Providing elderly adults with electric fans during extreme heat and humidity increased their heart rate and core temperature, according to a study in Texas.

Lead researcher Daniel Gagnon, PhD, of the University of Texas Southwestern Medical Center in Dallas, and colleagues published their results online in JAMA on Sept. 6.

The researchers enrolled three men and six women who were between 60 and 80 years old. The adults, who were from the Dallas and Fort Worth areas, volunteered to participate in the study, running from June 2015 to January 2016.

“We know that fans keep young adults cooler by increasing the evaporation of sweat,” Craig G. Crandall, PhD, one of the study’s authors, said in a news release. “We surmise that age-related impairments in sweating capacity make fans an ineffective means of cooling for the elderly during exceptionally hot days, and may, in fact, increase thermal and cardiac strain.”

The participants sat in a chamber maintained at approximately 108 degrees for 30 minutes at a relative humidity of 30 percent. The humidity was then increased 2 percent every five minutes until it reached 70 percent.

On separate days, participants performed the protocol with a 16-inch fan facing them from one meter with an air velocity of four meters per second. They did not have the fan on them during the other days. During the protocol, men wore shorts and women wore shorts and a sports bra, but neither group was allowed to drink fluids.

The researchers measured the participants’ heart rate from an electrocardiogram, core temperature from an esophageal thermocouple and sweat loss from nude body weight measurements.

The critical relative humidity values for heart rate were 53 percent when fans were turned on and 56 percent when there were no fans, while the core temperature values were 65 percent and 63 percent, respectively.

Although those values were similar between the groups, the researchers noted that there were significant condition x relative humidity interactions for heart rate and core temperature. Participants who used fans had higher heart rates and core temperatures, but the researchers noted the magnitude of the differences typically was less as relative humidity increased.

“Although differences were small, their cumulative effect may become clinically important with fan use during more prolonged heat exposure,” the researchers wrote.

They added that sweat loss was similar among participants who used fans and those who did not use fans, which they noted might limit the fans’ effectiveness.

“Overall, this preliminary study indicates that electric fans may be detrimental for attenuating cardiovascular and thermal strain of elderly adults during heat waves,” the researchers wrote.

Previous research showed that the use of fans was most effective in young adults when the temperature was 98.6 degrees. However, the researchers mentioned that this study examined a temperature of 108 degrees, which could have been a limitation.

“Studies are also needed to examine fan use in other vulnerable populations during heat waves, such as those with disease and comorbidities,” they wrote.