TY - JOUR
T1 - The Role of Humidity in Associations of High Temperature with Mortality
T2 - A Multiauthor, Multicity Study
AU - Armstrong, Ben
AU - Sera, Francesco
AU - Vicedo-Cabrera, Ana Maria
AU - Abrutzky, Rosana
AU - Åström, Daniel Oudin
AU - Bell, Michelle L.
AU - Chen, Bing Yu
AU - de Sousa Zanotti Stagliorio Coelho, Micheline
AU - Correa, Patricia Matus
AU - Dang, Tran Ngoc
AU - Diaz, Magali Hurtado
AU - Dung, Do Van
AU - Forsberg, Bertil
AU - Goodman, Patrick
AU - Guo, Yue Liang Leon
AU - Guo, Yuming
AU - Hashizume, Masahiro
AU - Honda, Yasushi
AU - Indermitte, Ene
AU - Íñiguez, Carmen
AU - Kan, Haidong
AU - Kim, Ho
AU - Kyselý, Jan
AU - Lavigne, Eric
AU - Michelozzi, Paola
AU - Orru, Hans
AU - Ortega, Nicolás Valdés
AU - Pascal, Mathilde
AU - Ragettli, Martina S.
AU - Saldiva, Paulo Hilario Nascimento
AU - Schwartz, Joel
AU - Scortichini, Matteo
AU - Seposo, Xerxes
AU - Tobias, Aurelio
AU - Tong, Shilu
AU - Urban, Aleš
AU - De la Cruz Valencia, César
AU - Zanobetti, Antonella
AU - Zeka, Ariana
AU - Gasparrini, Antonio
PY - 2019/9
Y1 - 2019/9
N2 - BACKGROUND: There is strong experimental evidence that physiologic stress from high temperatures is greater if humidity is higher. However, heat indices developed to allow for this have not consistently predicted mortality better than dry-bulb temperature. OBJECTIVES: We aimed to clarify the potential contribution of humidity an addition to temperature in predicting daily mortality in summer by using a large multicountry dataset. METHODS: In 445 cities in 24 countries, we fit a time-series regression model for summer mortality with a distributed lag nonlinear model (DLNM) for temperature (up to lag 3) and supplemented this with a range of terms for relative humidity (RH) and its interaction with temperature. City-specific associations were summarized using meta-analytic techniques. RESULTS: Adding a linear term for RH to the temperature term improved fit slightly, with an increase of 23% in RH (the 99th percentile anomaly) associated with a 1.1% [95% confidence interval (CI): 0.8, 1.3] decrease in mortality. Allowing curvature in the RH term or adding terms for interaction of RH with temperature did not improve the model fit. The humidity-related decreased risk was made up of a positive coefficient at lag 0 outweighed by negative coefficients at lags of 1-3 d. Key results were broadly robust to small model changes and replacing RH with absolute measures of humidity. Replacing temperature with apparent temperature, a metric combining humidity and temperature, reduced goodness of fit slightly. DISCUSSION: The absence of a positive association of humidity with mortality in summer in this large multinational study is counter to expectations from physiologic studies, though consistent with previous epidemiologic studies finding little evidence for improved prediction by heat indices. The result that there was a small negative average association of humidity with mortality should be interpreted cautiously; the lag structure has unclear interpretation and suggests the need for future work to clarify. https://doi.org/10.1289/EHP5430.
AB - BACKGROUND: There is strong experimental evidence that physiologic stress from high temperatures is greater if humidity is higher. However, heat indices developed to allow for this have not consistently predicted mortality better than dry-bulb temperature. OBJECTIVES: We aimed to clarify the potential contribution of humidity an addition to temperature in predicting daily mortality in summer by using a large multicountry dataset. METHODS: In 445 cities in 24 countries, we fit a time-series regression model for summer mortality with a distributed lag nonlinear model (DLNM) for temperature (up to lag 3) and supplemented this with a range of terms for relative humidity (RH) and its interaction with temperature. City-specific associations were summarized using meta-analytic techniques. RESULTS: Adding a linear term for RH to the temperature term improved fit slightly, with an increase of 23% in RH (the 99th percentile anomaly) associated with a 1.1% [95% confidence interval (CI): 0.8, 1.3] decrease in mortality. Allowing curvature in the RH term or adding terms for interaction of RH with temperature did not improve the model fit. The humidity-related decreased risk was made up of a positive coefficient at lag 0 outweighed by negative coefficients at lags of 1-3 d. Key results were broadly robust to small model changes and replacing RH with absolute measures of humidity. Replacing temperature with apparent temperature, a metric combining humidity and temperature, reduced goodness of fit slightly. DISCUSSION: The absence of a positive association of humidity with mortality in summer in this large multinational study is counter to expectations from physiologic studies, though consistent with previous epidemiologic studies finding little evidence for improved prediction by heat indices. The result that there was a small negative average association of humidity with mortality should be interpreted cautiously; the lag structure has unclear interpretation and suggests the need for future work to clarify. https://doi.org/10.1289/EHP5430.
UR - http://www.scopus.com/inward/record.url?scp=85072666411&partnerID=8YFLogxK
U2 - 10.1289/EHP5430
DO - 10.1289/EHP5430
M3 - Article
C2 - 31553655
AN - SCOPUS:85072666411
VL - 127
JO - Environmental Health Perspectives
JF - Environmental Health Perspectives
SN - 0091-6765
IS - 9
M1 - 097007
ER -
