studies on ambient temperature and morbidity of noncommunicable diseases published in refereed English journals before 30 June 2010. Forty relevant studies were identified. Of these, 24 examined the relationship between ambient temperature and morbidity, 15 investigated the short-term effects of heat wave on morbidity, and 1 assessed both temperature and heat wave effects.
Data synthesis: Descriptive and time-series studies were the two main research designs used to investigate the temperature–morbidity relationship. Measurements of temperature exposure and health outcomes used in these studies differed widely. The majority of studies reported a significant relationship between ambient temperature and total or cause-specific morbidities. However, there were some inconsistencies in the direction and magnitude of nonlinear lag effects. The lag effect of hot temperature on morbidity was shorter (several days) compared with that of cold temperature (up to a few weeks). The temperature–morbidity relationship may be confounded or modified by sociodemographic factors and air pollution.
Conclusions: There is a significant short-term effect of ambient temperature on total and cause-specific morbidities. However, further research is needed to determine an appropriate temperature measure, consider a diverse range of morbidities, and to use consistent methodology to make different studies more comparable.
Key words: climate change, heat wave, hospital admission, morbidity, review, temperature
Address correspondence to S. Tong, School of Public Health, Queensland University of Technology, Victoria Park Rd., Kelvin Grove, QLD 4059, Australia. Telephone: 61 07 3138 9745. Fax: 61 07 3138 3369. E-mail: firstname.lastname@example.org
X.Y. was funded by a Queensland University of Technology Fee Waiver scholarship. S.T. was supported by National Health and Medical Research Council Research Fellowship (553043).
The authors declare they have no actual or potential competing financial interests.
We thank L. Turner at Queensland University of Technology for his useful comments on the early version of the manuscript.
Received 10 November 2010; accepted 08 August 2011; online 08 August 2011.
It is widely accepted that climate change is occurring and that it is caused mainly by increased emissions of anthropogenic greenhouse gases, particularly over the last few decades [Intergovernmental Panel on Climate Change (IPCC) 2007a]. Global mean temperature increased by 0.07°C per decade between 1906 and 2005, compared with 0.13°C per decade from 1956 to 2005 (IPCC 2007b). Not only has the average global surface temperature increased, but the frequency and intensity of temperature extremes have also changed [IPCC 2007a; World Health Organization (WHO) 2008]. Heat wave episodes have been associated with significant health impacts, for example, in 1995 in Chicago, Illinois (Semenza et al. 1999), in 2003 in Europe (Cerutti et al. 2006; Johnson et al. 2005; Larrieu et al. 2008; Mastrangelo et al. 2007; Oberlin et al. 2010), in 2006 in California (Knowlton et al. 2009), and in 2009 in southeastern Australia (National Climate Centre 2009). In addition, episodes of extreme cold (cold spells) are a concern in high-latitude regions (Pattenden et al. 2003) such as Russia (Revich and Shaposhnikov 2008), the Czech Republic (Kysely et al. 2009), and the Netherlands (Huynen et al. 2001).
The effect of ambient temperature on morbidity is a significant public health issue. Every year, a large number of hospitalizations are associated with exposure to extreme ambient temperatures, especially during heat waves and cold spells (Juopperi et al. 2002; Michelozzi et al. 2009; Schwartz et al. 2004; Semenza et al. 1999). For example, during the 1995 Chicago heat wave, it was estimated that there were 1,072 (11%) excess hospital admissions among all age groups, including 838 (35%) among those 65 years of age and older, with dehydration, heat stroke, and heat exhaustion as the main causes (Semenza et al. 1999). Actual numbers of morbidities may be greater than reported, because heat- or cold-related conditions may be listed as secondary diagnoses, and many studies have often considered primary diagnoses only (Kilbourne 1999; Semenza et al. 1999). Both heat- and cold-related morbidities occur more frequently among the elderly, as they are more vulnerable to temperature changes (Johnson et al. 2005; Knowlton et al. 2009; Kovats et al. 2004; Panagiotakos et al. 2004). In addition, urban residents may be exposed to higher temperatures than residents of surrounding suburban and rural areas because of the “heat island effect” resulting from high thermal absorption by dark paved surfaces and buildings, heat emitted from vehicles and air conditioners, lack of vegetation and trees, and poor ventilation (Barry and Chorley 2003; Hajat and Kosatsky 2009; O’Neill and Ebi 2009). Because of the urban heat island effect, people in urban areas are usually at an increased risk of morbidity from ambient heat exposure (O’Neill and Ebi 2009). The morbidity effect of temperature is likely to become more severe as the number of elderly people increases (from 737 million persons > 60 years old in 2009 to 2 billion by 2050 globally) and the proportion of urban residents increases (by approximately 18% over the next 40 years) and because climate change will continue for at least the next several decades, even under the most optimistic scenarios [IPCC 2007a; United Nations Department of Economic and Social Affairs (UNDESA) 2010a, 2010b].
In this paper, we assess the current epidemiological evidence concerning the effects of temperature on morbidity, identify knowledge gaps in this field, and make recommendations for future research directions.
The PubMed electronic database was used to retrieve published studies examining the relationship between ambient temperature and morbidity of noncommunicable diseases (we excluded communicable diseases such as vector-borne diseases, as the research designs and analysis methods differ between communicable and noncommunicable diseases). Our primary search used the following U.S. National Library of Medicine Medical Subject Headings (MeSH terms) and key words: weather, climate, temperature, morbidity, hospitalization, emergency medical services, family practice, primary health care, heat wave, cold surge, and cold spell. All subterms were included, and we limited the search to original epidemiological studies published in English before 30 June 2010.
To examine the relationship between ambient temperature and morbidity, all relevant studies were included in this review. Eligibility included any epidemiological studies that used original data and appropriate effect estimates [e.g., regression coefficient, relative risk (RR), odds ratio (OR), percent change in morbidity, and morbidity or excess morbidity after heat waves]; where ambient temperature or a composite temperature measure was a main exposure of interest; and where the outcome measure included a noncommunicable disease (e.g., cardiovascular, cerebrovascular, or respiratory diseases). Titles and abstracts were screened for relevance, and full texts were then obtained for further assessment if papers met the inclusion criteria. We also inspected the reference list of each article to check if any studies were missed from the primary electronic search.
A total of 614 articles were identified from the PubMed (National Library of Medicine 2010) database, and 76 initially met the eligibility criteria for full-text inspection after reading the abstracts (Figure 1). We excluded 41 articles because 3 had no original data, 27 assessed only the effect of season or broad weather conditions, and 11 did not report appropriate effect estimates. Five studies were added after manually inspecting the reference lists of all relevant articles. Finally, 40 articles were included in the review. Of these, 24 examined the relationship between general ambient temperature and morbidity, 15 investigated short-term effects of heat waves on morbidity, and 1 assessed both general ambient temperature-related and heat wave–related health effects.
Study designs and statistical approaches. A variety of study designs were used to assess the health effects of heat waves and cold spells and to characterize the association between temperature and morbidity. Most studies employed either a descriptive or time-series study design. Statistical methods varied with study design.
Descriptive studies. Simple comparisons were applied in the analysis of health effects of isolated heat waves in seven studies (Cerutti et al. 2006; Ellis et al. 1980; Johnson et al. 2005; Jones et al. 1982; Knowlton et al. 2009; Rydman et al. 1999; Semenza et al. 1999) in addition to studies where risk factors and illnesses studied during heat waves and cold spells were often characterized in details. To assess effects of heat waves on morbidity, most of the studies estimated an excess proportion by comparing observed versus expected morbidity. Many methods were used to calculate expected morbidity, which largely depended on the chosen baseline. Usually, expected hospital admissions were based on the average number of admissions during comparison days or weeks, for example, the days prior to or after a heat wave, or the same time period in previous years without heat waves (Huynen et al. 2001; Johnson et al. 2005; Semenza et al. 1999; Yang et al. 2009). Although such comparative analyses can provide useful insights into the short-term response of the population to a heat wave or cold spell event, they may underestimate or overestimate effects because of the use of an inappropriate baseline, potential morbidity displacement, and lack of control for confounding factors (e.g., air pollution).
Time-series studies. Time-series studies have been widely used to examine short-term effects of temperature on morbidity (Kovats et al. 2004; Linares and Diaz 2008; Michelozzi et al. 2009; Schwartz et al. 2004). Morbidity counts or rates were usually used as the outcome measures, whereas temperature measurements at corresponding intervals were employed as exposure indicators. Time-series analysis using daily data was commonly applied, but weekly or monthly data were used in some studies, which may make it difficult to detect acute temperature effects on morbidity (Roger and Francesca 2008; Touloumi et al. 2004). Effects were often estimated as the percent change in morbidity per unit increase (or decrease) in temperature (e.g., one or several degrees Centigrade or interquartile range change) (Ebi et al. 2004; Green et al. 2009; Koken et al. 2003; Lin et al. 2009). In this design, confounding is limited to time-varying factors such as air pollution, influenza epidemics, season, holiday (e.g., Christmas, New Year), and the day of the week (which could be taken into account in multivariable models).
In general, both hot and cold extremes of temperature have an adverse effect on health, which suggests a potential nonlinearity of the temperature effect. Thus, Poisson regression through generalized additive models (GAM) was widely used to assess the temperature–morbidity relationship after adjustment for long-term effects, seasonality, and other seasonally varying factors (Barnett et al. 2005; Ren et al. 2006; Schwartz et al. 2004). Alternatively, analyses were stratified by summer/winter or warm/cold periods to remove seasonal patterns and simplify analyses (Lin et al. 2009; Michelozzi et al. 2009; Piver et al. 1999; Wang et al. 2009; Ye et al. 2001). Appropriate temperature thresholds were selected based on model fit (Kovats et al. 2004) or selected cutoff (e.g., percentiles or absolute values of the temperature distribution) (Michelozzi et al. 2009), which facilitated the analysis of health effects of temperature extremes.
Exposure measurements. Mean daily temperature (Kovats et al. 2004; Liang et al. 2008; Schwartz et al. 2004) was a simple and common temperature indicator. Minimum (Ebi et al. 2004; Linares and Diaz 2008) and maximum temperatures (Linares and Diaz 2008; Wang et al. 2009) were also used in many studies. Diurnal temperature range was reported to be a risk factor for patients suffering from cardiovascular and respiratory diseases (Liang et al. 2008, 2009). Other studies used biometeorological indices such as apparent temperature (Green et al. 2009; Michelozzi et al. 2009) and Humidex (Mastrangelo et al. 2007). These perceived indices combine air temperature and humidity and are considered to be better measures of the effect of temperature on the human body than is temperature alone. However, no single temperature measure was reported to be superior to the others to predict the mortality (Barnett et al. 2010).
In examining the effect of heat waves (and cold spells), the first thing to be considered is the definition of the exposure, which may vary with geographic location and climatic condition because the sensitivity of populations to heat stress varies geographically (Hansen et al. 2008a; Knowlton et al. 2009; Kovats et al. 2004; Revich and Shaposhnikov 2008; Robinson 2001). As heat effects in one area may not be applicable to another area, multicity studies were recently conducted to assess general heat effects (Anderson and Bell 2009; Green et al. 2009; Michelozzi et al. 2009). Besides heat wave intensity, heat wave duration is also an important risk factor in estimating the health effect of heat episodes (Mastrangelo et al. 2007). Vulnerability to heat stress depends on many factors, such as age, preexisting diseases, environmental humidity, and adaptative response (Bouchama and Knochel 2002; Cui et al. 2005; Parsons 2003). A long heat wave could lead to accumulated heat stress on the body when heat produced and obtained from the environment overwhelms the heat loss by thermoregulation. Over consecutive hot days without cooler nights, individuals may suffer from thermoregulatory failure, increasing the risk of illnesses (Bouchama and Knochel 2002; Parsons 2003). There is also evidence that the effect of extreme cold might increase with increasing duration, as low temperature can lead to cardiovascular stress by increasing platelet counts, red cells, blood viscosity, plasma cholesterol, fibrinogen, and blood pressure and increase susceptibility to pulmonary diseases by causing bronchoconstriction (Hong et al. 2003; Huynen et al. 2001; Keatinge et al. 1984; Mercer 2003).
Outcome measurements. Although admissions for some heat-related conditions such as heat stroke, heat exhaustion, fluid and electrolyte abnormalities, and acute renal failure were higher during heat waves (Hansen et al. 2008b; Knowlton et al. 2009; Semenza et al. 1999), actual numbers were assumed to be underestimated, as many cases were likely to be coded cardiovascular or respiratory diseases in primary diagnoses. As a result, some researchers recommend that primary and secondary discharge diagnoses be considered together to reduce misclassification of heat-related diseases (Kilbourne 1999; Semenza et al. 1999). The common causes of morbidity evaluated in previous studies included total cardiovascular and respiratory diseases (Lin et al. 2009; Linares and Diaz 2008; Michelozzi et al. 2009; Ren et al. 2006) and specific diseases such as stroke (Kyobutungi et al. 2005; Ohshige et al. 2006; Wang et al. 2009), acute myocardial infarction (Chang et al. 2004; Ebi et al. 2004; Schwartz et al. 2004; Ye et al. 2001), and acute coronary syndrome (ACS; Liang et al. 2008; Panagiotakos et al. 2004).
Some direct cold injuries occur during winter, such as frostbite and hypothermia (Hassi et al. 2005; Juopperi et al. 2002). Ischemic stoke (Hong et al. 2003), coronary events (Barnett et al. 2005), and cardiovascular and respiratory diseases (Hajat et al. 2004; Hajat and Haines 2002) were reported in the studies of cold temperature morbidity. No study has investigated the morbidity after a cold spell, whereas only a few studies examined cardiovascular and respiratory mortality of extreme cold temperatures (Huynen et al. 2001; Kysely et al. 2009; Revich and Shaposhnikov 2008).
A number of studies examined the relationship between ambient temperature and morbidity. These studies identified the general risks of temperature as well as temperature extremes in multiple areas over time, using different research designs. Table 1 summarizes the findings of ambient temperature–morbidity studies, whereas Table 2 summarizes the findings of heat wave studies.
Threshold effects of temperature. A nonlinear relationship between temperature and morbidity was evident across different studies that illustrated U-, V-, or J-shaped patterns (Kovats et al. 2004; Liang et al. 2008; Lin et al. 2009; Linares and Diaz 2008), with the minimum morbidity at a certain temperature or temperature range (threshold temperature) and increased morbidity below and above the threshold. However, few studies identified clear threshold temperatures based on model fit (Kovats et al. 2004; Lin et al. 2009).
There is some evidence that both hot and cold threshold temperature for morbidity vary by location. For example, in a study in New York City, hospital admissions for respiratory diseases increased at temperatures > 28.9°C (Lin et al. 2009). However, the threshold temperature of respiratory hospital admissions in London, United Kingdom, was lower (23°C) (Kovats et al. 2004), as the cooler summers resulted in lower acclimatization to high temperature. The cold threshold temperature also differed for each region in Quebec, Canada, in winter (Bayentin et al. 2010).
Different thresholds have also been identified for different diseases. A large increase in emergency hospital admissions was observed for respiratory diseases at temperatures > 23°C in Greater London, whereas admissions for renal diseases increased above a lower temperature of 18°C (Kovats et al. 2004).
Magnitude of the effects of temperature and heat wave. Consistent with expectations that the relation between temperature and morbidity will follow a V- or J-shaped curve, a study in Taiwan reported that emergency room admissions for acute ACS were lowest for temperatures of 27–29°C. Compared with this baseline range, ACS admissions were 28.4% higher for average daily temperatures in the range of 17–27°C (with a slight increase > 29°C) and 53.9% higher for temperatures < 17°C (Liang et al. 2008). To fully assess the shape of the association between temperature and morbidity, it is necessary to evaluate associations across the entire temperature range throughout a year. Studies focused on associations during hot or cold seasons only usually show a linear association of temperature with morbidity. For example, Lin et al. (2009) reported increased counts of cardiovascular [3.6%; 95% confidence interval (CI): 0.3, 6.9] and respiratory diseases (2.7%; 95% CI: 1.3, 4.2) with a 1°C increase in temperature during the summer in New York City, whereas a study in Brisbane reported a decreased risk of emergency admissions for primary intracerebral hemorrhage with a 1°C increase in minimum temperature (RR = 0.95; 95% CI: 0.91, 0.98) during the winter (Wang et al. 2009). In contrast, a study of 12 European cities revealed that the association between temperature and cardiovascular and cerebrovascular hospital admissions tended to be negatively linear but did not reach statistical significance during hot seasons (Michelozzi et al. 2009). However, some studies that evaluated associations over the entire year also reported evidence of linear versus J- or V-shaped associations (Panagiotakos et al. 2004; Schwartz et al. 2004). For example, in 12 U.S. cities, average temperature was positively related to hospital admissions for heart diseases among adults ≥ 65 years old (Schwartz et al. 2004). Cardiovascular, respiratory, and cerebrovascular diseases comprise many subtypes that might react to temperature in different ways (Dawson et al. 2008; Lin et al. 2009; Wang et al. 2009; Ye et al. 2001). For example, hemorrhage stroke and ischemic stroke hospital admissions, both of which would be classified as cerebrovascular diseases, showed opposite relationships to temperature increases in California (Green et al. 2009). Additionally, an interquartile range increase in maximum temperature during hot seasons in Denver, Colorado, was associated with a 12.5% and 28.3% decrease in risk of hospitalization for coronary atherosclerosis and pulmonary heart disease, respectively, compared with a 17.5% increase for acute myocardial infarction among the elderly (Koken et al. 2003). These results suggested that patients with chronic rather than acute cardiovascular conditions might avoid outdoor exposures during unfavorable weather, resulting in a null or negative association. Moreover, if appointments for mild diseases are postponed or cancelled during extremely hot or cold periods, the effect of temperature on morbidity might be underestimated.
Despite evidence of variation among specific diseases, increased overall morbidity has been consistently associated with heat waves. For example, during a Chicago, Illinois, heat wave in 1995, there were 838 (35%) more hospital admissions of the elderly (≥ 65 years old) compared with the average number of admissions during comparable weeks (Semenza et al. 1999). A total of 16,166 (3%) excess emergency department visits and 1,182 (1%) excess hospitalizations occurred in California during the 2006 heat wave (Knowlton et al. 2009). In England, the 2003 heat wave caused an excess of 1% total emergency hospital admissions (Johnson et al. 2005). In a study in Adelaide, Australia, Nitschke et al. (2007) reported a 4% and 7% increase in total ambulance transport and hospital admissions during heat waves, respectively, compared with non–heat wave periods.
Lag structure of temperature. Some studies explored temporal patterns (lag structure) of the association between exposure to temperature over previous days and health risk on a particular day. Various lag days were reported for the association of temperature with morbidity, ranging from the same day (Green et al. 2009) to 1 month (Chang et al. 2004), with shorter lags during warmer seasons and longer lags during cooler seasons (Barnett et al. 2005; Hajat and Haines 2002). In a study of 12 U.S. cities, Schwartz et al. (2004) also reported that associations with hot temperatures were more immediate than with cold temperatures. Most recent studies have reported short-term effects of high temperature on the same day and the 3 days after heat exposure (Green et al. 2009; Koken et al. 2003; Lin et al. 2009). For example, Lin et al. (2009) observed that the greatest number of hospital admissions for respiratory and cardiovascular diseases was 0–1 days and 1–3 days after increased temperatures (Lin et al. 2009). Seven-day lag was used to evaluate the effect of temperature on hospital admissions for several specific cardiovascular diseases (Ebi et al. 2004). One-month lag has also been reported by a study that evaluated average temperatures over a monthly period across several whole years (Chang et al. 2004), but it was not clear whether the effects would have been more immediate if daily data had been evaluated. Hajat and Haines (2002) found a strong association between consultations for respiratory disease and mean temperature < 5°C over a 10-day period (i.e., 6–15 days before the consultation) in London, which implied a later and longer lag for cold temperatures than hot ones.
Harvesting effects of temperature. Evidence of a harvesting effect (e.g., mortality displacement) has been documented by studies of heat-related mortality (Braga et al. 2002; Muggeo and Hajat 2009) that showed an immediate increase in mortality followed by reduced mortality among susceptible people, consistent with a temporal advance in deaths that would have occurred later in time in the absence of exposure to heat or cold. However, the impact of harvesting on morbidity has not been fully investigated, and short-, intermediate-, and long-term effects should be examined to determine the impact of harvesting. Schwartz et al. (2004) reported evidence of a short-term advance in emergency hospital admissions for heart diseases and myocardial infarction among people ≥ 65 years of age within a few days after high-temperature exposure, with a positive association on the day of admission followed by a period of lower-than-average admissions, returning to the baseline after a week. No evidence of a harvesting effect was observed for cold weather in this study (Schwartz et al. 2004). No other temperature–morbidity studies have formally investigated the harvesting issue.
Confounding and modification of the temperature–morbidity relationship. Some sociodemographic factors might confound and modify the temperature–morbidity relationship. Children and the elderly are usually susceptible to heat- or cold-related health risks. Although there was evidence for heat-related increases in emergency admissions for children < 5 years of age (Kovats et al. 2004), more studies reported the highest-risk age groups to be those > 65 years (Hong et al. 2003; Knowlton et al. 2009; Semenza et al. 1999) or 75 years of age (Johnson et al. 2005; Kovats et al. 2004; Lin et al. 2009). Women have been reported to have a greater risk for coronary events, ACS, and ischemic stroke in cold periods than do men (Barnett et al. 2005; Hong et al. 2003; Panagiotakos et al. 2004). However, emergency transport cases for heat stroke, cardiac insufficiency, hypertension, myocardial infarction, asthma, chronic bronchitis, and pneumonia were greater for males than for females during the summer in Tokyo (Piver et al. 1999; Ye et al. 2001). Lin et al (2009) reported a higher risk of being admitted to hospital for respiratory diseases during the summer in New York for people of Hispanic ethnicity than for those of non-Hispanic ethnicity (6.1% vs. 1.7%), whereas no effect modification by race/ethnicity (e.g., white, black, Hispanic, Asian) or sex was found in the association between mean apparent temperature and hospital admissions for cardiovascular and respiratory diseases in California (Green et al. 2009).
In many locations, concentrations of air pollutants are associated with meteorological conditions. For example, there is usually a higher ozone concentration in summer, as it is a secondary pollutant caused by the reaction of volatile organic compounds, carbon monoxide, and nitrogen dioxide in the presence of sunlight, whereas particulate matter < 10 µm in aerodynamic diameter (PM10) peaks during the winter in many places because of the combustion of coal and/or wood for heating. These pollutants are often controlled for when considering the effect of ambient temperature on morbidity (Kovats et al. 2004; Liang et al. 2008; Linares and Diaz 2008; Michelozzi et al. 2009). However, few studies have explored whether exposure to air pollution modifies associations between temperature and morbidity. Ren et al. (2006) reported that PM10 significantly modified the relationship between daily minimum temperature and hospital admissions for cardiovascular and respiratory diseases in Brisbane, Australia, with stronger estimated effects of temperature at higher levels of PM10. In a multicity European study, ozone did not appear to modify or confound associations between hot temperature and hospital admissions for cardiovascular, cerebrovascular, and respiratory diseases (Michelozzi et al. 2009).
Conclusions and Recommendations
We identified 40 relevant studies, most conducted in the United States and Europe during the last decade. Some descriptive studies provided early evidence of heat-related morbidity in specific cities during a single heat wave, and research has expanded recently to address the temperature–morbidity relationship in larger and more diverse populations in multiple areas. Although the case-crossover approach has seldom been used (Green et al. 2009; Hong et al. 2003; Kyobutungi et al. 2005), it is expected to be increasingly applied because of its ability to effectively control for individual-level confounding.
A number of well-controlled studies showed that ambient temperature was significantly associated with total and cause-specific morbidities, in which most reported heat effects with only a few reporting cold effects. Several studies found U- or V-shaped exposure–response relationships, with morbidity increasing at both ends of the temperature scale. The majority of studies reported detrimental effects of heat on the same day or up to the following 3 days, and longer cold effects up to a 2- to 3-week lag, with no substantial effects after more than 1 month.
A number of reasons may explain the heterogeneity of results across these studies. First, previous studies covered a wide range of populations in various geographical locations. Besides different demographic characteristics, some domestic and local adaptation factors could influence the direction and magnitude of the effects of ambient temperature on nonfatal health outcomes. For example, Ostro et al. (2010) estimated that the use of air conditioning could significantly reduce the effects of temperature on hospitalizations for multiple diseases, with 0.76% absolute reduction in excess risk of cardiovascular disease for every 10% increase in air conditioner ownership. Second, many temperature indicators have been used to define exposure, including minimum, mean, maximum temperature, diurnal temperature range, apparent temperature, and Humidex. However, which temperature measure is better to predict morbidity remains to be determined. Third, studies have evaluated different measures of morbidity, including general practitioner visits (Hajat et al. 2004; Hajat and Haines 2002), emergency department visits or admissions (Liang et al. 2009; Wang et al. 2009), and hospitalizations (Lin et al. 2009; Michelozzi et al. 2009). They are not mutually exclusive (e.g., a patient visiting an emergency department could be subsequently admitted to the hospital). Emergency is typically considered to be less severe and more acute than hospitalization, which implies that it can catch the effect of temperature change at the early stage. It has been suggested that studies including emergency department visits may yield more valuable information for describing the epidemiology of temperature-related morbidity than a hospitalization-only study (Knowlton et al. 2009). Finally, there were also many methodological differences across studies, including statistical models, study population characteristics (e.g., age and sex), use of lag days (e.g., a single lag and multiple lag), and potential confounders considered.
The IPCC has projected that global mean surface temperature will increase by 1.8–4.0°C (best estimate) by 2100 relative to 1980–1999 (IPCC 2007a). Therefore, efforts to understand how climate change will affect health are urgently needed. Further studies are warranted to determine appropriate measures of exposure for morbidity research; to estimate nonlinear delayed temperature effects; to investigate the threshold temperatures in specific locations; and to understand the relative importance and interactive effects of air pollutants and temperature on morbidity, especially in areas with high air pollution. More multicity studies with consistent methodology should be conducted to make it easy to compare and interpret the temperature effects on morbidity across cities. There is also a need to consider more than one type of morbidity and to track cases from one health service to another by linking medical records. Such studies will provide valuable information for designing and implementing intervention strategies to alleviate the public health impacts of climate change.
- Anderson BG, Bell ML. 2009. Weather-related mortality: how heat, cold, and heat waves affect mortality in the United States. Epidemiology 20:205–213.
- Applegate WB, Runyan JW Jr, Brasfield L, Williams ML, Konigsberg C, Fouche C. 1981. Analysis of the 1980 heat wave in Memphis. J Am Geriatr Soc 29:337–342.
- Barnett AG, Dobson AJ, McElduff P, Salomaa V, Kuulasmaa K, Sans S. 2005. Cold periods and coronary events: an analysis of populations worldwide. J Epidemiol Community Health 59:551–557.
- Barnett AG, Tong S, Clements AC. 2010. What measure of temperature is the best predictor of mortality? Environ Res 110:604–611.
- Barry RG, Chorley RJ 2003. Atmosphere, Weather and Climate. 8th ed. New York:Methuen & Co. Ltd.
- Bayentin L, El Adlouni S, Ouarda TB, Gosselin P, Doyon B, Chebana F. 2010. Spatial variability of climate effects on ischemic heart disease hospitalization rates for the period 1989–2006 in Quebec, Canada. Int J Health Geogr 9:5.; doi:10.1186/1476-072X-9-5 [Online 8 February 2010]
- Bouchama A, Knochel JP. 2002. Heat stroke. N Engl J Med 346:1978–1988.
- Braga AL, Zanobetti A, Schwartz J. 2002. The effect of weather on respiratory and cardiovascular deaths in 12 U.S. cities. Environ Health Perspect 110:859–863.
- Cerutti B, Tereanu C, Domenighetti G, Cantoni E, Gaia M, Bolgiani I, et al. 2006. Temperature related mortality and ambulance service interventions during the heat waves of 2003 in Ticino (Switzerland). Soz Praventivmed 51:185–193.
- Chang CL, Shipley M, Marmot M, Poulter N. 2004. Lower ambient temperature was associated with an increased risk of hospitalization for stroke and acute myocardial infarction in young women. J Clin Epidemiol 57:749–757.
- Cui J, Arbab-Zadeh A, Prasad A, Durand S, Levine BD, Crandall CG. 2005. Effects of heat stress on thermoregulatory responses in congestive heart failure patients. Circulation 112:2286–2292.
- Dawson J, Weir C, Wright F, Bryden C, Aslanyan S, Lees K, et al. 2008. Associations between meteorological variables and acute stroke hospital admissions in the west of Scotland. Acta Neurol Scand 117:85–89.
- Ebi KL, Exuzides KA, Lau E, Kelsh M, Barnston A. 2004. Weather changes associated with hospitalizations for cardiovascular diseases and stroke in California, 1983–1998. Int J Biometeorol 49:48–58.
- Ellis FP, Prince HP, Lovatt G, Whittington RM. 1980. Mortality and morbidity in Birmingham during the 1976 heatwave. Q J Med 49:1–8.
- Faunt JD, Wilkinson TJ, Aplin P, Henschke P, Webb M, Penhall RK. 1995. The effete in the heat: heat-related hospital presentations during a ten day heat wave. Aust N Z J Med 25:117–121.
- Green RS, Basu R, Malig B, Broadwin R, Kim JJ, Ostro B. 2009. The effect of temperature on hospital admissions in nine California counties. Int J Public Health 55:113–121.
- Hajat S, Bird W, Haines A.. 2004. Cold weather and GP consultations for respiratory conditions by elderly people in 16 locations in the U.K. Eur J Epidemiol 19:959–968.
- Hajat S, Haines A.. 2002. Associations of cold temperatures with GP consultations for respiratory and cardiovascular disease amongst the elderly in London. Int J Epidemiol 31:825–830.
- Hajat S, Kosatsky T.. 2009. Heat-related mortality: a review and exploration of heterogeneity. J Epidemiol Community Health. ; doi:10.1136/jech.2009.087999 [Online 19 August 2009]
- Hansen AL, Bi P, Nitschke M, Ryan P, Pisaniello D, Tucker G. 2008a. The effect of heat waves on mental health in a temperate Australian city. Environ Health Perspect 116:1369–1375.
- Hansen AL, Bi P, Ryan P, Nitschke M, Pisaniello D, Tucker G. 2008b. The effect of heat waves on hospital admissions for renal disease in a temperate city of Australia. Int J Epidemiol 37:1359–1365.
- Hassi J, Rytkonen M, Kotaniemi J, Rintamaki H.. 2005. Impacts of cold climate on human heat balance, performance and health in circumpolar areas. Int J Circumpolar Health 64:459–467.
- Hong YC, Rha JH, Lee JT, Ha EH, Kwon HJ, Kim H. 2003. Ischemic stroke associated with decrease in temperature. Epidemiology 14:473–478.
- Huynen MM, Martens P, Schram D, Weijenberg MP, Kunst AE. 2001. The impact of heat waves and cold spells on mortality rates in the Dutch population. Environ Health Perspect 109:463–470.
- IPCC (Intergovernmental Panel on Climate Change) 2007a. Climate Change 2007.: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Geneva:Intergovernmental Panel on Climate Change.
- IPCC (Intergovernmental Panel on Climate Change) 2007b. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK:Cambridge University Press.
- Johnson H, Kovats RS, McGregor G, Stedman J, Gibbs M, Walton H, et al. 2005. The impact of the 2003 heat wave on mortality and hospital admissions in England. Health Stat Q 25:6–11.
- Jones TS, Liang AP, Kilbourne EM, Griffin MR, Patriarca PA, Wassilak SG, et al. 1982. Morbidity and mortality associated with the July 1980 heat wave in St Louis and Kansas City, MO. JAMA 247:3327–3331.
- Juopperi K, Hassi J, Ervasti O, Drebs A, Nayha S.. 2002. Incidence of frostbite and ambient temperature in Finland, 1986–1995. A national study based on hospital admissions. Int J Circumpolar Health 61:352–362.
- Keatinge WR, Coleshaw SR, Cotter F, Mattock M, Murphy M, Chelliah R. 1984. Increases in platelet and red cell counts, blood viscosity, and arterial pressure during mild surface cooling: factors in mortality from coronary and cerebral thrombosis in winter. Br Med J (Clin Res Ed) 289:1405–1408.
- Kilbourne EM. 1999. The spectrum of illness during heat waves. Am J Prev Med 16:359–360.
- Knowlton K, Rotkin-Ellman M, King G, Margolis HG, Smith D, Solomon G, et al. 2009. The 2006 California heat wave: impacts on hospitalizations and emergency department visits. Environ Health Perspect 117:61–67.
- Koken PJ, Piver WT, Ye F, Elixhauser A, Olsen LM, Portier CJ. 2003. Temperature, air pollution, and hospitalization for cardiovascular diseases among elderly people in Denver. Environ Health Perspect 111:1312–1317.
- Kovats RS, Hajat S, Wilkinson P. 2004. Contrasting patterns of mortality and hospital admissions during hot weather and heat waves in Greater London, U.K. Occup Environ Med 61:893–898.
- Kyobutungi C, Grau A, Stieglbauer G, Becher H.. 2005. Absolute temperature, temperature changes and stroke risk: a case-crossover study. Eur J Epidemiol 20:693–698.
- Kysely J, Pokorna L, Kyncl J, Kriz B.. 2009. Excess cardiovascular mortality associated with cold spells in the Czech Republic. BMC Public Health 9:19.; doi:10.1186/1471-2458-9-19 [Online 15 January 2009]
- Larrieu S, Carcaillon L, Lefranc A, Helmer C, Dartigues J-F, Tavernier B, et al. 2008. Factors associated with morbidity during the 2003 heat wave in two population-based cohorts of elderly subjects: PAQUID and Three City. Eur J Epidemiol 23:295–302.
- Liang WM, Liu WP, Chou SY, Kuo HW. 2008. Ambient temperature and emergency room admissions for acute coronary syndrome in Taiwan. Int J Biometeorol 52:223–229.
- Liang WM, Liu WP, Kuo HW. 2009. Diurnal temperature range and emergency room admissions for chronic obstructive pulmonary disease in Taiwan. Int J Biometeorol 53:17–23.
- Lin S, Luo M, Walker RJ, Liu X, Hwang SA, Chinery R. 2009. Extreme high temperatures and hospital admissions for respiratory and cardiovascular diseases. Epidemiology 20:738–746.
- Linares C, Diaz J.. 2008. Impact of high temperatures on hospital admissions: comparative analysis with previous studies about mortality (Madrid). Eur J Public Health 18:317–322.
- Mastrangelo G, Fedeli U, Visentin C, Milan G, Fadda E, Spolaore P.. 2007. Pattern and determinants of hospitalization during heat waves: an ecologic study. BMC Public Health 7:200.; doi:10.1186/1471-2458-7-200 [Online 9 August 2007]
- Mercer JB. 2003. Cold—an underrated risk factor for health. Environ Res 92:8–13.
- Michelozzi P, Accetta G, De Sario M, D’Ippoliti D, Marino C, Baccini M, et al. 2009. High temperature and hospitalizations for cardiovascular and respiratory causes in 12 European cities. Am J Respir Crit Care Med 179:383–389.
- Muggeo VM, Hajat S. 2009. Modelling the nonlinear multiple-lag effects of ambient temperature on mortality in Santiago and Palermo: a constrained segmented distributed lag approach. Occup Environ Med 66:584–591.
- National Climate Centre 2009. The exceptional January-February 2009 heatwave in southeastern Australia, Bureau of Meteorology, Special Climate Statement 17. Melbourne, Australia:Bureau of Meteorology.
- National Library of Medicine 2010. PubMed. Available: http://www.ncbi.nlm.nih.gov/pubmed/ [accessed 8 July 2010]
- Nitschke M, Tucker GR, Bi P. 2007. Morbidity and mortality during heatwaves in metropolitan Adelaide. Med J Aust 187:662–665.
- Oberlin M, Tubery M, Cances-Lauwers V, Ecoiffier M, Lauque D.. 2010. Heat-related illnesses during the 2003 heat wave in an emergency service. Emerg Med J 27:297–299.
- Ohshige K, Hori Y, Tochikubo O, Sugiyama M.. 2006. Influence of weather on emergency transport events coded as stroke: population-based study in Japan. Int J Biometeorol 50:305–311.
- O’Neill MS, Ebi KL. 2009. Temperature extremes and health: impacts of climate variability and change in the United States. J Occup Environ Med 51:13–25.
- Ostro B, Rauch S, Green R, Malig B, Basu R.. 2010. The effects of temperature and use of air conditioning on hospitalizations. Am J Epidemiol 172:1053–1061.
- Panagiotakos DB, Chrysohoou C, Pitsavos C, Nastos P, Anadiotis A, Tentolouris C, et al. 2004. Climatological variations in daily hospital admissions for acute coronary syndromes. Int J Cardiol 94:229–233.
- Parsons K 2003. Human Thermal Environments: The Effects of Hot, Moderate and Cold Environments on Human Health, Comfort and Performance. London and New York:Taylor & Francis.
- Pattenden S, Nikiforov B, Armstrong BG. 2003. Mortality and temperature in Sofia and London. J Epidemiol Community Health 57:628–633.
- Piver WT, Ando M, Ye F, Portier CJ. 1999. Temperature and air pollution as risk factors for heat stroke in Tokyo, July and August 1980–1995. Environ Health Perspect 107:911–916.
- Ren C, Williams GM, Tong S. 2006. Does particulate matter modify the association between temperature and cardiorespiratory diseases? Environ Health Perspect 114:1690–1696.
- Revich B, Shaposhnikov D.. 2008. Excess mortality during heat waves and cold spells in Moscow, Russia. Occup Environ Med 65:691–696.
- Robinson PJ. 2001. On the definition of a heat wave. J Appl Meteorol 40:762–775.
- Roger P, Francesca D 2008. Statistical Methods for Environmental Epidemiology with R: A Case Study in Air Pollution and Health. New York:Springer.
- Rydman RJ, Rumoro DP, Silva JC, Hogan TM, Kampe LM. 1999. The rate and risk of heat-related illness in hospital emergency departments during the 1995 Chicago heat disaster. J Med Syst 23:41–56.
- Schwartz J, Samet JM, Patz JA. 2004. Hospital admissions for heart disease: the effects of temperature and humidity. Epidemiology 15:755–761.
- Semenza JC, McCullough JE, Flanders WD, McGeehin MA, Lumpkin JR. 1999. Excess hospital admissions during the July 1995 heat wave in Chicago. Am J Prev Med 16:269–277.
- Touloumi G, Atkinson R, Tertre AL, Samoli E, Schwartz J, Schindler C, et al. 2004. Analysis of health outcome time series data in epidemiological studies. Environmetrics 15:101–117.
- UNDESA (United Nations Department of Economic and Social Affairs) 2010a. World Population Ageing. New York:United Nations Department of Economic and Social Affairs.
- UNDESA (United Nations Department of Economic and Social Affairs) 2010b. World Urbanization Prospects: The 2009 Revision. New York:United Nations Department of Economic and Social Affairs Population Division.
- Wang XY, Barnett AG, Hu W, Tong S. 2009. Temperature variation and emergency hospital admissions for stroke in Brisbane, Australia, 1996–2005. Int J Biometeorol 53:535–541.
- WHO (World Health Organization) 2008. Protecting Health from Climate Change—World Health Day 2008. Geneva:World Health Organization.
- Yang TC, Wu PC, Chen VY, Su HJ. 2009. Cold surge: a sudden and spatially varying threat to health? Sci Total Environ 407:3421–3424.
- Ye F, Piver WT, Ando M, Portier CJ. 2001. Effects of temperature and air pollutants on cardiovascular and respiratory diseases for males and females older than 65 years of age in Tokyo, July and August 1980–1995. Environ Health Perspect 109:355–359.
New Impact Factor
We are pleased to announce our new impact factor of 7.03 and—for the first time—our inclusion in the category of Toxicology. Thank you to our authors and readers, who continue to make EHP a leading journal in Environmental Sciences, in Public, Environmental, and Occupational Health, and now in Toxicology.
EHP News Feature Wins Award
Our March 2013 cover story, “A Tale of Two Forests: Addressing Postnuclear Radiation at Chernobyl and Fukushima,” has won first place in the Outstanding Feature Story category of the Society of Environmental Journalists Awards for Reporting on the Environment. The judges called the story “an exceedingly vital and original piece of environmental feature writing.” Congratulations to authors Winifred A. Bird and Jane Braxton Little on their exciting achievement!
CEHN August 2014 Article of the Month
“Gestational Exposure to Endocrine-Disrupting Chemicals and Reciprocal Social, Repetitive and Stereotypic Behaviors in 4- and 5-Year-Old Children: The HOME Study” (Environ Health Perspect; DOI:10.1289/ehp.1307261) has been selected by the Children’s Environmental Health Network (CEHN) as its August 2014 Article of the Month. These CEHN summaries discuss the potential policy implications of current children’s environmental health research.
Register Today for PPTOX IVEnvironmental Stressors in Disease and Implications for Human Health
October 26–29, 2014
Boston Marriott Long Wharf Hotel
Join the Endocrine Society for the fourth international summit of Prenatal Programming and Toxicity (PPTOX), a premiere conference series dedicated to cutting-edge discussion of environmental hazards during early life and long-term consequences.Key deadlines:
* Abstract submission: Tuesday, September 2
* Housing deadline: Monday, October 6
For more information, visit the Endocrine Society website.
Sign Up to Receive E-mail Alerts
Recent Advance Publications
- Effect of Exposure to Atmospheric Ultrafine Particles on Production of Free Fatty Acids and Lipid Metabolites in the Mouse Small Intestine
- Risks and Benefits of Green Spaces for Children: A Cross-Sectional Study of Associations with Sedentary Behavior, Obesity, Asthma, and Allergy
- Genistein Disrupts Glucocorticoid Receptor Signaling in Human Uterine Endometrial Ishikawa Cells
- Modification of the Association between PM10 and Lung Function Decline by Cadherin 13 Polymorphisms in the SAPALDIA Cohort: A Genome-Wide Interaction Analysis
- Mitochondria, Energetics, Epigenetics, and Cellular Responses to Stress
- Incense Use and Cardiovascular Mortality among Chinese in Singapore: The Singapore Chinese Health Study
- Perfluorochemicals and Human Semen Quality: The LIFE Study
- AdvPubl: Atmospheric ultrafine particles and intestinal lipid metabolism http://t.co/flqRKKLMep
- Trending EHP news this month: Nanosilver: weighing the risks and benefits http://t.co/6oSYgL8MNO
- Trending EHP research this month: The societal costs and benefits of commuter bicycling http://t.co/yGlks7cL5l
- EHPNoonNews: Big Food to divulge chemical info http://t.co/jaCI6PWQRx @washingtonpost EHP lookback http://t.co/1eRkamlSkF
- EHPNoonNews: EPA identifies health concern from chemical used in paint strippers http://t.co/yMIisVom4Y @epa