Medical matters

Drink non-alcoholic fluids and wear loose clothes when the heat is on

Tue, Jul 23, 2013, 01:00

Hasn’t the weather been absolutely amazing? As I write it is another day of dawn to dusk sunshine, with temperatures in the high-20s.

And the week before last I had the somewhat surreal experience of flying into Shannon well after 8pm to be greeted by a temperature of 29 degrees.

The benefits of prolonged sunshine are well known: vitamin D levels rise, mood improves and those prone to pains and aches notice their muscles are more relaxed than usual. On the downside, extremely hot weather can be life-threatening; in Paris in 2003 some 3,000 people dies as a result of two weeks of record-breaking weather.

The health effects of hot weather are linked to the body’s ability to adapt to heat by acting as a natural cooling system. While our adaptation to cold environments is assisted by behavioural responses such as wearing extra layers of clothing, behavioural factors play less of a role in extreme heat.

Scientists have carried out a lot of research into the health risks of extreme weather conditions.When temperature is plotted against the number of daily deaths, a typical U-shaped relationship emerges: the middle trough represents a comfort zone where we are not stressed by heat or cold. The right side of the curve shows the death rate increasing with temperature, with older people most likely to die during extreme heatwaves. Others vulnerable to heatwaves are children and those with mental illnesses. And those with pre-existing illnesses such as heart attack, stroke and chronic breathing problems are also at risk.

The main ways in which the human body eliminates heat during thermal stress are through sweat production, increased cardiac output and redirection of blood flow to the skin. These responses can be diminished or delayed in elderly people or other susceptible groups such as those with chronic illness or people taking certain drugs such as diuretics.

How do we know when someone is overheating dangerously?

The first sign is heat exhaustion which produces symptoms such as excessive thirst, nausea and vomiting and muscle cramps. Remedies for heat exhaustion include removing yourself to a cool room and resting; drinking plenty of fluids but not coffee or alcohol; and changing into loose clothing.

Untreated heat exhaustion progresses to heatstroke. This is defined as a core body temperature of at least 40.6 degrees. Watch out for heavy sweating that suddenly stops; a rapid heart rate and rapid breathing; and neurological symptoms such as confusion and a loss of co-ordination. Heatstroke is a medical emergency: even with prompt medical care some 15 per cent of heatstroke cases are fatal.

There is something of an urban-rural divide when it comes to the health effects of extreme heat. In what is known as the “heat island effect” asphalt and concrete store heat during the day and gradually release it at night, resulting in higher night temperatures. Once the relative humidity rises above 60 per cent or so it interferes with sweat evaporation, thereby depriving the body of a key defence mechanism. And if you live in an urban area you may be prone to develop heat exhaustion during a prolonged heatwave, particularly if there are stagnant atmospheric conditions and poor air.

Infectious disease transmission is also sensitive to climate change. Both the infectious microbes themselves and the vector organisms such as ticks and mosquitoes are affected by alterations in rainfall and temperature. Tick-borne viral encephalitis (inflammation of the brain tissue) has increased in Sweden in response to a succession of warmer winters over the past 20 years. Some reports suggest malaria has increased in the east African highlands in association with local warming because of greater transmission by mosquitoes.

Still, after multi-year summer sunshine droughts we now have this fantastic opportunity to experience a “proper” summer.

So have fun and stay safe.

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