London School of Hygiene & Tropical Medicine

Public bodies need to plan ahead to help people avoid health problems and death during hot weather, and they need to be more aware of how certain drugs are affected by heat, according to a review published online in The Lancet this week. The review, by Dr Shakoor Hajat of the London School of Hygiene and Tropical Medicine and colleagues, discusses how 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.

The hot summers of recent years have led to an alarming increase in the death toll, particularly among the elderly. In 2003, Paris was hit by blistering weather in August and the death toll was almost 15,000 higher than in previous years for the same month.

Over recent years, public bodies have issued advice on ways to cope with hot weather which has included simple measures such as avoiding alcohol, avoiding or reducing physical activity, protecting oneself from the sun and being aware of the symptoms of heat-associated illness. They also suggest looking in on susceptible people such as the elderly, avoiding the hottest part of the day and taking frequent cool baths or showers.

The use of fans, however, is controversial. “Much confusion remains about the use of electric fans during hot weather,” says Shakoor Hajat.”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. Hajat says, “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.”

Previous advice on drug prescribing during hot weather may also be flawed, says Hajat: “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 patients, 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.”

There are certain drugs which can cause problems during heatwaves such as diuretics (often used for heart conditions and high blood pressure) as fluid loss from the body can lead to decreased blood volume, low blood pressure, rapid heart rates and falls. Antipsychotics can affect sweat production.

The authors also suggest that we need to think more deeply about how elderly people can strengthen their physiological defences through acclimatisation. According to Hajat, “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 - for example, 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.”