Many people aged 70 and older don’t take the precautions they should during episodes of extreme summer heat, a new study suggests.

As heat waves grip most of the country this summer, many older Americans fail to take the protective measures that could save their lives when heat advisories are issued, according to researchers at Kent State University in Ohio.

Only half of people aged 65 years of age or older surveyed said they changed their behavior in response to heat warnings issued by officials. However, almost 90% claimed to be aware of the warnings, researchers said. Nearly 3,500 Americans died from heat-related causes between 1999 and 2003, according to data from the U.S. Centers for Disease Control and Prevention. The study was published in the International Journal of Biometeorology.