A pioneering study performed in Brazil found that older adults in good physical and mental health continued to display normal cognitive performance in terms of memory, attention and reaction time even at an ambient temperature of 32°C (photo: Wikimedia Commons)

Healthy older people tolerate heat stress, but not high humidity
2016-02-10

A pioneering study found that older adults in good physical and mental health continued to display normal cognitive performance in terms of memory, attention and reaction time even at an ambient temperature of 32°C.

Healthy older people tolerate heat stress, but not high humidity

A pioneering study found that older adults in good physical and mental health continued to display normal cognitive performance in terms of memory, attention and reaction time even at an ambient temperature of 32°C.

2016-02-10

A pioneering study performed in Brazil found that older adults in good physical and mental health continued to display normal cognitive performance in terms of memory, attention and reaction time even at an ambient temperature of 32°C (photo: Wikimedia Commons)

 

By Elton Alisson  |  Agência FAPESP – Older people are vulnerable to the effects of very warm weather, such as the record high temperatures recorded in different parts of the world in recent years. Among these effects are alterations in the mechanisms that control body temperature, according to specialists in geriatric medicine.

However, a study by researchers at the University of São Paulo’s Medical School (FM-USP) and Institute of Astronomy, Geophysics & Atmospheric Sciences (IAG-USP) in Brazil has found that healthy seniors can maintain satisfactory cognitive function at temperatures as high as 32°C, typical of a warm summer day in São Paulo.

The study was part of a project conducted under the aegis of the National Institute for Integrated Analysis of Environmental Risk, one of the National Science & Technology Institutes (INCTs) supported by FAPESP and the National Council for Scientific & Technological Development (CNPq) in São Paulo State. A paper detailing the results has been published in Age, the American Aging Association’s official journal.

“We found that the cognitive performance of older people with good functioning wasn’t adversely affected by such high temperatures,” Beatriz Maria Trezza, a geriatrician at FM-USP’s teaching hospital, Hospital das Clínicas, and lead author of the study, told Agência FAPESP.

The researchers measured the effects of heat stress on cognitive performance in 68 individuals with an average age of 73.3 years, all of whom were cognitively and physically healthy (able to walk independently and enjoying sound mental health, among other aspects). The subjects were patients of the geriatric service of Hospital das Clínicas or participants in USP’s “University Open to the Third Age” program.

The study consisted of a controlled clinical trial in which the subjects were administered a battery of five computerized neuropsychological tests successively conducted in rooms with air temperatures set at 24°C (considered comfortable for moderate exercise) and 32°C.

Selected from the Cambridge Neuropsychological Test Automated Battery (CANTAB), a computer-based cognitive assessment system originally developed at Cambridge University in England, the five tests assessed different aspects of the subjects’ cognitive performance, such as memory, attention, visual stimulus reaction and learning.

There were no significant differences between the cognitive performance assessed at 32°C and that at 24°C.

“Overall analysis of the test results showed that these subjects’ cognitive performance remained the same in the environment at 32°C,” Trezza said. “However, our sample was highly specific and possibly less vulnerable to heat stress than many old people.”

Humidity and physical activity

The researchers also performed cognitive interaction analysis by dividing the subjects into different groups – men only, women only (69% of the total sample), older subjects, and more active or sedentary – to determine whether any were more susceptible to the effects of higher temperatures.

In one such experiment, two groups were exposed to the same temperature (32°C) but different levels of relative air humidity. One group was administered the test battery in a room with 57.8% maximum humidity (the median for the heat variation tests), and the other in a room with higher humidity. The researchers found that the cognitive performance of the group exposed to 32°C and humidity above 57.8% was adversely affected by the more humid heat.

In contrast, a group of 33 participants exposed to drier heat, with 57.8% humidity or less, displayed no cognitive impairments compared with the control group.

“We were able to calibrate temperature precisely during the heat stress test, but it was harder to do so with humidity,” Trezza said.

Through a Thematic Project supported by FAPESP, the researchers are conducting another test battery with subjects of the same average age to compare cognitive performance at different levels of humidity and under heat stress (32°C).

“We want to make sure it’s humidity that most affects the cognitive performance of older people because heat stress alone made no difference,” said Fábio Luiz Teixeira Gonçalves, a professor at IAG-USP and principal investigator for the Thematic Project.

The researchers do not know exactly why humidity levels influence cognitive performance. One hypothesis is that the higher the humidity at high temperatures, the greater the stress caused to the human body by heat, according to Trezza.

This is because on very warm days, such as when the temperature is above 30°C, sweating is one of the body’s main ways of losing heat, and this is harder when the relative air humidity is already high. As a result, it is more difficult for the body to regulate its temperature in warm humid weather, especially for older people.

“Heat stress competes with cognitive performance,” Trezza explained. “The neural networks involved in trying to keep the body’s temperature stable have to deal with other issues at the same time.”

The researchers also found that the frequency of physical activity influenced the effects of heat on the older subjects’ cognitive performance.

The cognitive performance of participants who exercised less than four times a week was not as good under heat stress as that of the subjects who exercised more frequently.

“People who take regular exercise have better thermoregulatory control than sedentary people,” Trezza said. “Physical activity raises the body’s temperature and it ‘learns’ to dissipate heat.”

Groundbreaking study

According to Trezza, this was the first controlled clinical trial ever to investigate the effects of heat stress on cognitive performance in older people.

The effects of heat stress on the cognitive performance of military personnel, industrial workers exposed to extreme environments and younger people are well studied, but no such research has hitherto focused on older adults.

“We’re currently experiencing a process of population aging alongside global climate change. One of the goals of this study was to try to understand how older people whose thermoregulatory control is changing can adapt to a warmer climate,” Trezza said.

Newborn infants and older people have suffered the most from recent heat waves in different parts of the world, such as during the summer of 2003 in Europe.

“Older people are less sensitive to heat and don’t notice temperature variations as quickly as younger people, so their behavioral responses often show a significant lag,” Trezza said.

When asked whether they felt comfortable or uncomfortable at temperatures of approximately 32°C, about a third of the participants in the study said they felt comfortable.

The article “Environmental heat exposure and cognitive performance in older adults: a controlled trial” (doi: 10.1007/s11357-015-9783-z) by Trezza et al. can be read in the journal Age at link.springer.com/article/10.1007%2Fs11357-015-9783-z.

 

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