Electric fans for reducing the health effects of heatwaves

Heatwaves are set to become more common and their effects can be devastating. For example, up to 30,000 people may have died because of the heatwave that occurred in Europe during August 2003. One way to try to get relief from the heat is to use an electric fan, but whether this will do more good or harm is uncertain. A fan might help to increase heat loss if the temperature is below 35 °C and the fan is not directly aimed at the person, but, when temperatures are above 35 °C, the fan might actually contribute to heat gain. Excess sweating can also lead to dehydration and other health problems. It is important, therefore, to know about the potential benefits and harms of electric fans when choosing whether to use one. This applies if the decision is about your own use of a fan, but it is also relevant to broader public health decisions, such as whether to give electric fans to groups of people during a heatwave. 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.

This Cochrane Review tried to provide some of the answers that would help decision makers. We 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 which 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.

Therefore, the research that has been done to date does not resolve uncertainties about the health effects of electric fans during heatwaves. People who have to make decisions should consider the current evidence, alongside local policies and guidelines when making their choices. They may wish to help resolve the continuing uncertainty by conducting the type of high quality research that would provide the reliable evidence needed to determine the benefits and harms of using electric fans during a heatwave.

Authors' conclusions: 

The evidence we identified does not resolve uncertainties about the health effects of electric fans during heatwaves. Therefore, this review does not support or refute the use of electric fans during a heatwave. People making decisions about electric fans should consider the current state of the evidence base, and they might also wish to make themselves aware of local policy or guidelines when making a choice about whether or not to use or supply electric fans. The main implication of this review is that high quality research is needed to resolve the long standing and ongoing uncertainty about the benefits and harms of using electric fans during a heatwave, for example randomised trials comparing the health effects in people with electric fans to those in people without them.

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Background: 

Heatwaves are hot weather events, which breach regional or national thresholds, that last for several days. They are likely to occur with increasing frequency in some parts of the world. The potential consequences were illustrated in Europe in August 2003 when there were an estimated 30,000 excess deaths due to a heatwave. Electric fans might be used with the intention of reducing the adverse health effects of a heatwave. Fans do not cool the ambient air but can be used to draw in cooler air from outside when placed at an open window. The aim of the fans would be to increase heat loss by increasing the efficiency of all normal methods of heat loss, but particularly by evaporation and convection methods. However, it should be noted that increased sweating can lead to dehydration and electrolyte imbalances if these fluids and electrolytes are not replaced quickly enough. Research has also identified important gaps in knowledge about the use of fans, which might lead to their inappropriate use.

Objectives: 

To determine whether the use of electric fans contributes to, or impedes, heat loss at high ambient temperatures during a heatwave, and to contribute to the evidence base for the public health impacts of heatwaves.

Search strategy: 

We sought unpublished and published studies that had been published in any language. The review team were able to assess studies reported in English, Chinese, Dutch, French and German; and reports in other languages would have been translated into English as necessary. We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL, the Indian biomedical literature (IndMED and MedIND) and databases of Chinese literature (Chinese Journal Net and Digital Periodical of WanFang Data). The most recent electronic searches were done in April 2012. We also checked the reference lists of relevant articles and the websites of relevant national and international organisations, and consulted with researchers and policy makers with experience in strategies to manage heatwaves to identify additional studies. The titles and abstracts from each search were checked independently by two review authors. The full text articles that we retrieved were checked independently by at least two authors for their relevance and for references to potentially eligible studies.

Selection criteria: 

Randomised trials and other experimental designs, such as interrupted time series and controlled before-and-after studies, comparing the use of electric fans with no fans during a heatwave were eligible for this review. The electric fans could be hand-held (battery operated), portable or mounted on the wall or ceiling, or in a window. We sought interventions delivered to anyone for whom a heatwave was likely to have serious adverse health impacts. This would include people of all ages but with a particular focus on some groups (for example older people). Populations from high-, middle- and low-income countries were eligible for the review.

Data collection and analysis: 

If we had identified eligible studies, they would have been assessed independently by at least two review authors and data would have been extracted on the characteristics of the study, its participants and interventions, as well as the effects on health outcomes. The primary outcomes were mortality, hospital admission and other contacts with healthcare services.

Main results: 

We did not identify any eligible studies despite the extensive searching and correspondence with several experts in this topic area. We identified retrospective, observational studies, usually with a case-control design, that investigated the association between the use of electric fans and health outcomes, including death. The results of these studies were mixed. Some studies found that the use of fans was associated with better health outcomes, others found the reverse.

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