Heatstroke has been known since biblical times. It is the most severe of the illnesses caused by high ambient temperature. Heat exhaustion and heat prostration are aggravated by depletion of bodily water or salt. During periods of sustained hot weather (heat waves), high rates of severe illness and death due to heatstroke may occur.
Statistics on mortality and hospital admissions show that death rates increase during extremely hot days, particularly among very old and very young people living in cities.
Extreme hot temperatures increase the number of people who die on a given day for many reasons: People with heart problems are vulnerable because their cardiovascular system must work harder to keep the body cool during hot weather. Heat exhaustion and some respiratory problems also increase.
An estimated 1,265 heat-related deaths occurred in the United States during the summer of 1980, many of them from heatstroke. In July 1995, a heat wave killed more than 700 people in the Chicago area. Studies based on these types of statistics estimate that in Atlanta, for example, even a warming of about two degrees (F) would increase heat-related deaths from the present 78 per anum to anywhere from 96 to 247 people per year.