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 For younger people, using a fan delays elevations in heart rate and
core temperature by speeding up sweat evaporation from the skin, but
older people do not sweat as much so their bodies react differently,
said coauthor Craig G. Crandall of the University of Texas
Southwestern Medical Center in Dallas.
“One of the biggest fears that we have about this study is we’ll
have people stop using fans and that’s not what we want,” Crandall
told Reuters Health by phone. “This is specific to very extreme
conditions.”
At lower temperatures, fans are beneficial, he said.
Crandall and his coauthors studied three men and six women between
ages 60 and 80 in the Dallas and Fort Worth areas. The participants
wore shorts or shorts and a sports bra in a room maintained at 42
degrees Celsius, about 107 degrees Fahrenheit, for a total of 100
minutes. The relative humidity of the room increased from 30 percent
to 70 percent by the end of the session. They did not drink water
during the session.
Each participant completed the heat test twice on separate days,
once with a 16-inch electric fan facing them from one meter away and
once without a fan. Researchers measured their heart rates, core
temperatures and sweat loss, looking for the relative humidity level
where each participant’s heart rate and core temperature began to
increase rapidly, the “critical relative humidity.”
Other than for one participant, whose core temperature and heart
rate did not start to increase rapidly in either condition, there
were small differences in critical relative humidities for fan and
no-fan tests.
For heart rate, rapid increase began at about 53 percent relative
humidity with a fan and 56 percent without a fan. For core
temperature, the average inflection point occurred at 65 percent
with a fan and 63 percent without a fan, Crandall’s team reports in
a JAMA research letter.
Sweat loss was the same with and without fans, at 0.8 liters (1.69
pints).
“It’s important that people don’t stop using fans in less extreme
conditions,” Crandall said. Temperatures in this study modeled the
1995 Chicago heat wave, so they do happen, but very rarely in the
U.S., he said.
“These specific conditions are admittedly rare,” he said.
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The older you get, the less you sweat under heat stress, Crandall
said. But sweating helps your body adapt to heat. Some young people
may complain that they sweat “too much,” but as long as you stay
hydrated and replace the fluids lost, your body is working properly,
he said.
Limitations of the study include the fact that it tested extreme
heat conditions. Researchers found that fans worked best for younger
people at 36 degrees Celsius (96.8 F), a more common heat wave
temperature. But it remains “unclear if the same is true for elderly
adults,” the researchers write. Further studies are also needed to
see what happens to people with other health conditions, they add.
“I would not want someone based on these results to change their
behavior,” Crandall said. “I’d still want the elderly with air
conditioning that is broken down to use a fan.”
The results may be more relevant where air conditioning is less
common, he said.
“In fact what really should be done, if it’s that hot and the A/C is
broken, you should find somewhere to go where there is A/C, like a
neighbor’s, with friends or family, or a movie theater until the
heat breaks,” he said.
SOURCE: http://bit.ly/2bRaNLH JAMA, online September 6, 2016.
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