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Our group aims to elucidate the health effects of various environmental factors at the population level with multi-disciplinary approaches. At the Department of Hygiene, we apply epidemiological approaches that combine clinical data of diseases and physiochemical/social environmental data from various sources. In addition, we will quantitatively evaluate and predict the health impact of the environment in the past, present, and future using the environment-human health risk function obtained from epidemiological studies. We also focus on global environmental issues, such as climate change, transboundary air pollution, smoke from vegetation fires, and the local environment, which tremendously impact our health.
If you are interested in our lab, go to the page of contact.
The information for the international applicants is available here.
The scholarship information is also available here.
News & Events
News & Events
Latest updates
Latest updates
Jul. 1
Dr. Md Ishtiak Rashid has joined the department as a Postdoctoral Researcher.
Apr. 3
Press Release (Research Announcement)
Collaborative Research by Associate Professor Seposo et al.: Kawasaki disease and outdoor environmental stressors: a scoping review [Jp; En]
Apr. 1
Dr. Vera Ling Hui Phung has joined the department as an Assistant Professor.
Mr. Yang Fengan and Mr. Pitsanu KHAMNUAN have enrolled in the Doctoral Program in the Social Medicine Course.
Event announcement!
Event announcement!
On 20 August 2026, Professor Hirohisa Takano will give a special lecture about environmental pollutants and allergy with toxicological perspectives. Please register ahead and join us!
Takano_flyer_en.pdfRecent publications
Recent publications
August, 2026
Environmental Epidemiology
Environmental Epidemiology
Association between ambient temperature and all-cause hospitalization by functional status in Japan: A time-stratified case-crossover study
Association between ambient temperature and all-cause hospitalization by functional status in Japan: A time-stratified case-crossover study
Differences in population vulnerability may contribute to inequities in the health impacts of temperature exposure. This study examined temperature-related hospitalization risks among vulnerable populations in Japan, using functional status as a marker of vulnerability. Functional status was assessed using the Barthel Index, which measures an individual's independence in performing activities of daily living; a score of <60 was used to define functional dependence. Consistent with existing evidence, higher risks were observed in both groups, with cold effects peaking at moderately cold temperatures. However, the ratio of relative risks revealed greater cold-related risks among functionally dependent individuals. In contrast, heat-related risks were comparable between the groups, with disparities observed only among older individuals. Targeted heat and cold prevention strategies that account for differences in vulnerability may help reduce health inequities.
Differences in population vulnerability may contribute to inequities in the health impacts of temperature exposure. This study examined temperature-related hospitalization risks among vulnerable populations in Japan, using functional status as a marker of vulnerability. Functional status was assessed using the Barthel Index, which measures an individual's independence in performing activities of daily living; a score of <60 was used to define functional dependence. Consistent with existing evidence, higher risks were observed in both groups, with cold effects peaking at moderately cold temperatures. However, the ratio of relative risks revealed greater cold-related risks among functionally dependent individuals. In contrast, heat-related risks were comparable between the groups, with disparities observed only among older individuals. Targeted heat and cold prevention strategies that account for differences in vulnerability may help reduce health inequities.
July 28, 2026
Environment & Health
Environment & Health
Diarrhea Mortality and Flood Characteristics in Southeast Asia: A Multicountry Case-Crossover Analysis
Diarrhea Mortality and Flood Characteristics in Southeast Asia: A Multicountry Case-Crossover Analysis
Flooding can increase the risk of diarrheal disease by disrupting sanitation systems, reducing hygiene conditions, and altering environmental exposures. However, the mechanisms linking flood characteristics to diarrheal outcomes remain poorly understood. In particular, it is unclear whether localized, high-depth flooding has a greater impact on diarrheal mortality than widespread, shallow flooding. Using simulated inundation data from CaMa-Flood, a global hydrodynamic model, this study investigated the associations between different flood metrics, accounting for depth and spatial extent, and diarrhea mortality across countries in Southeast Asia.
Flooding can increase the risk of diarrheal disease by disrupting sanitation systems, reducing hygiene conditions, and altering environmental exposures. However, the mechanisms linking flood characteristics to diarrheal outcomes remain poorly understood. In particular, it is unclear whether localized, high-depth flooding has a greater impact on diarrheal mortality than widespread, shallow flooding. Using simulated inundation data from CaMa-Flood, a global hydrodynamic model, this study investigated the associations between different flood metrics, accounting for depth and spatial extent, and diarrhea mortality across countries in Southeast Asia.
July 21, 2026
Environmental Epidemiology
Environmental Epidemiology
Assessing the association between floods and dengue incidence in Vietnam
Assessing the association between floods and dengue incidence in Vietnam
Does flooding affect the risks of dengue cases? This study in Vietnam assessed the monthly dengue risks due to flood events, in Vietnam nationwide and Ho Chi Minh city (a densely populated, highly urbanized and flood-prone area). The study found increased dengue risks in both settings; however, the patterns contrasted by rainy season vs. dry season. At national level, the risk was more pronounced during the rainy season, whereas in Ho Chi Minh city, it was more prominent during the dry season. Lagged effects were observed in both seasons, suggesting a flushing-drying mechanism that interrupts the breeding and transmission cycles of dengue. The findings have important public health implications, highlighting the need for location- and season-specific dengue surveillance and timely vector control measures.
Does flooding affect the risks of dengue cases? This study in Vietnam assessed the monthly dengue risks due to flood events, in Vietnam nationwide and Ho Chi Minh city (a densely populated, highly urbanized and flood-prone area). The study found increased dengue risks in both settings; however, the patterns contrasted by rainy season vs. dry season. At national level, the risk was more pronounced during the rainy season, whereas in Ho Chi Minh city, it was more prominent during the dry season. Lagged effects were observed in both seasons, suggesting a flushing-drying mechanism that interrupts the breeding and transmission cycles of dengue. The findings have important public health implications, highlighting the need for location- and season-specific dengue surveillance and timely vector control measures.
September 1, 2026
Environmental Research
Environmental Research
Minimum mortality temperature by cause of death and age group: A multi-country observational study (1990-2019)
Minimum mortality temperature by cause of death and age group: A multi-country observational study (1990-2019)
The relationship between temperature and mortality is typically characterized by a U- or J-shaped curve. The temperature at which the mortality risk is at the lowest is known as minimum mortality temperature (MMT), and its percentile (MMTP). These temperatures reflect population adaptation to local temperature conditions. Using a Multi-Country Multi-City Collaborative Research Network dataset, this study found varying MMT and MMTP across age and specific causes of death, suggesting that physiological responses to temperature differ among population subgroups.
The relationship between temperature and mortality is typically characterized by a U- or J-shaped curve. The temperature at which the mortality risk is at the lowest is known as minimum mortality temperature (MMT), and its percentile (MMTP). These temperatures reflect population adaptation to local temperature conditions. Using a Multi-Country Multi-City Collaborative Research Network dataset, this study found varying MMT and MMTP across age and specific causes of death, suggesting that physiological responses to temperature differ among population subgroups.
May 1, 2026
eClinicalMedicine
eClinicalMedicine
Mortality risk due to non-optimum temperatures by cause of death, age, and sex: a multi-country time-series study
Mortality risk due to non-optimum temperatures by cause of death, age, and sex: a multi-country time-series study
Understanding the distinct temperature–mortality relationships across various causes of death can help guide targeted interventions. This multi-country study characterised cause-, age-, and sex-specific mortality risks asosciated with non-optimum temperatures. Cold temperatures accounted for the largest mortality burden, emphasising the need for increased caution during cold periods. Conversely, for infectious diseases and injury/external causes, greater attention is required during heat events. The observed variation in age- and sex-specific mortality risks across different causes highlights the importance of tailored public health strategies addressing the unique vulnerabilities of specific demographic groups. Future work should improve estimation in data-sparse subgroups and develop cause-, age-, and sex-specific projections of temperature-related health risks under future climate scenarios.
Understanding the distinct temperature–mortality relationships across various causes of death can help guide targeted interventions. This multi-country study characterised cause-, age-, and sex-specific mortality risks asosciated with non-optimum temperatures. Cold temperatures accounted for the largest mortality burden, emphasising the need for increased caution during cold periods. Conversely, for infectious diseases and injury/external causes, greater attention is required during heat events. The observed variation in age- and sex-specific mortality risks across different causes highlights the importance of tailored public health strategies addressing the unique vulnerabilities of specific demographic groups. Future work should improve estimation in data-sparse subgroups and develop cause-, age-, and sex-specific projections of temperature-related health risks under future climate scenarios.
Apr 19, 2026
Sustainable Science
Sustainable Science
Assessing the clean air and health co-benefits of net zero transitions in Hachinohe and Niigata, Japan
Assessing the clean air and health co-benefits of net zero transitions in Hachinohe and Niigata, Japan
Factoring clean air and health co-benefits into urban climate plans can reduce cost concerns and build multi-stakeholder support for net-zero transitions. Most of the research estimating these co-benefits has focused on large cities. Limited research has concentrated on small- and medium-sized cities. Small- and medium-sized cities merit more attention since they tend to have different energy and industrial structures and less technical capacity to estimate co-benefits than larger cities. This paper therefore demonstrates how differences in these structures and other contextual factors influence the co-benefits from net-zero transport, energy, industry and waste policies in two small- to medium-sized cities in Japan: Hachinohe city and Niigata city.
Factoring clean air and health co-benefits into urban climate plans can reduce cost concerns and build multi-stakeholder support for net-zero transitions. Most of the research estimating these co-benefits has focused on large cities. Limited research has concentrated on small- and medium-sized cities. Small- and medium-sized cities merit more attention since they tend to have different energy and industrial structures and less technical capacity to estimate co-benefits than larger cities. This paper therefore demonstrates how differences in these structures and other contextual factors influence the co-benefits from net-zero transport, energy, industry and waste policies in two small- to medium-sized cities in Japan: Hachinohe city and Niigata city.
Feb 21, 2026
Environmental Research Communications
Environmental Research Communications
High ground level ozone amplifies heat-related illnesses in Japan: a nationally representative analysis
High ground level ozone amplifies heat-related illnesses in Japan: a nationally representative analysis
Dr. Mustakim from our laboratory found, using nationwide data, that high ozone concentrations amplify the risk of heat-related illness.
Dr. Mustakim from our laboratory found, using nationwide data, that high ozone concentrations amplify the risk of heat-related illness.
February 11, 2026
Circulation Reports
Circulation Reports
Impact of Snowfall on Ambulance Response Times to Out-of-Hospital Cardiac Arrest ― Nationally-Representative Population-Based Registry Analysis, 2009–2019 ―
Impact of Snowfall on Ambulance Response Times to Out-of-Hospital Cardiac Arrest ― Nationally-Representative Population-Based Registry Analysis, 2009–2019 ―
This nationwide Japanese study found that heavy snowfall significantly delayed emergency medical service response times to out-of-hospital cardiac arrest. Snow-related delays occurred across regions and may adversely affect survival and neurological outcomes, highlighting the need for resilient emergency systems during extreme winter conditions.
This nationwide Japanese study found that heavy snowfall significantly delayed emergency medical service response times to out-of-hospital cardiac arrest. Snow-related delays occurred across regions and may adversely affect survival and neurological outcomes, highlighting the need for resilient emergency systems during extreme winter conditions.
January 21, 2026
Geriatric Nursing
Geriatric Nursing
New Insights into Behavioral and Psychological Symptoms of Dementia
New Insights into Behavioral and Psychological Symptoms of Dementia
This study applied item response theory to behavioral and psychological symptoms of dementia in long-term care residents. Certain symptoms appeared early, while greater cognitive impairment was associated with higher latent symptom severity, suggesting potential for predicting symptom onset and improving care planning.
This study applied item response theory to behavioral and psychological symptoms of dementia in long-term care residents. Certain symptoms appeared early, while greater cognitive impairment was associated with higher latent symptom severity, suggesting potential for predicting symptom onset and improving care planning.
December 1, 2025
News release in EnrekAlert!
November 9, 2025
Scientific Reports
Scientific Reports
Why Do Residents Underestimate Air Pollution from Stubble Burning in Punjab, India?
Why Do Residents Underestimate Air Pollution from Stubble Burning in Punjab, India?
This study surveyed 2,202 households across Punjab to understand perceptions of air pollution and stubble burning. While many residents recognized severe air pollution in Delhi, fewer acknowledged the impact of local stubble burning on health. Households with existing health issues were more likely to perceive the smoke as harmful.
This study surveyed 2,202 households across Punjab to understand perceptions of air pollution and stubble burning. While many residents recognized severe air pollution in Delhi, fewer acknowledged the impact of local stubble burning on health. Households with existing health issues were more likely to perceive the smoke as harmful.
October 20, 2025
International Journal of Epidemiology
International Journal of Epidemiology
Effects of smoke haze on respiratory clinic visits in Central Kalimantan, Indonesia according to different haze characteristics
Effects of smoke haze on respiratory clinic visits in Central Kalimantan, Indonesia according to different haze characteristics
Vegetation and peat fires are expected to increase under climate extremes. Smoke haze is a common air-pollution issue in Southeast Asia. We sought to understand how haze affects visits to primary healthcare centers for respiratory illness. The effects of haze were inconclusive, although they appeared to be stronger in the area with more frequent fire-haze days.
Vegetation and peat fires are expected to increase under climate extremes. Smoke haze is a common air-pollution issue in Southeast Asia. We sought to understand how haze affects visits to primary healthcare centers for respiratory illness. The effects of haze were inconclusive, although they appeared to be stronger in the area with more frequent fire-haze days.
August 28, 2025
Hokkaido University and University Hospital Cologne will co-host a symposium on "Bridging Nations, Protecting Generations: Prevention Strategies against Climate-sensitive Diseases in Elderly Populations of Japan and Germany"
Hokkaido University and University Hospital Cologne will co-host a symposium on "Bridging Nations, Protecting Generations: Prevention Strategies against Climate-sensitive Diseases in Elderly Populations of Japan and Germany"
◆ Date: August 28 (Thursday), 2025
◆ Date: August 28 (Thursday), 2025
◆ Language: English
◆ Language: English
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