The Israel Electric Corporation – concerned that excessive use of air conditioners will cause power outages during the current heatwave – would be happy to see more people using electric fans during peak use instead. But a new systemic review by the prestigious Cochrane Library has not found reliable evidence that fans are of any benefit to health in temperatures over 35 degrees Celsius.

The just-published study was conducted by Cochrane’s UK-based, nonprofit international network of scientists from over 100 countries, who sought to determine the reliability of medical discoveries based on evidence.

The review found no high quality evidence to guide future national and international policies, and outlined the type of study that would help resolve the uncertainty – presented in a podcast and an editorial published Thursday.

Heatwaves in Europe and the US have led to increasing interest in health protection measures to reduce the impact of such extreme weather on human health, the researchers wrote. Heatwaves are also an issue for mass gatherings and require future planning.

Health experts have questioned whether a fan does more harm than good in heatwaves. One of the review authors, public health expert Dr. Saurabh Gupta of the Hertfordshire Community National Health Service Trust in the UK, said: “It is important to know about the potential benefits and harms of electric fans when choosing whether to use one. This is true if you are simply making a decision about your own use of a fan, but it also applies to broader public health decisions, such as whether to give electric fans to groups of people during a heatwave.”

A fan “might help to increase heat loss if the temperature is below 35 degrees and the fan is not directly aimed at the person,” he wrote, “but when temperatures are above 35 degrees, the fan might actually contribute to heat gain. Excess sweating can also lead to dehydration and other health problems.”

This is particularly important for people who are considered more vulnerable to the effects of heat, such as older adults who are less able to cool down through sweating or increasing the flow of blood to their skin, the team wrote.

The Cochrane researchers discussed how they looked for high quality research that had compared groups of people using fans with groups who didn’t use them during a heatwave. “However, we didn’t find any research that met our requirements. We did find some studies [that] used designs that are less reliable for answering this sort of question, and these had mixed results. Some suggested that fans might reduce health problems, while others suggested that the fans might make things worse.”

Prof. Mike Clarke from the All-Ireland Hub for Trials Methodology Research in Queen’s University Belfast commented in an editorial: “We have shown that the evidence is not already out there on the benefits and harms of electric fans. We need a large randomized trial to resolve this longstanding and ongoing uncertainty and to help people make well-informed choices about their use.”

As a result, the national and local heatwave guidelines that have been published are largely built on evidence from physiological and occupational studies, and there are considerable gaps in the evidence, the Cochrane researchers stated.

They concluded that complete planning is crucial, however, since “if heatwaves become more common, there is an increasing risk of occupational exposure in adults and those exercising in hot weather, including children at school.”

High temperatures can influence mortality, and a range of chronic diseases such as those involving the respiratory, cardiovascular, endocrine and musculoskeletal systems are affected, as are psychiatric patients. Diabetics are known to be at increased risk of dehydration, leading to emergency room admission during hot weather, the researchers wrote, so it is vital to obtain scientific evidence whether fans are enough to relieve the heat.

But the evidence, they concluded, is not there.

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