Heat waves can harm people's health in unexpected ways, according to a new report.
While it has been thought that in cities, people living alone or in big apartment buildings are the most susceptible, a new analysis of heat-related illnesses and deaths in New York City suggests the real problem is not necessarily where a person lives, but that hyperthermia can kill a person quickly without showing obvious warning signs.
For the report, New York City health officials looked at heat waves that struck the city between 2000 and 2011, and found that unlike what previous studies suggested, people who died from hyperthermia were not more likely to live in multifamily apartment buildings, or to live alone than the general population of the city.
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"Hyperthermia can progress rapidly, and many persons might not be aware of the warning signs, including lack of sweating in late-stage illness," the researchers at the New York Department of Health and Mental Hygiene wrote in their report.
The analysis showed that an average of 447 people visited emergency rooms yearly because of heat-related illnesses and were released, another 152 people on average were admitted to hospitals, and 13 died from heat-related illnesses.
Most people affected by hyperthermia were at home, and none of them had a working air conditioner. Temperatures inside a home can reach 18 degrees Fahrenheit (10 degrees Celsius) higher than outside temperatures, which can reach 95 to 100 F (35 to 38 C) or higher during heat waves in New York.
Hyperthermia happens when a person's body absorbs more heat than it dissipates, which leads to dangerously high body temperatures that require medical attention.
One sign of hyperthermia is dry skin, which occurs as the body fails to cool down through sweating. Headaches, dizziness and nausea are other symptoms.
Every year, about 650 Americans die from hyperthermia — a death toll greater than that of tornadoes, hurricanes, floods and earthquakes combined, according to the Centers for Disease Control and Prevention.
As the U.S. population grows older and summer temperatures rise from climate change, increasingly more people may be at risk for hyperthermia, the researchers said.
Older adults, and people with other health problems or with mental conditions, as well as those who don't have access to air conditioning at home, are at the highest risk of dying from hyperthermia, the researchers said.
Another risk factor is weight; among New Yorkers who died from heat stroke, 48 percent were obese and another 29 percent were overweight.
Email Bahar Gholipour. Follow LiveScience @livescience, Facebook & Google+. Original article on Live Science.
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