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Member Research & Reports

Member Research & Reports

Washington Finds Hot Humid Days Increase Risk of Hospitalization and Death

In two just-released studies, researchers at the University of Washington show that hot weather in King County (which includes Seattle) is associated with adverse health outcomes, including hospitalization and death.

Tania Busch Isaksen
[Photo: Dr. Tania Busch Isaksen]

“As climate change increases the intensity and duration of our extreme-heat events, we can reasonably expect vulnerable populations to see an increase in hospitalizations and deaths,” said Dr. Tania Busch Isaksen, lead author of the studies and a research scientist in the Department of Environmental and Occupational Health Sciences in the University of Washington  School of Public Health.

Heat is measured by combining both the daily maximum outside temperature and relative humidity to reflect the humidex, what to an average person is a “feels-like” temperature. This means a day with a high of 84°F (28.9°C) and 60% humidity has a humidex of 97°F or 36°C.

In the last 30 years, 114 days in King County have been at or above a humidex of 97°F; typically, only one percent of the days per year are hotter than this humidex temperature.

During the same period, Dr. Busch Isaksen found a 10 percent increase in the risk of death for all ages and for all causes on days exceeding 36.1°C humidex. She found people older than 65 and those aged 45-64 years with diabetes were particularly vulnerable. The increased risk for those with diabetes, she explained, may be due to a number of underlying health-related factors such as an electrolyte imbalance or an increase in blood glucose levels as the temperature rises.

The elderly (85 years or older) were most at risk of hospitalization and death. Physiologically, aged bodies are less effective at dissipating heat. Additionally, underlying health conditions and medication use can influence thermal-regulating biomechanisms.

When Busch Isaksen and co-authors compared hospital records with meteorological data from 1990 to 2010, they found increased heat-related admissions for age groups 15 years and older, and increased admissions for acute renal failure in the 45-64 age group.  Diabetic patients are at elevated risk for kidney disease and may be particularly vulnerable to heat-related health problems.

Co-authors include Dr. Richard Fenske, Dr. Michael Yost, and graduate students Ms. Elizabeth Hom, Ms. You Ren, and Ms. Hilary Lyons, all from the University of Washington.

Links to studies:;jsessionid=3FCCBC8F6B5DF8527E3B1522B538490F