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The evidence behind the health effects of hot weather


Increasing concerns about climate change and deadly heatwaves in the past mean that the health effects of hot weather are fast becoming a global public health challenge for the 21st century. A Review published Online First looks at the evidence behind advice public bodies give to help people protect themselves against hot weather, and says there needs to be more awareness on how the action of certain drugs are affected by heat. The Review is by Dr Shakoor Hajat, London School of Hygiene and Tropical Medicine, UK, and colleagues.

The most common advice given by public bodies includes: avoid drinking alcohol; wear lightweight, loose fitting clothing; drink regularly without waiting for thirst; if you have no air conditioning at home, seek out an air-conditioned or cool environment ; stay indoors in an air-conditioned environment; wear a hat; avoid or reduce physical activities; protect yourself from the sun; know the symptoms of heat-associated illness and know how to respond; look in on susceptible people; do not leave children in a closed, parked car; avoid going out during the hottest part of the day; and take frequent baths or showers.

The authors say that the evidence behind use of fans to cool down in hot weather is conflicting. They say: "Much confusion remains about the use of electric fans during hot weather. Results of most physiological studies support the use of air currents for cooling, but do not specifically address the issue of household fans. Certainly, there is little to recommend the use of a fan when other, effective, methods are available, such as taking a cool shower."

The authors also question the merits of other commonly given advice, such as avoiding the consumption of alcohol. They say: "This advice is probably overemphasised, and should distinguish between moderate consumption of low-alcohol beverages (when evidence does not strongly support a diuretic effect) and spirits, which should be avoided."

Regarding use of drugs during extreme heat, the authors say: "Drug use is often cited in the plans as a potential risk factor for heat-related illness, but practical advice for appropriate action or adjustment of treatment regimens is rarely provided to readers, other than to check with your doctor. The extent to which health professionals are informed about how to adjust the doses of drugs for a patient during hot weather is unclear."

Examples of drugs that could cause problems in intense heat are diuretics (used to treat heart failure and high blood pressure among other conditions), since water loss from the body can lead to decreased blood volume, low blood pressure, and to rapid heart rate and falls. Care should also be taken with antipsychotic drugs since these affect sweat production.

The authors say that studies are needed on how elderly people can strengthen their physiological defences through acclimatisation. They say: "A potentially valuable issue that has been given little attention is the notion of gradual acclimatisation to heat in elderly people to build up their physiological defences. Although advice to stay in an air-conditioned environment is well supported by evidence, avoidance of outdoor temperatures and strenuous exercise might deprive elderly individuals of the opportunity to train their sweat glands. So far, little is known about the extent to which people in their 70s and 80s, and those with chronic medical conditions, can attain such acclimatisation. Advice about activity should draw on experimental evidence available from sports, military, and occupational settings, in which techniques to make activity during hot weather safe have been identified-- eg, precooling the body before activity."

The authors conclude: "With rises in temperatures expected in the coming decades, use of evidence-based health protection during hot weather by the general public and public health practitioners will have a key role in determining future heat burdens."


Dr Shakoor Hajat, London School of Hygiene and Tropical Medicine, UK. T) +44 (0) 20 7612 7844 E)

For full Review, see:

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