New collaborative research from the University of Sydney and the Montreal Heart Institute has shown that using a fan in hot and humid weather reduces cardiac strain in older people, contradicting recommendations from the Centers of Disease Control and Prevention in the US.

The study, published in the New England Journal of Medicine, looked at the efficacy of different low-cost cooling strategies—such as electric fans with and without spraying water on the skin—for older adults, who are known to be at a heightened health risk during hot summer weather.

Professor Ollie Jay, Director of the Heat and Health Research Center and Thermal Ergonomics Laboratory in the Faculty of Medicine and Health said, "Health hazards from extreme heat are becoming increasingly common because of climate change.

"Older adults, especially those with heart disease, are at greater risk due to the strain that hot temperatures put on the heart. Understanding the impacts of different cooling strategies on the heart is important to help vulnerable people stay well during hot summer weather."

The study exposed older participants with and without heart disease to two environments—one hot and humid (38°C and 60% humidity) and the other very hot and dry (45°C and 15% humidity); conditions chosen to represent the two most common heat wave extremes globally.

The team found that in hot and humid conditions, fan use with and without skin wetting reduced heat-induced cardiac strain in older people.

However, in very hot and dry conditions, fan use had an adverse effect by tripling the increase in cardiac strain, which could be fatal for someone with heart disease. This is because, although fans help sweat evaporate, in very hot and dry conditions the effect is small and counteracted by convection forcing more heat into the body. Instead, in these conditions, skin wetting used on its own was effective at reducing the work of the heart.

Co-author of the study, Dr. Daniel Gagnon from the Montreal Heart Institute said, "While air conditioning is an effective way of staying cool, it's not available to everyone, especially those most vulnerable to the heat such as the elderly and people with heart disease—so it's positive news that low-cost alternatives are effective.

"Importantly, the study has shown that the weather conditions affect the type of cooling strategy that should be used—a vital piece of information that will help older people to stay safe in heat waves."

Dr. Georgia Chaseling, who led data collection in Montreal during her time as a post-doctoral researcher, and now co-leads the "Aging and Chronic Diseases" priority research theme in the Heat and Health Research Center at the University of Sydney adds, "The interventions that we tested seem simple, but they are necessarily so because we wanted to figure out which solutions people living in low-resource settings without access to air-conditioning should and should not be using."