Elderly people who use electric fans during extreme heat may have higher heart rates and core temperatures compared to having no fan, according to a small study.
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 co-author Craig G. Crandall of the University of Texas Southwestern Medical Centre 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 said. “This is specific to very extreme conditions.”
At lower temperatures, fans are beneficial, he said.
Crandall and his co-authors 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˚C for a total of 100 minutes. The relative humidity of the room increased from 30 per cent to 70 per cent 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 40cm electric fan facing them from one metre 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.
I would not want someone based on these results to change their behaviour
For heart rate, rapid increase began at about 53 per cent relative humidity with a fan and 56 per cent without a fan. For core temperature, the average inflection point occurred at 65 per cent with a fan and 63 per cent without a fan, Crandall’s team reports in a research letter in Jama. Sweat loss was the same with and without fans, at 0.8 litres.
“It’s important that people don’t stop using fans in less extreme conditions,” Crandall said.
Temperatures in this study modelled the 1995 Chicago heatwave. “These specific conditions are admittedly rare.
Limitations of the study include the fact that it tested extreme heat conditions. Researchers found that fans worked best for younger people at 36˚C, a more common heatwave 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 behaviour,” 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 neighbour’s, with friends or family, or a movie theatre until the heat breaks,” he said.