Within the range of 25-31°C, an increase of 1 °C notably decreased older adults’ cognitive ability, including memory, attention, ability to react and calculate. The temperature rise has greater impact on women, individuals aged over 95, those who are living in rural areas, people with lower education level, or with lower level of income. 

Over the past years, everyone has experienced abnormally high temperatures or heatwaves during summer at least once. People are becoming more vulnerable to heatwaves. It can cause heat stress and heat stroke, worsen a number of health conditions, including heart disease, diabetes, mental health, and asthma. This can lead to increased death rates, especially among individuals at age of over 65. According to the Lancet Countdown on Health and Climate Change, heatwave-related death rates increased by about 85% in 2017-2021, compared with that in 2000-2004 among people in this age group.    

To explore the effects of temperature rise on cognitive ability and provide guidance for protecting older adults during heatwaves, the researchers used individuals’ data from the Chinese Longitudinal Healthy Longevity Survey. They analysed those data together with monthly average temperature data collected from a national data center. 

They included data of over 17,000 participants from the survey conducted between 2008 and 2018. By using the Mini Mental Status Examination (MMSE), the researchers assessed individuals’ cognitive ability on five aspects. They included the general ability of cognitive function, memory, attention and calculation ability, reaction ability, as well as language comprehensive and self-coordination ability. The higher the MMSE-score is, the better the cognitive ability. 

Individuals’ MMSE-scores decreased when temperature increased. Especially, within 25-31°C, every 1°C increase of monthly average temperature associated with noticeable decline in all five aspects of cognitive ability.  

Temperature rise also affected individuals’ cognitive ability unequally, in terms of their demographic and socioeconomic status. High temperatures tended to have stronger impact on women than men. Older adults at age of over 95 were more vulnerable to high temperatures. Living in rural areas, having a lower education level or income level also associated with cognitive ability decline when heatwaves happened. These findings confirm that ambient high temperature links to cognitive ability decline in Chinese older adults. 

A personal view paper, published more recently in the journal The Lancet Neurology, also showed the negative effects of heatwaves on certain brain conditions. According to an article from the University College London News reporting on this paper, the research team stated that people with dementia are susceptible to harm from extremes of temperature (e.g., heat-related illness or hypothermia) and weather events (e.g., flooding or wildfires), as cognitive impairment can limit their ability to adapt behaviour to environmental changes. 

“Reduced awareness of risk is combined with a diminished capacity to seek help or to mitigate potential harm, such as by drinking more in hot weather or by adjusting clothing,” the researchers wrote. 

This study was published in Scientific Reports. Image credit: Canva

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