Heat kills thousands not hundreds in the U.S.

As temperatures rise this summer, a new study finds that thousands of U.S. deaths may be attributable to heat each year – far more than the 600 deaths previously estimated by the Centers for Disease Control and Prevention (CDC).

The study by researchers from Boston University School of Public Health and the University of British Columbia School of Population and Public Health estimates that heat contributed to the deaths of 5,600 people each year on average between 1997 and 2006 in 297 counties, comprising three-fifths of the U.S. population.

Most of these deaths were from only moderately hot weather, rather than extremely hot weather – categories that the researcher defined not by temperature, but by what temperatures are normal for a given region of the U.S., explains a statement.

“How dangerous a hot day is may depend on where you live,” says study lead author Kate R. Weinberger in the statement. “A 90˚F day might be dangerous in Seattle, but not in Phoenix. One of the factors that gives rise to this phenomenon is differing degrees of adaptation to heat. For example, air conditioning is much more common in cities like Phoenix that experience hot weather frequently versus cities like Seattle with cooler climates.”

Weinberger says, noting that demographic factors can also affect how vulnerable a population is to heat, heat especially endangers older adults, children, pregnant women, and outdoor workers.

The researchers used data from the National Center for Health Statistics on deaths in the most populous counties (1997 to 2006 was the most recent decade with continuous data available), and the Parameter-elevation Relationships on Independent Slopes Model (PRISM), which estimates temperatures across the contiguous US down to the four-square-kilometer area.

While most previous research has focused on the information provided on death records to try to estimate deaths from heat, this study analyzed the association between days considered moderately or extremely hot in that county and the number of deaths from any cause, showing that not hundreds but thousands of deaths are tied to heat.

The researchers estimated that moderate heat killed 3,309 people per year in the counties included in the study, and extreme heat killed 2,299 people each year.

Photo credit: Flickr Creative Commons

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