Use of physiological evidence for heatwave public policy
Authors: Ollie Jay, Anthony Capon
Journal: The Lancet Planetary Health (2018)

Very high temperatures across Europe last summer served as a reminder of the harmful health effects of heatwaves, which are expected to increase in frequency, intensity, and duration in the future because of climate change.1Watts N Adger WN Agnolucci P et al.Health and climate change: policy responses to protect public health.Lancet. 2015; 386: 1861-1914Summary Full Text Full Text PDF PubMed Scopus (1017) Google Scholar A coherent public health plan for hot weather and heatwaves is essential to protect the health of everyone. Yet, there is a pressing need to ensure that a key component of such plans—the recommendation of personal cooling strategies that mitigates physiological heat strain—is informed by valid scientific evidence. The most commonly recommended cooling strategy is the use of air conditioning,2Hajat S O'Connor M Kosatsky T Health effects of hot weather: from awareness of risk factors to effective health protection.Lancet. 2010; 375: 856-863Summary Full Text Full Text PDF PubMed Scopus (286) Google Scholar which provides the greatest protection against heat-related illnesses; however, it is not affordable for many of the most vulnerable people. Moreover, widespread use of air conditioning in heavily populated regions often sees demand for electricity threatened by the capacity to supply, leading to a greater likelihood of power outages. Additionally, the enormous environmental impact of the projected escalation in future air conditioning use on a global scale has been well described.3Davis LW Gertler PJ Contribution of air conditioning adoption to future energy use under global warming.Proc Natl Acad Sci USA. 2015; 112: 5962-5967Crossref PubMed Scopus (308) Google Scholar Electric fans offer an alternative cooling strategy, with up to 50 times lower electricity requirement and economic cost than air conditioning. Despite no supporting experimental evidence, many public health authorities, including WHO, continue to state that fans should not be used when ambient temperatures exceed 35°C because they accelerate heat exhaustion and exacerbate dehydration. Recently, thermal physiologists have shown that electric fans ameliorate heat-related increases in physiological strain in healthy young men at air temperatures of at least 42°C and 50% relative humidity, with additional sweat losses that can be replaced by drinking extra water (200 mL/h).4Ravanelli NM Hodder SG Havenith G Jay O Heart rate and body temperature responses to extreme heat and humidity with and without electric fans.JAMA. 2015; 313: 724-725Crossref PubMed Scopus (53) Google Scholar Because of age-related decrements in sweating, fans are not beneficial for healthy people aged 65 years or older in the same environmental conditions, and indeed might be harmful.5Gagnon D Romero SA Cramer MN Jay O Crandall CG Cardiac and thermal strain of elderly adults exposed to extreme heat and humidity with and without electric fan use.JAMA. 2016; 316: 989-991Crossref PubMed Scopus (19) Google Scholar However, fans could theoretically still be effective in this subgroup if water is externally applied to the skin to assist evaporation. This notion remains to be experimentally verified. Identification of effective and sustainable ways of cooling is essential. Physiologists can provide valuable evidence by systematically assessing the efficacy of various strategies for mitigating heat-related strain of different subgroups, including clinical groups, in climate-controlled chambers that simulate historical and future heatwaves. However, collaboration with public health authorities, and the wider medical community, is needed to ensure that experimental findings are translated into evidence-based public health advice. We declare no competing interests.