39

Impact Assessment of Heat Stress on Population Health inJapan and China
Shinji ASANUMA1, Chaoke LIANG2 and Mitsuru ANDO3*
1

Japan Institute of Rural Medicine, Saku, Nagano 384-0301, Japan
National Institute for Environmental Health and Related Product Safety,
Chinese Center for Disease Control and Prevention, Beijing 100050, China
3
Toyama University of International Studies, Toyama 930-1292, Japane-mail: mitsuruando@hotmail.com*corresponding author
2

Abstract
In accordance with the rapid increase in greenhouse gas emissions, climate models predict an increase in the global surface temperature in the future. With regard to human health, it is thought that
global warming may have a critical impact due to increased heat stress in summer. Furthermore, enormous population growth is accelerating the heat island phenomenon in urban areas. Since global warming and the heat island phenomenon will increase heat stress in summer in communities, this paper
examines population health risks caused by heat stress.
An epidemiological survey showed the incidence of heat-related illness to be significantly correlated to high temperatures in Japan and China. The incidence of heat-related illness in populations especially among the elderly increased exponentially with rising maximum daily temperatures in summer.
The incidence of heat-related illness increased in the daytime when the maximum daily temperature andthe heat index temperature in summer rose above the threshold temperature. The incidence of pneumonia was correlated with cold temperatures in winter and hot temperatures in summer. Therefore, it isnecessary to study age- and gender-dependent health damage of populations in local communities under
extreme heat stress in hot environments.
To evaluate the age-related response of populations against health damage from hot temperatures,
we studied the biomedical response of animals to heat stress. Conditions of hyperthermia caused byexposure to hot environments resulted in marked damage to some essential organs in animals. Damage
from heat-stress-inducible oxygen free radicals becomes more severe in aged animals. Since aging andhyperthermia have a synergistic effect on peroxidative damage, it is essential to have protective enzyme
activities against oxygen free radicals.
To prevent health impacts from heat stress in populations due to global warming and the heatisland phenomenon, it will be necessary to improve environment design in urban and rural areas and topromote population health in aged persons in the world.
Key words: free radical, heat island, heat stress, heat stroke, pneumonia

1. Introduction
In accordance with the rapid increase in greenhouse gas emissions through anthropogenic fuel burning, climate models predict an increase in the global
mean temperature of 0.8°C - 2.6°C and 1.4°C - 5.8°C
by the years 2050 and 2100, respectively (IPCC,
2001a). Global warming appears to be strongly linked
to increased population globally and economic growth
in recent decades (IPCC, 2000).
Reports by the Intergovernmental Panel on Climate
Change (IPCC) indicate that one of the most imporGlobal Environmental Research
11: 39-44 (2007)
printed in Japantant direct impacts of global warming may be a greater
frequency and greater duration of exposure to hot temperatures, especially during the summer months(IPCC, 2001b). Populations at risk including aged
persons should be facing health impacts of climatechange (McMichael et al., 1996; Ando, 1998).
Typical hyperthermia in humans sometimes occurs
in cases of severe heat stress in summer or as a resultof hard exercise regardless of location throughout theworld. In some large cities in temperate regions,extreme heat stress is associated with an enhanced
heat island effect (Hawkins-Bell & Rankin, 1994;©2007 AIRIES40

S. ASANUMA et al.

Donoghue et al., 1995; Hales et al., 1996). The
heat-related morbidity and mortality from factors suchas the incidence of heat stroke in aged persons has
been shown to increase as a result of exposure to extremely hot temperatures in summer (Kalkstein, 1994;
Ando et al., 1996; Piver et al., 1999; Vandentorren
et al., 2004). Heat stroke, heat cramps and heatexhaustion are caused by severe hyperthermia, andbody temperatures of typical patients exceed 40°C.
Many organs such as the liver, kidney and central
nervous system are damaged by severe hyperthermia
and thrombus infarcts, and death from heat stroke may
be caused by injury to these organs (Hales & Richards,
1987; Ando et al., 1997).
Since heat stress is an important risk factor inglobal warming and the heat island phenomenon, it isnecessary to evaluate the health impacts of heat stresson human and animal populations.

2. Materials and Methods
2.1 Epidemiological research
Epidemiological research was carried out in Tokyo,
Japan, and Wuhan, China, to evaluate the health risksof populations to heat stress in hot and humid summers in the Asian monsoon region. The populations ofthese cities are 12.8 million and 4.8 million residents,
respectively. The monthly mean temperature of thehottest month during the past 30 years was 27.1°C in
August in Tokyo and 28.6°C in July in Wuhan. The
monthly average relative humidity during thesemonths was 73% in Tokyo and 79% in Wuhan, respectively.
The patients in this study were analyzed using
emergency transportation records in Tokyo andWuhan as a database. Furthermore to analyze the relationship between heat-related illness and temperature,heat-related illness data in these cities have been calculated according to gender and age.
A longitudinal epidemiological study concerning
the relationship between hot summer weather andheat-related illness was carried out. The present study
was summarized for high temperature and heat-related
illness in Tokyo, Japan, and Wuhan, China, during
1980 to 1995 and 1996 to 2002, respectively.
2.2 Model experiment
For impact assessment using an experimental
model expressing the relationship between heat stressand aging, SPF-grade 5-week-old male Fisher rats
were housed in 25±0.5°C under a 12-h light and 12-hdark cycle. Rats at 7 weeks, 12 months, 17 months
and 25 months in age, were randomly divided andkept in rooms at 25±0.5°C, 30±0.5°C, 32±0.5°C and
35±0.5°C at a relative humidity of 40±10% for periods of 3 to 42 days. After exposure to various environmental temperatures, animals were sacrificed between
10:00 and 12:00 a.m. by severing the main abdominal
artery while under ether anesthesia. Tissue and organcell samples were prepared for biochemical analysis
for various enzyme activities.
2.3 Statistical evaluation
Statistical analyses were carried out using the F
and t-test of Snedecor and Cochran (1967), andP<0.05 was considered significant.

3. Results
The effects of temperature on the incidence ofheat-related illness in Tokyo proved that there was adefinite threshold temperature depending on age. The
incidence of heat-related illness increased in the daytime when the maximum daily temperature and theheat index temperature (a combination of daily mean
temperature and relative humidity) in summer rose
above the threshold temperature. The incidence ofheat-related illness in the elderly was higher than inyounger persons as shown in Figs. 1(a) and 1(b).

Fig. 1(a) Relationship between the incidence ofheat-related illness and the daily maximum temperature in male children (0-14
years old ○), adults (15-64 years old ●)and elderly (more than 65 years old ○)in Tokyo, Japan.
(Y-axis: incidence per million people per day
at given daily maximum temperature)

Fig. 1(b) Relationship between the incidence ofheat-related illness and the daily maximum temperature in female children(0-14 years old ○), adults (15-64 years
old ●) and elderly (more than 65 years
old ○) in Tokyo, Japan.
(Y-axis: incidence per million people per day
at given daily maximum temperature)Impact Assessment of Heat Stress on Population Health in Japan and China

The prognoses of heat-related illness patients in
Wuhan are summarized in Fig. 4(b). Fifty percent ofheat-related illness cases were inpatients in hospital.
Heat-Related Illness (1/1,000,000 person day)

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0

5

10

15

20

25

30

35

40

45

Heat Index Temperature (℃)

Fig. 2(a) Relationship between the incidence of heatrelated illness and the heat index temperaturein Tokyo, Japan.

(Y-axis: incidence per million people per day atgiven heat index temperature ; Line: exponential
regression line)

Heat-Related Illness (1/1,000,000 person day)

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0

5

10

15

20

25

30

35

40

Daily Maximum Temperature (℃)

Fig. 2(b) Relationship between the incidence of heatrelated illness and the daily maximum temperature in Tokyo, Japan.

(Y-axis: incidence per million people per day atgiven daily maximum temperature; Line: exponential regression line)

44.0
Heat-Related Illness (1/1,000,000 person day)To examine the regression models for heat-related
illness as functions of climatic variables, we analyzed
the relationship among heat-related illness, the daily
maximum temperature and the heat index temperaturein Tokyo, Japan. It was proven that the incidence ofheat-related illness increased according to rising heatindex temperature and daily maximum temperature.
The incidence of heat-related illness seemed toincrease exponentially with heat index temperature(Fig. 2(a)) and daily maximum temperature (Fig. 2(b)).
The incidence of heat-related illness was significantly
correlated with the exponential value of daily
maximum temperature (r2=0.986 P<0.001) and heatindex temperature in summer (r2=0.963 P<0.001).
The summer heat in Wuhan also seemed to affectthe incidence of heat-related illness exponentially(r2=0.922 P<0.001). However, the threshold temperature causing heat-related illness was about 5°C higher
than in Tokyo, as shown in Figs. 2(b) and 3.
The critical threshold temperature of heat-related
illness differed significantly between Tokyo andWuhan. However, the exponential relationships
between the daily maximum temperature and the incidence of heat-related illness in these cities weresimilar.
The maximum temperature in August was the mostimportant risk factor for heat-related illness in Wuhan,
China. During 1996 to 2002, the percent incident
cases of heat-related illness in June, July, August and
September were 2.2%, 84.8%, 12.6% and 0.4%,
respectively. The relationship between the monthly
maximum daily temperature and the monthly numberof cases of heat-related illness in summer had asignificant positive correlation (r2=0.828, P<0.05).
Just as in Tokyo, it was proven that men were moresensitive to heat-related illness than women in Wuhan.
The percent incidence of heat-related illness was
61.3% in men and 38.7% in women. Just as in Tokyo,
elderly persons (more than 60 years old) had a higher
risk for heat-related illness than younger ones (lessthan 60 years old). The percent incidence of heatrelated illness in elderly persons and younger oneswas 77.8% and 22.2%, respectively.
The percentage of location of outbreaks ofheat-related illness at home, outdoors and at workplaces were 37%, 36% and 27%, respectively. Morethan 70% of heat-related illness patients in Wuhan
showed hyperthermia (71.3%) and 16.1% of thepatients showed an increase in armpit body temperature to over 40°C. Fifty-eight percent of the patientswere diagnosed with heat stroke and 42%, with heatexhaustion or heat cramps.
The occupations of heat-related illness patients in
Wuhan are summarized in Fig. 4(a). Forty-three percent of heat-related illness patients were workers.
Twenty-seven percent of the patients had no occupation outside the home. The percentages of the patients
who were farmers, clerks, students and engineers were4%, 4%, 4% and 2%, respectively.

41

3.5
3.5
3
3.0
2.5
2.5
2
2.0
1.5
1.5
1
1.0
0.5
0.5
0
0.0
0

5

10
15
20
25
30
Daily Maximum Temperature (℃)

3540Fig. 3 Relationship between the incidence of heatrelated illness and the daily maximum temperature in Wuhan, China.

(Y-axis: incidence per million people per day at given
daily maximum temperature; Line: exponential regression line)

S. ASANUMA et al.

16.1
1.7
3.9

workerresident
farmerclerk
student
engineerothers

3.9
3.9

27.0

43.5(%)

GSH peroxidase, especially selenium GSH peroxidase,were strongly induced in response to increased
environmental temperatures. In aged animals, however,100
90

Incidence of Pneumonia(1/1,000,000 person day)Twenty-nine percent of the patients showed serious
syndromes and the mortality among cases ofheat-related illness was 4.2%.
When establishing preventive procedures for heatstress caused by hot summers, the temperaturedependent incidence of diseases must be analyzed.
The incidence of pneumonia differs completely depending on temperature and age as shown in Figs. 5(a),5(b) and 5(c). The highest risk group is the elderly andone of the most important factors in outbreaks ofpneumonia is the environmental temperature.
Environmental temperatures in cold and hot
climates bring a serious risk for pneumonia among theelderly. For prevention of pneumonia in the elderly, it
is necessary to improve the living environment in cold
temperatures in winter as well as in hot temperaturesin summer.
To assess the biomedical impacts of heat stress,
model experiments were carried out. Hyperthermia
was observed in animals and rectal temperature
immediately increased and exhibited thermal homeostasis after exposure to hot environments during heatstress. Oxygen free radical damage to various organs
and tissues was one of the most serious outcomes ofheat stress. In young animals, activities of protective
enzymes against oxygen free radicals, such as hepatic

80
70
60
50
40
30
20
10
0
5

10

15

20

25

30

Temperature (°C)

Fig. 5(a) Relationship between the incidence of pneumonia and the daily mean temperature in male(▬) and female (▬) children (0-14 years old)in Tokyo, Japan.

(Y-axis: incidence per million people per day atgiven daily mean temperature)

100

Incidence of Pneumonia(1/1,000,000 person day)

42

80

60

40

20

0

5

10

15

20

25

30

Temperature (°C)

Fig. 5(b) Relationship between the incidence of pneumonia and the daily mean temperature in male(▬) and female (▬) adults (15-64 years old)in Tokyo, Japan.

(Y-axis: incidence per million people per day atgiven daily mean temperature)

Fig. 4(a) Occupations of heat-related illness patients in
Wuhan, China.

2000

1.7 4.2home
1day
2-5 days
6-10 days>10 days
dead

17.1

21.6

49.6(%)

Fig. 4(b) Prognosis for inpatients undergoing treatment
for heat-related illness in hospitals in Wuhan,
China.

Incidence of Pneumonia(1/1,000,000 person day)

1800

5.8

1600
1400
1200
1000
800
600
400
200
0

5

10

15

20

25

30

Temperature (°C)

Fig. 5(c) Relationship between the incidence of pneumonia and the daily mean temperature in male(▬) and female (▬) elderly persons (morethan 65 years old) in Tokyo, Japan.

(Y-axis: incidence per million people per day atgiven daily mean temperature)Impact Assessment of Heat Stress on Population Health in Japan and China

Fig. 6(a) Age dependent hepatic catalase activity ofrats: control (■) and undergoing heat stress(■).
(In 52-week-old, 68-week-old and 100-week-old
animals, catalase activities were significantly decreased by heat stress, P<0.01)

Fig. 6(b) Age dependent hepatic lipid peroxidation of
rats: control (■) and undergoing heat stress(■).
(In 7-week-old, 52-week-old, 68-week-old and100-week-old animals, TBARS, an indicator of
lipid peroxidation, was significantly increased byheat stress, P<0.01)

GSH peroxidase and catalase were significantly decreased by heat stress as shown in Fig. 6(a). Since
activities of protective enzymes such as peroxidaseand catalase were markedly inhibited by heat stress,
an indicator of lipid peroxidation (TBARS: thibarbituric acid reacting substances) was strongly induced inaged animals as shown in Fig. 6(b).

4. Discussion
In Tokyo (Japan) and Wuhan (China), it wasproven that the incidence of heat-related illness increased exponentially with daily maximum temperature and heat index temperature. From the point ofview of adaptation, a significant difference wasobserved in the critical threshold temperature forheat-related illness in Tokyo and Wuhan. However,
the relationship between hot summer temperatures andthe incidence of heat-related illness in Japan and
China, situated in the temperate latitudes of Monsoon
Asia were completely similar. Therefore, preventionof heat-related illness will require an effective risk
management strategy for health impacts from heatstress in summer.
The incidence of heat-related illness differs com-43

pletely depending on age, and the highest risk isobserved among the elderly in Tokyo, Japan, andWuhan, China. To prevent heat-related illness in theelderly, it is necessary to adopt mitigation options for
hot temperatures. Summer heat caused by global
warming and the heat island phenomenon will bring aremarkable increase in heat stress, therefore procedures to reduce heat in urban and rural areas may benecessary in the future. Statistical forecast models forheat stress have also been established based on therelationship between heat-related illness and meteorological factors, such as heat wave temperature weather
forecast indexes established in China (Yang et al.,2000).
Since the most important site of outbreaks ofheat-related illness in Japan is outdoors, it will benecessary to improve the outside environment and tolimit outdoor activities in hot weather to reduce risks
among the elderly. In China, on the other hand, similar
numbers of outbreaks occur outdoors and at home,
therefore mitigation options are necessary for improving both indoor and outdoor conditions.
In China, occupational heat-related illness also hasa high incidence; therefore preventive measures havebeen adopted including air conditioning, reduction oflabor intensity, implementation of health standards,
education and emergency treatment (Liang, 1999; Yi
et al., 2001).
It is necessary to evaluate preventive medicine forheat stress on heat-related illness, chronic diseases andindirect human health impacts such as pneumonia,
therefore research on population impacts of heat stresswill be among the most important subjects in bioclimatology in the future. For human health, it isthought that global warming and the heat island
phenomenon may have a critical impact due to increased heat stress in summer (McGeehin & Mirabelli,2001).
Since aging and hyperthermia have a synergistic
effect on thermal damage in animals, the age-related
response of animals and humans to damage fromhyperthermia may be essential for survival and recovery from thermal injury in aging (Ando et al., 1994,
1997). These results coincide with an epidemiologicalanalysis of heat wave impacts in Nanjing, China, in1988. In heat waves, when intense heat exceeded adaily maximum temperature of 36°C, a remarkableincrease in the incidence of heat-related illness andmortality caused by heat strokes was observed inproportion to the atmospheric temperature above thethreshold value (Ando et al., 1998a, 1998b).
Since the epidemiological results and experimental
model evidence show the impacts of heat stressgreatly increase with aging, it is important to evaluate
methods of assessing the impact of increased heatstress on human populations in the future (Ando,
1998; Vandentorren et al., 2004; Conti et al., 2005).
For reducing risks of health impacts on populations
from heat stress due to global warming and the heat

44

S. ASANUMA et al.

island phenomenon, it will be necessary to improvethe environmental design of urban and rural communities and to promote the health status of residents.

5. Conclusion
The relationships between summer temperatures
and the incidence of heat-related illness in Tokyo andWuhan were strikingly similar. Furthermore, the incidence of heat-related illness increased exponentiallywith daily maximum temperature and heat index temperature.
Hot summers caused by global warming and theheat island phenomenon will bring a remarkable
health risk from pneumonia to the elderly. Therefore,
mitigation options will be necessary to improve theoutside environment.
Since aging and hyperthermia have a synergistic
effect on thermal damage in animals and humans,
understanding the age-related response of humans todamage from hyperthermia will be essential for
promoting population health.
As an option for mitigating global warming andthe heat island phenomenon, it will be necessary to
improve the environment design of urban and ruralcommunities situated in the temperate latitudes ofJapan, China and the world.

Acknowledgements
The authors express sincere gratitude to the Emergency Office of the Tokyo Metropolitan Fire Department, Japan, and the Hospital of Occupational andLabor Health in Wuhan, China. The authors are
sincerely grateful to Prof. Katsunori Sato, Faculty ofAgriculture, Okayama University, Japan, for hiscooperative work and invaluable comments on the
research.
References
Ando, M. (1998) Risk assessment of global warming on humanhealth. Global Environmental Research, 2: 69-78.
Ando, M., K. Katagiri, S. Yamamoto, S. Asanuma, M. Usuda, I.
Kawahara and K. Wakamatsu (1994) Effect of hyperthermia
on glutathione peroxidase and lipid peroxidative damage inliver. Journal of Thermal Biology, 19:177-185.
Ando, M., K. Tamura, S. Yamamoto, C.K. Liang, Y.P. Wu, J.P.
Zhang, Z.C. Mao, M.M. Yang and A.L. Chen (1996) Outlineof health effects of global climate change. Journal of
Epidemiology, 6(S): 141-144.
Ando, M., K. Katagiri, S. Yamamoto, K. Wakamatsu, I.
Kawahara, S. Asanuma, M. Usuda and K. Sasaki (1997)
Age-related effects of heat stress on protective enzymes forperoxides and microsomal monooxygenase in rat liver.
Environmental Health Perspectives, 105: 726-733.
Ando, M., K. Tamura, S. Yamamoto, C.K. Laing, Y.P. Wu, J.P.
Zhang and M.M. Yang (1998a) Direct health impacts ofclimate change in Japan and China. In: P. Curson, C. Guest

and E. Jackson, eds., Climate Change and Human Health in
Asia-Pacific Region, Australian Medical Association, 75-77.
Ando, M., N. Kobayashi, I. Kawahara, S. Asanuma and C.K.
Laing (1998b) Impacts of heat stress on hyperthermic disorders and heat stroke. Global Environmental Research, 2:
111-120.
Conti, S., P. Meli, G. Minelli, R. Solimini, V. Toccaceli, M.
Vichi, C. Beltrano and L. Perini (2005) Epidemiologic studyof mortality during the summer 2003 heat wave in Italy.
Environmental Research, 98: 390-399.
Donoghue, E.R., M.B. Kalelkar, M.A. Boehmer, J. Wilhelm, S.
Whitman, G. Good, S. Lyne, J. Lumpkin, L. Landrum and
B.J. Francis (1995) Heat-related mortality – Chicago, July
1995. MMWR, 44:577-579.
Hales, J.R.S and D.A.B. Richards (1987). Heat Stress: PhysicalExertion and Environment. Elsevier Science Ltd., Amsterdam,
The Netherlands.
Hales, J.R.S., R.W. Hubbard and S.L. Gaffin (1996) Limitationof heat tolerance. In: M.J. Fregly, C.M. Blatteis, eds., Handbook of Physiology Section 4: Environmental Physiology,
Oxford University Press, New York, 279-355.
Hawkins-Bell, L. and J.T. Rankin (1994) Heat-related deaths –Philadelphia and United States, 1993-1994. MMWR, 43:453-455.
IPCC: Emissions Scenarios (2000) Special Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, U. K. and New York, USA.
IPCC: Climate Change (2001a) The Scientific Basis-Contribution of Working Group I to the IPCC Third Assessment
Report. Cambridge University Press, Cambridge, U. K. and
New York, USA.
IPCC: Climate Change (2001b) Impacts, Adaptation, andVulnerability-Contribution of Working Group II to the IPCC
Third Assessment Report. Cambridge University Press,
Cambridge, U. K. and New York, USA.
Kalkstein, L.S. (1994) Direct impacts in cities. In: P.R. Epsteinand D. Sharp, eds., Health and Climate Change, The Lancet
Ltd., London, 26-28.
Liang, C.K. (1999) Review of global warm effect on humanhealth. Bulletin of Medical Research, 28:1-4.
McGeehin, M.A. and M. Mirabelli (2001) The potential impacts of climate variability and change on temperaturerelated morbidity and mortality in the United States. Environmental Health Perspectives, 109: 185-189.
McMichael, A.J., A. Haines, R. Sloof, S. Kovats, M. Ando, R.
Carcavallo, P.R. Epstein, G. Jendritzky, L.S. Kalkstein, J.
Patz, R.A. Odongo and W.T. Piver (1996) Climate Change
And Human Health, WHO/WMO/UNEP.
Piver, W.T., M. Ando, F. Ye and C.J. Portier (1999) Temperature and air pollution as risk factors for heat stroke in Tokyo,
July and August 1980-1995. Environmental Health Perspectives, 107: 911-916.
Snedecor, G.W. and W.G. Cochran (1967) Statistical Methods,
6th Ed. Iowa State Univ. Press, Ames.
Vandentorren, S., F. Suzan, S. Medina, M. Pascal, A. Maulpoix,
J.C. Cohen and M. Ledrans (2004) Mortality in 13 French
cities during the August 2003 heat wave. American Journalof Public Health, 94: 1518-1520.
Yang, H.Q., Z.H. Chen and J.N. Lui (2000) Epidemiologicalanalysis on heat invasion and establishment of its forecast
models in Wuhan, Journal of Hubei College of TCM,
2:51-62.
Yi, C., X.Q. Chang and Z.L. Cao (2001) Potential impact of
future climate changes on human health. Journal Environmental Health, 18:312-315.

(Received 16 January 2007, Accepted 19 February 2007)